（4.2.7.3）Android PullToRefresh 分析之三、手势响应

转载请标明出处：

http://blog.csdn.net/xuehuayous/article/details/50352196

本文出自:【Kevin.zhou的博客】

前言：接着上一篇《Android PullToRefresh
分析之二、UI结构》，这一篇主要分析是如何响应手势事件的，即我们手指滑动的时候促发的一系列响应，该篇将详细讲清楚。

一、 问题思考

我们首先来思考下如果让我们做手势响应要考虑哪些问题， 我们先提出几个问题：

向下滑动时如何判断滑动到了头部？
滑动到头部之后是马上就促发刷新操作吗？

OK，来分析下这两个问题：

（1）判断滑动到了头部，如下两图所示：向下滑动但是第一个条目还没有完全显示，这个时候是不能促发刷新操作的；



（2）只有第一个条目完全可见才能促发刷新动作的开始，如下图所示，第一个条目完全可见；



（3）只有第一个条目完全显示后再往下滑动，开始促发刷新动作的开始，这里为什么说刷新动作的开始呢？因为刷新动作又可以分解为三个阶段四种状态，①、"刷新头部"开始显示 ②、"刷新头部"完全显示
③、"刷新头部"完全显示后释放 ④、"刷新头部"未完全显示就释放



（4）当"刷新头部"完全显示的时候，放开就会调用回调方法onPullDownToRefresh()，让我们去更新数据

二、源码分析

通过以上问题的了解，我们再分析源码就好理解了，下面来对源码进行分析。
在PullToRefreshBase中关于手势识别的代码就在两个方法的回调中，onInterceptTouchEvent()和onTouchEvent()，如果这两个方法的作用就不再详细说明，onInterceptTouchEvent()作用就是判断是否把该事件分发给子View，具体的说明请参考《Android-onInterceptTouchEvent()和onTouchEvent()总结》，这篇文章讲述的比较清楚。

首先来看下onInterceptTouchEvent()方法：

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@Override

public final boolean onInterceptTouchEvent(MotionEvent event) {

// 1、如果不是刷新加载模式，让子View接收触摸事件

if (!isPullToRefreshEnabled()) {

return false;

}

final int action = event.getAction();

// 2、如果当前手势被释放或手指抬起，让子View接收触摸事件

if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) {

mIsBeingDragged = false;

return false;

}

// 3、如果手指按下，并且已经处在滑动刷新加载状态，不让子View接收触摸事件

if (action != MotionEvent.ACTION_DOWN && mIsBeingDragged) {

return true;

}

switch (action) {

case MotionEvent.ACTION_MOVE: {

// If we're refreshing, and the flag is set. Eat all MOVE events

// 4、如果在刷新加载时不允许再次滑动而且正在刷新状态，不让子View接收触摸事件

// 即正在加载数据时不允许用户再次滑动刷新，只能等待该次数据加载完成

if (!mScrollingWhileRefreshingEnabled && isRefreshing()) {

return true;

}

if (isReadyForPull()) {

final float y = event.getY(), x = event.getX();

final float diff, oppositeDiff, absDiff;

// We need to use the correct values, based on scroll

// direction

switch (getPullToRefreshScrollDirection()) {

case HORIZONTAL:

diff = x - mLastMotionX;

oppositeDiff = y - mLastMotionY;

break;

case VERTICAL:

default:

diff = y - mLastMotionY;

oppositeDiff = x - mLastMotionX;

break;

}

absDiff = Math.abs(diff);

// 滑动距离大于滑动事件触发的最小距离，刷新方向上滑动的距离大于非刷新方向的距离

if (absDiff > mTouchSlop && (!mFilterTouchEvents || absDiff > Math.abs(oppositeDiff))) {

// 第一个条目完全可见且为向下滑动，设置当前为 头部刷新

if (mMode.showHeaderLoadingLayout() && diff >= 1f && isReadyForPullStart()) {

mLastMotionY = y;

mLastMotionX = x;

// 5、触发头部刷新，不让子View接收触摸事件

mIsBeingDragged = true;

if (mMode == Mode.BOTH) {

mCurrentMode = Mode.PULL_FROM_START;

}

// 最后一个条目完全可见且为向上滑动，设置当前为 尾部加载

} else if (mMode.showFooterLoadingLayout() && diff <= -1f && isReadyForPullEnd()) {

mLastMotionY = y;

mLastMotionX = x;

// 6、触发尾部加载，不让子View接收触摸事件

mIsBeingDragged = true;

if (mMode == Mode.BOTH) {

mCurrentMode = Mode.PULL_FROM_END;

}

}

}

}

break;

}

case MotionEvent.ACTION_DOWN: {

if (isReadyForPull()) {

mLastMotionY = mInitialMotionY = event.getY();

mLastMotionX = mInitialMotionX = event.getX();

mIsBeingDragged = false;

}

break;

}

}

return mIsBeingDragged;

}

通过以上代码的注释也可以看出，onInterceptTouchEvent()主要处理的就是在刷新加载的时候不允许子View获取该触摸事件，其实我们最关心的是是否开始刷新加载mIsBeingDragged的状态切换！！！
值得一提的是判断第一个条目是否完全显示、最后一个条目是否完全显示是通过抽象的方法isReadyForPullStart()、isReadyForPullEnd()由子类实现的。

然后分析onTouchEvent()方法：

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@Override

public final boolean onTouchEvent(MotionEvent event) {

......

switch (event.getAction()) {

case MotionEvent.ACTION_MOVE: {

if (mIsBeingDragged) {

mLastMotionY = event.getY();

mLastMotionX = event.getX();

pullEvent();

return true;

}

break;

}

......

case MotionEvent.ACTION_CANCEL:

case MotionEvent.ACTION_UP: {

if (mIsBeingDragged) {

mIsBeingDragged = false;

if (mState == State.RELEASE_TO_REFRESH

&& (null != mOnRefreshListener || null != mOnRefreshListener2)) {

setState(State.REFRESHING, true);

return true;

}

// If we're already refreshing, just scroll back to the top

if (isRefreshing()) {

smoothScrollTo(0);

return true;

}

// If we haven't returned by here, then we're not in a state

// to pull, so just reset

setState(State.RESET);

return true;

}

break;

}

}

return false;

}

其实该方法中主要的就是ACTION_MOVE中调用的pullEvent()（注意的是只有在mIsBeingDragged == ture状态才会执行pullEvent()，就是为什么我在onInterceptTouchEvent()分析时说"我们最关心的是是否开始刷新加载mIsBeingDragged的状态切换！！！"）， 及MotionEvent.ACTION_UP中调用的setState()，接着看pullEvent()方法：

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private void pullEvent() {

final int newScrollValue;

final int itemDimension;

final float initialMotionValue, lastMotionValue;

switch (getPullToRefreshScrollDirection()) {

case HORIZONTAL:

initialMotionValue = mInitialMotionX;

lastMotionValue = mLastMotionX;

break;

case VERTICAL:

default:

initialMotionValue = mInitialMotionY;

lastMotionValue = mLastMotionY;

break;

}

switch (mCurrentMode) {

case PULL_FROM_END:

newScrollValue = Math.round(Math.max(initialMotionValue - lastMotionValue, 0) / FRICTION);

itemDimension = getFooterSize();

break;

case PULL_FROM_START:

default:

newScrollValue = Math.round(Math.min(initialMotionValue - lastMotionValue, 0) / FRICTION);

itemDimension = getHeaderSize();

break;

}

setHeaderScroll(newScrollValue);

if (newScrollValue != 0 && !isRefreshing()) {

float scale = Math.abs(newScrollValue) / (float) itemDimension;

......

if (mState != State.PULL_TO_REFRESH && itemDimension >= Math.abs(newScrollValue)) {

setState(State.PULL_TO_REFRESH);

} else if (mState == State.PULL_TO_REFRESH && itemDimension < Math.abs(newScrollValue)) {

setState(State.RELEASE_TO_REFRESH);

}

}

}

可以看到主要是根据刷新状态获取头部或者尾部的大小，然后调用了setHeaderScroll()方法，进入该方法：

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protected final void setHeaderScroll(int value) {

......

if (mLayoutVisibilityChangesEnabled) {

if (value < 0) {

mHeaderLayout.setVisibility(View.VISIBLE);

} else if (value > 0) {

mFooterLayout.setVisibility(View.VISIBLE);

} else {

mHeaderLayout.setVisibility(View.INVISIBLE);

mFooterLayout.setVisibility(View.INVISIBLE);

}

}

......

switch (getPullToRefreshScrollDirection()) {

case VERTICAL:

scrollTo(0, value);

break;

case HORIZONTAL:

scrollTo(value, 0);

break;

}

}

可以看到也比较简单，就是根据向下还是向上滑动来设置头部或尾部的显示，然后控件随手指滚动，这样头部或者尾部就显示出来了。然后回到pullEvent()方法，有如下代码比较关键：

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if (mState != State.PULL_TO_REFRESH && itemDimension >= Math.abs(newScrollValue)) {

setState(State.PULL_TO_REFRESH);

} else if (mState == State.PULL_TO_REFRESH && itemDimension < Math.abs(newScrollValue)) {

setState(State.RELEASE_TO_REFRESH);

}

当滑动距离大于头部或尾部大小的时候，设置状态为释放以刷新，这就是我们上面所说的刷新头部或尾部完全显示，这时候放开手指就可以触发刷新加载的回调。接着回到onTouchEvent()方法的手指抬起，有如下关键代码：

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if (mState == State.RELEASE_TO_REFRESH

&& (null != mOnRefreshListener || null != mOnRefreshListener2)) {

setState(State.REFRESHING, true);

return true;

}

就是释放的时候回调刷新加载的方法，我们就可以通过设置监听的方式在回调方法中来处理刷新加载的事件啦~

三、结语

在该篇中，我们也是搞清楚了一个问题，就是如何响应手指滑动事件的。在下篇中《Android
PullToRefresh 分析之四、扩展RecyclerView》我们主要讲解如何判断刷新加载View是如何判断是否第一个条目完全显示，最后一个条目完全显示的，然后编写一个自己的扩展 PullToRefreshRecyclerView。

/*******************************************************************************
* Copyright 2011, 2012 Chris Banes.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0 *
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*******************************************************************************/
package com.handmark.pulltorefresh.library;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.drawable.Drawable;
import android.os.Build.VERSION;
import android.os.Build.VERSION_CODES;
import android.os.Bundle;
import android.os.Parcelable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.animation.DecelerateInterpolator;
import android.view.animation.Interpolator;
import android.widget.FrameLayout;
import android.widget.LinearLayout;

import com.handmark.pulltorefresh.library.internal.FlipLoadingLayout;
import com.handmark.pulltorefresh.library.internal.LoadingLayout;
import com.handmark.pulltorefresh.library.internal.RotateLoadingLayout;
import com.handmark.pulltorefresh.library.internal.Utils;
import com.handmark.pulltorefresh.library.internal.ViewCompat;

public abstract class PullToRefreshBase<T extends View> extends LinearLayout implements IPullToRefresh<T> {

// ===========================================================
// Constants
// ===========================================================

static final boolean DEBUG = true;

static final boolean USE_HW_LAYERS = false;

static final String LOG_TAG = "PullToRefresh";

static final float FRICTION = 2.0f;

public static final int SMOOTH_SCROLL_DURATION_MS = 200;
public static final int SMOOTH_SCROLL_LONG_DURATION_MS = 325;
static final int DEMO_SCROLL_INTERVAL = 225;

static final String STATE_STATE = "ptr_state";
static final String STATE_MODE = "ptr_mode";
static final String STATE_CURRENT_MODE = "ptr_current_mode";
static final String STATE_SCROLLING_REFRESHING_ENABLED = "ptr_disable_scrolling";
static final String STATE_SHOW_REFRESHING_VIEW = "ptr_show_refreshing_view";
static final String STATE_SUPER = "ptr_super";

// ===========================================================
// Fields
// ===========================================================

private int mTouchSlop;//滑动事件触发的最小距离
private float mLastMotionX, mLastMotionY;
private float mInitialMotionX, mInitialMotionY;

private boolean mIsBeingDragged = false;  // 是否处于 刷新 加载中（包括 拽拉 和 释放动作）
private State mState = State.RESET;
private Mode mMode = Mode.getDefault();

private Mode mCurrentMode; //当前动作  出发了的  加载 or 刷新
T mRefreshableView;
private FrameLayout mRefreshableViewWrapper;

private boolean mShowViewWhileRefreshing = true;
private boolean mScrollingWhileRefreshingEnabled = false; //配置  刷新加载时是否允许再次滑动
private boolean mFilterTouchEvents = true;
private boolean mOverScrollEnabled = true;
private boolean mLayoutVisibilityChangesEnabled = true;

private Interpolator mScrollAnimationInterpolator;
private AnimationStyle mLoadingAnimationStyle = AnimationStyle.getDefault();

private LoadingLayout mHeaderLayout;
private LoadingLayout mFooterLayout;

private OnRefreshListener<T> mOnRefreshListener;
private OnRefreshListener2<T> mOnRefreshListener2;
private OnPullEventListener<T> mOnPullEventListener;

private SmoothScrollRunnable mCurrentSmoothScrollRunnable;

// ===========================================================
// Constructors
// ===========================================================

public PullToRefreshBase(Context context) {
super(context);
init(context, null);
}

public PullToRefreshBase(Context context, AttributeSet attrs) {
super(context, attrs);
init(context, attrs);
}

public PullToRefreshBase(Context context, Mode mode) {
super(context);
mMode = mode;
init(context, null);
}

public PullToRefreshBase(Context context, Mode mode, AnimationStyle animStyle) {
super(context);
mMode = mode;
mLoadingAnimationStyle = animStyle;
init(context, null);
}

@Override
public void addView(View child, int index, ViewGroup.LayoutParams params) {
if (DEBUG) {
Log.d(LOG_TAG, "addView: " + child.getClass().getSimpleName());
}

final T refreshableView = getRefreshableView();

if (refreshableView instanceof ViewGroup) {
((ViewGroup) refreshableView).addView(child, index, params);
} else {
throw new UnsupportedOperationException("Refreshable View is not a ViewGroup so can't addView");
}
}

@Override
public final boolean demo() {
if (mMode.showHeaderLoadingLayout() && isReadyForPullStart()) {
smoothScrollToAndBack(-getHeaderSize() * 2);
return true;
} else if (mMode.showFooterLoadingLayout() && isReadyForPullEnd()) {
smoothScrollToAndBack(getFooterSize() * 2);
return true;
}

return false;
}

@Override
public final Mode getCurrentMode() {
return mCurrentMode;
}

@Override
public final boolean getFilterTouchEvents() {
return mFilterTouchEvents;
}

@Override
public final ILoadingLayout getLoadingLayoutProxy() {
return getLoadingLayoutProxy(true, true);
}

@Override
public final ILoadingLayout getLoadingLayoutProxy(boolean includeStart, boolean includeEnd) {
return createLoadingLayoutProxy(includeStart, includeEnd);
}

@Override
public final Mode getMode() {
return mMode;
}

@Override
public final T getRefreshableView() {
return mRefreshableView;
}

@Override
public final boolean getShowViewWhileRefreshing() {
return mShowViewWhileRefreshing;
}

@Override
public final State getState() {
return mState;
}

/**
* @deprecated See {@link #isScrollingWhileRefreshingEnabled()}.
*/
public final boolean isDisableScrollingWhileRefreshing() {
return !isScrollingWhileRefreshingEnabled();
}

@Override
public final boolean isPullToRefreshEnabled() {
return mMode.permitsPullToRefresh();
}

@Override
public final boolean isPullToRefreshOverScrollEnabled() {
return VERSION.SDK_INT >= VERSION_CODES.GINGERBREAD && mOverScrollEnabled
&& OverscrollHelper.isAndroidOverScrollEnabled(mRefreshableView);
}

@Override
public final boolean isRefreshing() {
return mState == State.REFRESHING || mState == State.MANUAL_REFRESHING;
}

@Override
public final boolean isScrollingWhileRefreshingEnabled() {
return mScrollingWhileRefreshingEnabled;
}

//是否拦截该touch事件
//onInterceptTouchEvent()主要处理的就是在刷新加载的时候不允许子View获取该触摸事件，其实我们最关心的是是否开始刷新加载mIsBeingDragged的状态切换！！！
//值得一提的是判断第一个条目是否完全显示、最后一个条目是否完全显示是通过抽象的方法isReadyForPullStart()、isReadyForPullEnd()由子类实现的
@Override
public final boolean onInterceptTouchEvent(MotionEvent event) {

// 1、如果不是刷新加载模式，让子View接收触摸事件
if (!isPullToRefreshEnabled()) {
return false;
}

final int action = event.getAction();

// 2、如果当前手势被释放或手指抬起，让子View接收触摸事件
if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) {
mIsBeingDragged = false;
return false;
}

// 3、如果手指松开，并且已经处在滑动刷新加载状态，不让子View接收触摸事件
if (action != MotionEvent.ACTION_DOWN && mIsBeingDragged) {
return true;
}

switch (action) {
case MotionEvent.ACTION_MOVE: {
// If we're refreshing, and the flag is set. Eat all MOVE events
// 4、如果在刷新加载时不允许再次滑动而且正在刷新状态，不让子View接收触摸事件
// 即正在加载数据时不允许用户再次滑动刷新，只能等待该次数据加载完成
if (!mScrollingWhileRefreshingEnabled && isRefreshing()) {
return true;
}

// 如果已经到达该滚动的临界值了，由具体子view实现控制
if (isReadyForPull()) {
final float y = event.getY(), x = event.getX(); //当前移动到的点的距离
final float diff, oppositeDiff, absDiff; //与上次点的间距：期望轴，不期望轴，期望轴的绝对值

// We need to use the correct values, based on scroll
// direction
switch (getPullToRefreshScrollDirection()) {
case HORIZONTAL:
diff = x - mLastMotionX; //如果是水平，则计算水平间距==期望轴
oppositeDiff = y - mLastMotionY;
break;
case VERTICAL:
default:
diff = y - mLastMotionY;//如果是水平，则计算垂直间距==期望轴
oppositeDiff = x - mLastMotionX;
break;
}
absDiff = Math.abs(diff);//间距绝对值

// 滑动距离大于滑动事件触发的最小距离，刷新方向上滑动的距离大于非刷新方向的距离
if (absDiff > mTouchSlop && (!mFilterTouchEvents || absDiff > Math.abs(oppositeDiff))) {
// 第一个条目完全可见且为向下滑动，设置当前为 头部刷新
if (mMode.showHeaderLoadingLayout() && diff >= 1f && isReadyForPullStart()) {
mLastMotionY = y;
mLastMotionX = x;
// 5、触发头部刷新，不让子View接收触摸事件
mIsBeingDragged = true;
if (mMode == Mode.BOTH) {
mCurrentMode = Mode.PULL_FROM_START;
}
// 最后一个条目完全可见且为向上滑动，设置当前为 尾部加载
} else if (mMode.showFooterLoadingLayout() && diff <= -1f && isReadyForPullEnd()) {
mLastMotionY = y;
mLastMotionX = x;
// 6、触发尾部加载，不让子View接收触摸事件
mIsBeingDragged = true;
if (mMode == Mode.BOTH) {
mCurrentMode = Mode.PULL_FROM_END;
}
}
}
}
break;
}
case MotionEvent.ACTION_DOWN: {
if (isReadyForPull()) {
mLastMotionY = mInitialMotionY = event.getY();
mLastMotionX = mInitialMotionX = event.getX();
mIsBeingDragged = false;
}
break;
}
}

return mIsBeingDragged;
}

@Override
public final void onRefreshComplete() {
if (isRefreshing()) {
setState(State.RESET);
}
}

@Override
public final boolean onTouchEvent(MotionEvent event) {

// 1、如果不是刷新加载模式，让子View接收触摸事件
if (!isPullToRefreshEnabled()) {
return false;
}

// If we're refreshing, and the flag is set. Eat the event
if (!mScrollingWhileRefreshingEnabled && isRefreshing()) {
return true;
}

if (event.getAction() == MotionEvent.ACTION_DOWN && event.getEdgeFlags() != 0) {
return false;
}

switch (event.getAction()) {
case MotionEvent.ACTION_MOVE: {
//注意的是只有在mIsBeingDragged == ture状态才会执行pullEvent()
// 就是为什么我在onInterceptTouchEvent()分析时说"我们最关心的是是否开始刷新加载mIsBeingDragged的状态切换！！！"
if (mIsBeingDragged) {
mLastMotionY = event.getY();
mLastMotionX = event.getX();
pullEvent();
return true;
}
break;
}

case MotionEvent.ACTION_DOWN: {
//// 如果已经到达该滚动的临界值了，由具体子view实现控制
//开始拦截，并记录初始值
if (isReadyForPull()) {
mLastMotionY = mInitialMotionY = event.getY();
mLastMotionX = mInitialMotionX = event.getX();
return true;
}
break;
}

case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP: {
if (mIsBeingDragged) {
mIsBeingDragged = false;

//释放的时候回调刷新加载的方法，我们就可以通过设置监听的方式在回调方法中来处理刷新加载的事件
if (mState == State.RELEASE_TO_REFRESH
&& (null != mOnRefreshListener || null != mOnRefreshListener2)) {
setState(State.REFRESHING, true);
return true;
}

// If we're already refreshing, just scroll back to the top
if (isRefreshing()) {
smoothScrollTo(0);
return true;
}

// If we haven't returned by here, then we're not in a state
// to pull, so just reset
setState(State.RESET);

return true;
}
break;
}
}

return false;
}

public final void setScrollingWhileRefreshingEnabled(boolean allowScrollingWhileRefreshing) {
mScrollingWhileRefreshingEnabled = allowScrollingWhileRefreshing;
}

/**
* @deprecated See {@link #setScrollingWhileRefreshingEnabled(boolean)}
*/
public void setDisableScrollingWhileRefreshing(boolean disableScrollingWhileRefreshing) {
setScrollingWhileRefreshingEnabled(!disableScrollingWhileRefreshing);
}

@Override
public final void setFilterTouchEvents(boolean filterEvents) {
mFilterTouchEvents = filterEvents;
}

/**
* @deprecated You should now call this method on the result of
*             {@link #getLoadingLayoutProxy()}.
*/
public void setLastUpdatedLabel(CharSequence label) {
getLoadingLayoutProxy().setLastUpdatedLabel(label);
}

/**
* @deprecated You should now call this method on the result of
*             {@link #getLoadingLayoutProxy()}.
*/
public void setLoadingDrawable(Drawable drawable) {
getLoadingLayoutProxy().setLoadingDrawable(drawable);
}

/**
* @deprecated You should now call this method on the result of
*             {@link #getLoadingLayoutProxy(boolean, boolean)}.
*/
public void setLoadingDrawable(Drawable drawable, Mode mode) {
getLoadingLayoutProxy(mode.showHeaderLoadingLayout(), mode.showFooterLoadingLayout()).setLoadingDrawable(
drawable);
}

@Override
public void setLongClickable(boolean longClickable) {
getRefreshableView().setLongClickable(longClickable);
}

@Override
public final void setMode(Mode mode) {
if (mode != mMode) {
if (DEBUG) {
Log.d(LOG_TAG, "Setting mode to: " + mode);
}
mMode = mode;
updateUIForMode();
}
}

public void setOnPullEventListener(OnPullEventListener<T> listener) {
mOnPullEventListener = listener;
}

@Override
public final void setOnRefreshListener(OnRefreshListener<T> listener) {
mOnRefreshListener = listener;
mOnRefreshListener2 = null;
}

@Override
public final void setOnRefreshListener(OnRefreshListener2<T> listener) {
mOnRefreshListener2 = listener;
mOnRefreshListener = null;
}

/**
* @deprecated You should now call this method on the result of
*             {@link #getLoadingLayoutProxy()}.
*/
public void setPullLabel(CharSequence pullLabel) {
getLoadingLayoutProxy().setPullLabel(pullLabel);
}

/**
* @deprecated You should now call this method on the result of
*             {@link #getLoadingLayoutProxy(boolean, boolean)}.
*/
public void setPullLabel(CharSequence pullLabel, Mode mode) {
getLoadingLayoutProxy(mode.showHeaderLoadingLayout(), mode.showFooterLoadingLayout()).setPullLabel(pullLabel);
}

/**
* @param enable Whether Pull-To-Refresh should be used
* @deprecated This simple calls setMode with an appropriate mode based on
*             the passed value.
*/
public final void setPullToRefreshEnabled(boolean enable) {
setMode(enable ? Mode.getDefault() : Mode.DISABLED);
}

@Override
public final void setPullToRefreshOverScrollEnabled(boolean enabled) {
mOverScrollEnabled = enabled;
}

@Override
public final void setRefreshing() {
setRefreshing(true);
}

@Override
public final void setRefreshing(boolean doScroll) {
if (!isRefreshing()) {
setState(State.MANUAL_REFRESHING, doScroll);
}
}

/**
* @deprecated You should now call this method on the result of
*             {@link #getLoadingLayoutProxy()}.
*/
public void setRefreshingLabel(CharSequence refreshingLabel) {
getLoadingLayoutProxy().setRefreshingLabel(refreshingLabel);
}

/**
* @deprecated You should now call this method on the result of
*             {@link #getLoadingLayoutProxy(boolean, boolean)}.
*/
public void setRefreshingLabel(CharSequence refreshingLabel, Mode mode) {
getLoadingLayoutProxy(mode.showHeaderLoadingLayout(), mode.showFooterLoadingLayout()).setRefreshingLabel(
refreshingLabel);
}

/**
* @deprecated You should now call this method on the result of
*             {@link #getLoadingLayoutProxy()}.
*/
public void setReleaseLabel(CharSequence releaseLabel) {
setReleaseLabel(releaseLabel, Mode.BOTH);
}

/**
* @deprecated You should now call this method on the result of
*             {@link #getLoadingLayoutProxy(boolean, boolean)}.
*/
public void setReleaseLabel(CharSequence releaseLabel, Mode mode) {
getLoadingLayoutProxy(mode.showHeaderLoadingLayout(), mode.showFooterLoadingLayout()).setReleaseLabel(
releaseLabel);
}

public void setScrollAnimationInterpolator(Interpolator interpolator) {
mScrollAnimationInterpolator = interpolator;
}

@Override
public final void setShowViewWhileRefreshing(boolean showView) {
mShowViewWhileRefreshing = showView;
}

/**
* 获取刷新加载的方向，是横向还是竖向
* @return Either {@link Orientation#VERTICAL} or
*         {@link Orientation#HORIZONTAL} depending on the scroll direction.
*/
public abstract Orientation getPullToRefreshScrollDirection();

final void setState(State state, final boolean... params) {
mState = state;
if (DEBUG) {
Log.d(LOG_TAG, "State: " + mState.name());
}

switch (mState) {
case RESET:
onReset();
break;
case PULL_TO_REFRESH:
onPullToRefresh();
break;
case RELEASE_TO_REFRESH:
onReleaseToRefresh();
break;
case REFRESHING:
case MANUAL_REFRESHING:
onRefreshing(params[0]);
break;
case OVERSCROLLING:
// NO-OP
break;
}

// Call OnPullEventListener
if (null != mOnPullEventListener) {
mOnPullEventListener.onPullEvent(this, mState, mCurrentMode);
}
}

/**
* Used internally for adding view. Need because we override addView to
* pass-through to the Refreshable View
*/
protected final void addViewInternal(View child, int index, ViewGroup.LayoutParams params) {
super.addView(child, index, params);
}

/**
* Used internally for adding view. Need because we override addView to
* pass-through to the Refreshable View
*/
protected final void addViewInternal(View child, ViewGroup.LayoutParams params) {
super.addView(child, -1, params);
}

//在初始化头部和尾部的时候都是调用的createLoadingLayout()方法，只是传入的参数不同
//调用的LoadingAnimationStyle类的createLoadingLayout()方法
protected LoadingLayout createLoadingLayout(Context context, Mode mode, TypedArray attrs) {
LoadingLayout layout = mLoadingAnimationStyle.createLoadingLayout(context, mode,
getPullToRefreshScrollDirection(), attrs);
layout.setVisibility(View.INVISIBLE);
return layout;
}

/**
* Used internally for {@link #getLoadingLayoutProxy(boolean, boolean)}.
* Allows derivative classes to include any extra LoadingLayouts.
*/
protected LoadingLayoutProxy createLoadingLayoutProxy(final boolean includeStart, final boolean includeEnd) {
LoadingLayoutProxy proxy = new LoadingLayoutProxy();

if (includeStart && mMode.showHeaderLoadingLayout()) {
proxy.addLayout(mHeaderLayout);
}
if (includeEnd && mMode.showFooterLoadingLayout()) {
proxy.addLayout(mFooterLayout);
}

return proxy;
}

/**
* 生成刷新加载View，这里生成的是ScrollView
* This is implemented by derived classes to return the created View. If you
* need to use a custom View (such as a custom ListView), override this
* method and return an instance of your custom class.
* <p/>
* Be sure to set the ID of the view in this method, especially if you're
* using a ListActivity or ListFragment.
*
* @param context Context to create view with
* @param attrs AttributeSet from wrapped class. Means that anything you
*            include in the XML layout declaration will be routed to the
*            created View
* @return New instance of the Refreshable View
*/
protected abstract T createRefreshableView(Context context, AttributeSet attrs);

protected final void disableLoadingLayoutVisibilityChanges() {
mLayoutVisibilityChangesEnabled = false;
}

protected final LoadingLayout getFooterLayout() {
return mFooterLayout;
}

protected final int getFooterSize() {
return mFooterLayout.getContentSize();
}

protected final LoadingLayout getHeaderLayout() {
return mHeaderLayout;
}

protected final int getHeaderSize() {
return mHeaderLayout.getContentSize();
}

protected int getPullToRefreshScrollDuration() {
return SMOOTH_SCROLL_DURATION_MS;
}

protected int getPullToRefreshScrollDurationLonger() {
return SMOOTH_SCROLL_LONG_DURATION_MS;
}

protected FrameLayout getRefreshableViewWrapper() {
return mRefreshableViewWrapper;
}

/**
* Allows Derivative classes to handle the XML Attrs without creating a
* TypedArray themsevles
*
* @param a - TypedArray of PullToRefresh Attributes
*/
protected void handleStyledAttributes(TypedArray a) {
}

/**
* 判断是否触发了加载操作
* Implemented by derived class to return whether the View is in a state
* where the user can Pull to Refresh by scrolling from the end.
*
* @return true if the View is currently in the correct state (for example,
*         bottom of a ListView)
*/
protected abstract boolean isReadyForPullEnd();

/**
* 判断是否促发了刷新操作
* Implemented by derived class to return whether the View is in a state
* where the user can Pull to Refresh by scrolling from the start.
*
* @return true if the View is currently the correct state (for example, top
*         of a ListView)
*/
protected abstract boolean isReadyForPullStart();

/**
* Called by {@link #onRestoreInstanceState(Parcelable)} so that derivative
* classes can handle their saved instance state.
*
* @param savedInstanceState - Bundle which contains saved instance state.
*/
protected void onPtrRestoreInstanceState(Bundle savedInstanceState) {
}

/**
* Called by {@link #onSaveInstanceState()} so that derivative classes can
* save their instance state.
*
* @param saveState - Bundle to be updated with saved state.
*/
protected void onPtrSaveInstanceState(Bundle saveState) {
}

/**
* Called when the UI has been to be updated to be in the
* {@link State#PULL_TO_REFRESH} state.
*/
protected void onPullToRefresh() {
switch (mCurrentMode) {
case PULL_FROM_END:
mFooterLayout.pullToRefresh();
break;
case PULL_FROM_START:
mHeaderLayout.pullToRefresh();
break;
default:
// NO-OP
break;
}
}

/**
* Called when the UI has been to be updated to be in the
* {@link State#REFRESHING} or {@link State#MANUAL_REFRESHING} state.
*
* @param doScroll - Whether the UI should scroll for this event.
*/
protected void onRefreshing(final boolean doScroll) {
if (mMode.showHeaderLoadingLayout()) {
mHeaderLayout.refreshing();
}
if (mMode.showFooterLoadingLayout()) {
mFooterLayout.refreshing();
}

if (doScroll) {
if (mShowViewWhileRefreshing) {

// Call Refresh Listener when the Scroll has finished
OnSmoothScrollFinishedListener listener = new OnSmoothScrollFinishedListener() {
@Override
public void onSmoothScrollFinished() {
callRefreshListener();
}
};

switch (mCurrentMode) {
case MANUAL_REFRESH_ONLY:
case PULL_FROM_END:
smoothScrollTo(getFooterSize(), listener);
break;
default:
case PULL_FROM_START:
smoothScrollTo(-getHeaderSize(), listener);
break;
}
} else {
smoothScrollTo(0);
}
} else {
// We're not scrolling, so just call Refresh Listener now
callRefreshListener();
}
}

/**
* Called when the UI has been to be updated to be in the
* {@link State#RELEASE_TO_REFRESH} state.
*/
protected void onReleaseToRefresh() {
switch (mCurrentMode) {
case PULL_FROM_END:
mFooterLayout.releaseToRefresh();
break;
case PULL_FROM_START:
mHeaderLayout.releaseToRefresh();
break;
default:
// NO-OP
break;
}
}

/**
* Called when the UI has been to be updated to be in the
* {@link State#RESET} state.
*/
protected void onReset() {
mIsBeingDragged = false;
mLayoutVisibilityChangesEnabled = true;

// Always reset both layouts, just in case...
mHeaderLayout.reset();
mFooterLayout.reset();

smoothScrollTo(0);
}

@Override
protected final void onRestoreInstanceState(Parcelable state) {
if (state instanceof Bundle) {
Bundle bundle = (Bundle) state;

setMode(Mode.mapIntToValue(bundle.getInt(STATE_MODE, 0)));
mCurrentMode = Mode.mapIntToValue(bundle.getInt(STATE_CURRENT_MODE, 0));

mScrollingWhileRefreshingEnabled = bundle.getBoolean(STATE_SCROLLING_REFRESHING_ENABLED, false);
mShowViewWhileRefreshing = bundle.getBoolean(STATE_SHOW_REFRESHING_VIEW, true);

// Let super Restore Itself
super.onRestoreInstanceState(bundle.getParcelable(STATE_SUPER));

State viewState = State.mapIntToValue(bundle.getInt(STATE_STATE, 0));
if (viewState == State.REFRESHING || viewState == State.MANUAL_REFRESHING) {
setState(viewState, true);
}

// Now let derivative classes restore their state
onPtrRestoreInstanceState(bundle);
return;
}

super.onRestoreInstanceState(state);
}

@Override
protected final Parcelable onSaveInstanceState() {
Bundle bundle = new Bundle();

// Let derivative classes get a chance to save state first, that way we
// can make sure they don't overrite any of our values
onPtrSaveInstanceState(bundle);

bundle.putInt(STATE_STATE, mState.getIntValue());
bundle.putInt(STATE_MODE, mMode.getIntValue());
bundle.putInt(STATE_CURRENT_MODE, mCurrentMode.getIntValue());
bundle.putBoolean(STATE_SCROLLING_REFRESHING_ENABLED, mScrollingWhileRefreshingEnabled);
bundle.putBoolean(STATE_SHOW_REFRESHING_VIEW, mShowViewWhileRefreshing);
bundle.putParcelable(STATE_SUPER, super.onSaveInstanceState());

return bundle;
}

@Override
protected final void onSizeChanged(int w, int h, int oldw, int oldh) {
if (DEBUG) {
Log.d(LOG_TAG, String.format("onSizeChanged. W: %d, H: %d", w, h));
}

super.onSizeChanged(w, h, oldw, oldh);

// We need to update the header/footer when our size changes
refreshLoadingViewsSize();

// Update the Refreshable View layout
refreshRefreshableViewSize(w, h);

/**
* As we're currently in a Layout Pass, we need to schedule another one
* to layout any changes we've made here
*/
post(new Runnable() {
@Override
public void run() {
requestLayout();
}
});
}

/**
* Re-measure the Loading Views height, and adjust internal padding as
* necessary
*/
protected final void refreshLoadingViewsSize() {
final int maximumPullScroll = (int) (getMaximumPullScroll() * 1.2f);

int pLeft = getPaddingLeft();
int pTop = getPaddingTop();
int pRight = getPaddingRight();
int pBottom = getPaddingBottom();

switch (getPullToRefreshScrollDirection()) {
case HORIZONTAL:
if (mMode.showHeaderLoadingLayout()) {
mHeaderLayout.setWidth(maximumPullScroll);
pLeft = -maximumPullScroll;
} else {
pLeft = 0;
}

if (mMode.showFooterLoadingLayout()) {
mFooterLayout.setWidth(maximumPullScroll);
pRight = -maximumPullScroll;
} else {
pRight = 0;
}
break;

case VERTICAL:
if (mMode.showHeaderLoadingLayout()) {
mHeaderLayout.setHeight(maximumPullScroll);
pTop = -maximumPullScroll;
} else {
pTop = 0;
}

if (mMode.showFooterLoadingLayout()) {
mFooterLayout.setHeight(maximumPullScroll);
pBottom = -maximumPullScroll;
} else {
pBottom = 0;
}
break;
}

if (DEBUG) {
Log.d(LOG_TAG, String.format("Setting Padding. L: %d, T: %d, R: %d, B: %d", pLeft, pTop, pRight, pBottom));
}
setPadding(pLeft, pTop, pRight, pBottom);
}

protected final void refreshRefreshableViewSize(int width, int height) {
// We need to set the Height of the Refreshable View to the same as
// this layout
LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) mRefreshableViewWrapper.getLayoutParams();

switch (getPullToRefreshScrollDirection()) {
case HORIZONTAL:
if (lp.width != width) {
lp.width = width;
mRefreshableViewWrapper.requestLayout();
}
break;
case VERTICAL:
if (lp.height != height) {
lp.height = height;
mRefreshableViewWrapper.requestLayout();
}
break;
}
}

/**
* Helper method which just calls scrollTo() in the correct scrolling
* direction.
*  根据向下还是向上滑动来设置头部或尾部的显示，然后控件随手指滚动，这样头部或者尾部就显示出来
* @param value - New Scroll value  当前滚动的距离
*/
protected final void setHeaderScroll(int value) {
if (DEBUG) {
Log.d(LOG_TAG, "setHeaderScroll: " + value);
}

// Clamp value to with pull scroll range
final int maximumPullScroll = getMaximumPullScroll();
value = Math.min(maximumPullScroll, Math.max(-maximumPullScroll, value));

if (mLayoutVisibilityChangesEnabled) {
if (value < 0) {
mHeaderLayout.setVisibility(View.VISIBLE);
} else if (value > 0) {
mFooterLayout.setVisibility(View.VISIBLE);
} else {
mHeaderLayout.setVisibility(View.INVISIBLE);
mFooterLayout.setVisibility(View.INVISIBLE);
}
}

if (USE_HW_LAYERS) {
/**
* Use a Hardware Layer on the Refreshable View if we've scrolled at
* all. We don't use them on the Header/Footer Views as they change
* often, which would negate any HW layer performance boost.
*/
ViewCompat.setLayerType(mRefreshableViewWrapper, value != 0 ? View.LAYER_TYPE_HARDWARE
: View.LAYER_TYPE_NONE);
}

switch (getPullToRefreshScrollDirection()) {
case VERTICAL:
scrollTo(0, value);
break;
case HORIZONTAL:
scrollTo(value, 0);
break;
}
}

/**
* Smooth Scroll to position using the default duration of
* {@value #SMOOTH_SCROLL_DURATION_MS} ms.
*
* @param scrollValue - Position to scroll to
*/
protected final void smoothScrollTo(int scrollValue) {
smoothScrollTo(scrollValue, getPullToRefreshScrollDuration());
}

/**
* Smooth Scroll to position using the default duration of
* {@value #SMOOTH_SCROLL_DURATION_MS} ms.
*
* @param scrollValue - Position to scroll to
* @param listener - Listener for scroll
*/
protected final void smoothScrollTo(int scrollValue, OnSmoothScrollFinishedListener listener) {
smoothScrollTo(scrollValue, getPullToRefreshScrollDuration(), 0, listener);
}

/**
* Smooth Scroll to position using the longer default duration of
* {@value #SMOOTH_SCROLL_LONG_DURATION_MS} ms.
*
* @param scrollValue - Position to scroll to
*/
protected final void smoothScrollToLonger(int scrollValue) {
smoothScrollTo(scrollValue, getPullToRefreshScrollDurationLonger());
}

/**
*  在这里把头部和尾部 加载到自身LinearLayout上，并隐藏头部和尾部
* Updates the View State when the mode has been set. This does not do any
* checking that the mode is different to current state so always updates.
*/
protected void updateUIForMode() {
// We need to use the correct LayoutParam values, based on scroll
// direction
final LinearLayout.LayoutParams lp = getLoadingLayoutLayoutParams();

// Remove Header, and then add Header Loading View again if needed
if (this == mHeaderLayout.getParent()) {
removeView(mHeaderLayout);
}
if (mMode.showHeaderLoadingLayout()) {
addViewInternal(mHeaderLayout, 0, lp);
}

// Remove Footer, and then add Footer Loading View again if needed
if (this == mFooterLayout.getParent()) {
removeView(mFooterLayout);
}
if (mMode.showFooterLoadingLayout()) {
addViewInternal(mFooterLayout, lp);
}

// Hide Loading Views
refreshLoadingViewsSize();

// If we're not using Mode.BOTH, set mCurrentMode to mMode, otherwise
// set it to pull down
mCurrentMode = (mMode != Mode.BOTH) ? mMode : Mode.PULL_FROM_START;
}

private void addRefreshableView(Context context, T refreshableView) {
//把刷新加载View添加到FrameLayout上，然后将该FrameLayout 加载到自身LinearLayout上
//这个名叫mRefreshableViewWrapper 的FrameLayout就是刷新加载View的父View
mRefreshableViewWrapper = new FrameLayout(context);
mRefreshableViewWrapper.addView(refreshableView, ViewGroup.LayoutParams.MATCH_PARENT,
ViewGroup.LayoutParams.MATCH_PARENT);

addViewInternal(mRefreshableViewWrapper, new LinearLayout.LayoutParams(LayoutParams.MATCH_PARENT,
LayoutParams.MATCH_PARENT));
}

private void callRefreshListener() {
if (null != mOnRefreshListener) {
mOnRefreshListener.onRefresh(this);
} else if (null != mOnRefreshListener2) {
if (mCurrentMode == Mode.PULL_FROM_START) {
mOnRefreshListener2.onPullDownToRefresh(this);
} else if (mCurrentMode == Mode.PULL_FROM_END) {
mOnRefreshListener2.onPullUpToRefresh(this);
}
}
}

@SuppressWarnings("deprecation")
private void init(Context context, AttributeSet attrs) {
//  ①、获取刷新加载的方向
switch (getPullToRefreshScrollDirection()) {
case HORIZONTAL:
setOrientation(LinearLayout.HORIZONTAL);
break;
case VERTICAL:
default:
setOrientation(LinearLayout.VERTICAL);
break;
}

setGravity(Gravity.CENTER);

ViewConfiguration config = ViewConfiguration.get(context);
mTouchSlop = config.getScaledTouchSlop();

// Styleables from XML 【读取xml配置信息】
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.PullToRefresh);

// ②、获取配置的刷新加载模式
if (a.hasValue(R.styleable.PullToRefresh_ptrMode)) {
mMode = Mode.mapIntToValue(a.getInteger(R.styleable.PullToRefresh_ptrMode, 0));
}

if (a.hasValue(R.styleable.PullToRefresh_ptrAnimationStyle)) {
mLoadingAnimationStyle = AnimationStyle.mapIntToValue(a.getInteger(
R.styleable.PullToRefresh_ptrAnimationStyle, 0));
}

// Refreshable View
// By passing the attrs, we can add ListView/GridView params via XML
// ③、初始化刷新加载View
mRefreshableView = createRefreshableView(context, attrs);
// ④、将刷新加载View添加到布局
addRefreshableView(context, mRefreshableView);

// We need to create now layouts now
// ⑤、初始"刷新头部"和"加载外部"布局
mHeaderLayout = createLoadingLayout(context, Mode.PULL_FROM_START, a);
mFooterLayout = createLoadingLayout(context, Mode.PULL_FROM_END, a);

/**
* Styleables from XML
*/
if (a.hasValue(R.styleable.PullToRefresh_ptrRefreshableViewBackground)) {
Drawable background = a.getDrawable(R.styleable.PullToRefresh_ptrRefreshableViewBackground);
if (null != background) {
mRefreshableView.setBackgroundDrawable(background);
}
} else if (a.hasValue(R.styleable.PullToRefresh_ptrAdapterViewBackground)) {
Utils.warnDeprecation("ptrAdapterViewBackground", "ptrRefreshableViewBackground");
Drawable background = a.getDrawable(R.styleable.PullToRefresh_ptrAdapterViewBackground);
if (null != background) {
mRefreshableView.setBackgroundDrawable(background);
}
}

if (a.hasValue(R.styleable.PullToRefresh_ptrOverScroll)) {
mOverScrollEnabled = a.getBoolean(R.styleable.PullToRefresh_ptrOverScroll, true);
}

if (a.hasValue(R.styleable.PullToRefresh_ptrScrollingWhileRefreshingEnabled)) {
mScrollingWhileRefreshingEnabled = a.getBoolean(
R.styleable.PullToRefresh_ptrScrollingWhileRefreshingEnabled, false);
}

// Let the derivative classes have a go at handling attributes, then
// recycle them...
handleStyledAttributes(a);
a.recycle();

// Finally update the UI for the modes
// ⑥、根据刷新加载模式更新控件
updateUIForMode();
}

//// 如果已经到达该滚动的临界值了，由具体子view实现控制
private boolean isReadyForPull() {
switch (mMode) {
case PULL_FROM_START:
return isReadyForPullStart();
case PULL_FROM_END:
return isReadyForPullEnd();
case BOTH:
return isReadyForPullEnd() || isReadyForPullStart();
default:
return false;
}
}

/**
* Actions a Pull Event
*
* @return true if the Event has been handled, false if there has been no
*         change
*/
private void pullEvent() {
final int newScrollValue; // 滑动距离
final int itemDimension; // 头部或尾部的 厚度
final float initialMotionValue, lastMotionValue; //初始位置   最后位置

switch (getPullToRefreshScrollDirection()) {//初始位置   最后位置
case HORIZONTAL:
initialMotionValue = mInitialMotionX;
lastMotionValue = mLastMotionX;
break;
case VERTICAL:
default:
initialMotionValue = mInitialMotionY;
lastMotionValue = mLastMotionY;
break;
}

switch (mCurrentMode) { // 计算 滑动距离  获取  头部或尾部的 厚度
case PULL_FROM_END:
newScrollValue = Math.round(Math.max(initialMotionValue - lastMotionValue, 0) / FRICTION);
itemDimension = getFooterSize();
break;
case PULL_FROM_START:
default:
newScrollValue = Math.round(Math.min(initialMotionValue - lastMotionValue, 0) / FRICTION);
itemDimension = getHeaderSize();
break;
}

setHeaderScroll(newScrollValue);//根据向下还是向上滑动来设置头部或尾部的显示，然后控件随手指滚动，这样头部或者尾部就显示出来

// 当滑动距离大于头部或尾部大小的时候，设置状态为释放以刷新，这就是我们上面所说的刷新头部或尾部完全显示，这时候放开手指就可以触发刷新加载的回调
if (newScrollValue != 0 && !isRefreshing()) {
float scale = Math.abs(newScrollValue) / (float) itemDimension;
switch (mCurrentMode) {
case PULL_FROM_END:
mFooterLayout.onPull(scale);
break;
case PULL_FROM_START:
default:
mHeaderLayout.onPull(scale);
break;
}

if (mState != State.PULL_TO_REFRESH && itemDimension >= Math.abs(newScrollValue)) {
setState(State.PULL_TO_REFRESH);
} else if (mState == State.PULL_TO_REFRESH && itemDimension < Math.abs(newScrollValue)) {
setState(State.RELEASE_TO_REFRESH);
}
}
}

private LinearLayout.LayoutParams getLoadingLayoutLayoutParams() {
switch (getPullToRefreshScrollDirection()) {
case HORIZONTAL:
return new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT,
LinearLayout.LayoutParams.MATCH_PARENT);
case VERTICAL:
default:
return new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT,
LinearLayout.LayoutParams.WRAP_CONTENT);
}
}

private int getMaximumPullScroll() {
switch (getPullToRefreshScrollDirection()) {
case HORIZONTAL:
return Math.round(getWidth() / FRICTION);
case VERTICAL:
default:
return Math.round(getHeight() / FRICTION);
}
}

/**
* Smooth Scroll to position using the specific duration
*
* @param scrollValue - Position to scroll to
* @param duration - Duration of animation in milliseconds
*/
private final void smoothScrollTo(int scrollValue, long duration) {
smoothScrollTo(scrollValue, duration, 0, null);
}

private final void smoothScrollTo(int newScrollValue, long duration, long delayMillis,
OnSmoothScrollFinishedListener listener) {
if (null != mCurrentSmoothScrollRunnable) {
mCurrentSmoothScrollRunnable.stop();
}

final int oldScrollValue;
switch (getPullToRefreshScrollDirection()) {
case HORIZONTAL:
oldScrollValue = getScrollX();
break;
case VERTICAL:
default:
oldScrollValue = getScrollY();
break;
}

if (oldScrollValue != newScrollValue) {
if (null == mScrollAnimationInterpolator) {
// Default interpolator is a Decelerate Interpolator
mScrollAnimationInterpolator = new DecelerateInterpolator();
}
mCurrentSmoothScrollRunnable = new SmoothScrollRunnable(oldScrollValue, newScrollValue, duration, listener);

if (delayMillis > 0) {
postDelayed(mCurrentSmoothScrollRunnable, delayMillis);
} else {
post(mCurrentSmoothScrollRunnable);
}
}
}

private final void smoothScrollToAndBack(int y) {
smoothScrollTo(y, SMOOTH_SCROLL_DURATION_MS, 0, new OnSmoothScrollFinishedListener() {

@Override
public void onSmoothScrollFinished() {
smoothScrollTo(0, SMOOTH_SCROLL_DURATION_MS, DEMO_SCROLL_INTERVAL, null);
}
});
}

public static enum AnimationStyle {
/**
* This is the default for Android-PullToRefresh. Allows you to use any
* drawable, which is automatically rotated and used as a Progress Bar.
*/
ROTATE,

/**
* This is the old default, and what is commonly used on iOS. Uses an
* arrow image which flips depending on where the user has scrolled.
*/
FLIP;

static AnimationStyle getDefault() {
return ROTATE;
}

/**
* Maps an int to a specific mode. This is needed when saving state, or
* inflating the view from XML where the mode is given through a attr
* int.
*
* @param modeInt - int to map a Mode to
* @return Mode that modeInt maps to, or ROTATE by default.
*/
static AnimationStyle mapIntToValue(int modeInt) {
switch (modeInt) {
case 0x0:
default:
return ROTATE;
case 0x1:
return FLIP;
}
}
//默认提供了两种样式,圆圈和箭头
LoadingLayout createLoadingLayout(Context context, Mode mode, Orientation scrollDirection, TypedArray attrs) {
switch (this) {
case ROTATE:
default:
return new RotateLoadingLayout(context, mode, scrollDirection, attrs);
case FLIP:
return new FlipLoadingLayout(context, mode, scrollDirection, attrs);
}
}
}

public static enum Mode {

/**
* Disable all Pull-to-Refresh gesture and Refreshing handling
* 不允许刷新、加载
*/
DISABLED(0x0),

/**
* 从头部刷新
* Only allow the user to Pull from the start of the Refreshable View to
* refresh. The start is either the Top or Left, depending on the
* scrolling direction.
*/
PULL_FROM_START(0x1),

/**
* 从尾部加载
* Only allow the user to Pull from the end of the Refreshable View to
* refresh. The start is either the Bottom or Right, depending on the
* scrolling direction.
*/
PULL_FROM_END(0x2),

/**
* 刷新加载都支持
* Allow the user to both Pull from the start, from the end to refresh.
*/
BOTH(0x3),

/**
* 只允许手动刷新加载
* Disables Pull-to-Refresh gesture handling, but allows manually
* setting the Refresh state via
* {@link PullToRefreshBase#setRefreshing() setRefreshing()}.
*/
MANUAL_REFRESH_ONLY(0x4);

/**
* @deprecated Use {@link #PULL_FROM_START} from now on.
*/
public static Mode PULL_DOWN_TO_REFRESH = Mode.PULL_FROM_START;

/**
* @deprecated Use {@link #PULL_FROM_END} from now on.
*/
public static Mode PULL_UP_TO_REFRESH = Mode.PULL_FROM_END;

/**
* Maps an int to a specific mode. This is needed when saving state, or
* inflating the view from XML where the mode is given through a attr
* int.
*
* @param modeInt - int to map a Mode to
* @return Mode that modeInt maps to, or PULL_FROM_START by default.
*/
static Mode mapIntToValue(final int modeInt) {
for (Mode value : Mode.values()) {
if (modeInt == value.getIntValue()) {
return value;
}
}

// If not, return default
return getDefault();
}

static Mode getDefault() {
return PULL_FROM_START;
}

private int mIntValue;

// The modeInt values need to match those from attrs.xml
Mode(int modeInt) {
mIntValue = modeInt;
}

/**
* @return true if the mode permits Pull-to-Refresh
*/
boolean permitsPullToRefresh() {
return !(this == DISABLED || this == MANUAL_REFRESH_ONLY);
}

/**
* @return true if this mode wants the Loading Layout Header to be shown
*/
public boolean showHeaderLoadingLayout() {
return this == PULL_FROM_START || this == BOTH;
}

/**
* @return true if this mode wants the Loading Layout Footer to be shown
*/
public boolean showFooterLoadingLayout() {
return this == PULL_FROM_END || this == BOTH || this == MANUAL_REFRESH_ONLY;
}

int getIntValue() {
return mIntValue;
}

}

// ===========================================================
// Inner, Anonymous Classes, and Enumerations
// ===========================================================

/**
* Simple Listener that allows you to be notified when the user has scrolled
* to the end of the AdapterView. See (
* {@link PullToRefreshAdapterViewBase#setOnLastItemVisibleListener}.
*
* @author Chris Banes
*/
public static interface OnLastItemVisibleListener {

/**
* Called when the user has scrolled to the end of the list
*/
public void onLastItemVisible();

}

/**
* Listener that allows you to be notified when the user has started or
* finished a touch event. Useful when you want to append extra UI events
* (such as sounds). See (
* {@link PullToRefreshAdapterViewBase#setOnPullEventListener}.
*
* @author Chris Banes
*/
public static interface OnPullEventListener<V extends View> {

/**
* Called when the internal state has been changed, usually by the user
* pulling.
*
* @param refreshView - View which has had it's state change.
* @param state - The new state of View.
* @param direction - One of {@link Mode#PULL_FROM_START} or
*            {@link Mode#PULL_FROM_END} depending on which direction
*            the user is pulling. Only useful when <var>state</var> is
*            {@link State#PULL_TO_REFRESH} or
*            {@link State#RELEASE_TO_REFRESH}.
*/
public void onPullEvent(final PullToRefreshBase<V> refreshView, State state, Mode direction);

}

/**
* Simple Listener to listen for any callbacks to Refresh.
*
* @author Chris Banes
*/
public static interface OnRefreshListener<V extends View> {

/**
* onRefresh will be called for both a Pull from start, and Pull from
* end
*/
public void onRefresh(final PullToRefreshBase<V> refreshView);

}

/**
* An advanced version of the Listener to listen for callbacks to Refresh.
* This listener is different as it allows you to differentiate between Pull
* Ups, and Pull Downs.
*
* @author Chris Banes
*/
public static interface OnRefreshListener2<V extends View> {
// TODO These methods need renaming to START/END rather than DOWN/UP

/**
* onPullDownToRefresh will be called only when the user has Pulled from
* the start, and released.
*/
public void onPullDownToRefresh(final PullToRefreshBase<V> refreshView);

/**
* onPullUpToRefresh will be called only when the user has Pulled from
* the end, and released.
*/
public void onPullUpToRefresh(final PullToRefreshBase<V> refreshView);

}

public static enum Orientation {
VERTICAL, HORIZONTAL;
}

public static enum State {

/**
* 初始状态
* When the UI is in a state which means that user is not interacting
* with the Pull-to-Refresh function.
*/
RESET(0x0),

/**
* 正在拉，但拉的不够远，不足在释放后以触发刷新加载的状态
* When the UI is being pulled by the user, but has not been pulled far
* enough so that it refreshes when released.
*/
PULL_TO_REFRESH(0x1),

/**
* 正在拉，且拉足够够远，足以在释放后触发刷新加载的状态
* When the UI is being pulled by the user, and <strong>has</strong>
* been pulled far enough so that it will refresh when released.
*/
RELEASE_TO_REFRESH(0x2),

/**
* 刷新 or 加载中
* When the UI is currently refreshing, caused by a pull gesture.
*/
REFRESHING(0x8),

/**
* 刷新 or 加载中
* When the UI is currently refreshing, caused by a call to
* {@link PullToRefreshBase#setRefreshing() setRefreshing()}.
*/
MANUAL_REFRESHING(0x9),

/**
* When the UI is currently overscrolling, caused by a fling on the
* Refreshable View.
*/
OVERSCROLLING(0x10);

/**
* Maps an int to a specific state. This is needed when saving state.
*
* @param stateInt - int to map a State to
* @return State that stateInt maps to
*/
static State mapIntToValue(final int stateInt) {
for (State value : State.values()) {
if (stateInt == value.getIntValue()) {
return value;
}
}

// If not, return default
return RESET;
}

private int mIntValue;

State(int intValue) {
mIntValue = intValue;
}

int getIntValue() {
return mIntValue;
}
}

final class SmoothScrollRunnable implements Runnable {
private final Interpolator mInterpolator;
private final int mScrollToY;
private final int mScrollFromY;
private final long mDuration;
private OnSmoothScrollFinishedListener mListener;

private boolean mContinueRunning = true;
private long mStartTime = -1;
private int mCurrentY = -1;

public SmoothScrollRunnable(int fromY, int toY, long duration, OnSmoothScrollFinishedListener listener) {
mScrollFromY = fromY;
mScrollToY = toY;
mInterpolator = mScrollAnimationInterpolator;
mDuration = duration;
mListener = listener;
}

@Override
public void run() {

/**
* Only set mStartTime if this is the first time we're starting,
* else actually calculate the Y delta
*/
if (mStartTime == -1) {
mStartTime = System.currentTimeMillis();
} else {

/**
* We do do all calculations in long to reduce software float
* calculations. We use 1000 as it gives us good accuracy and
* small rounding errors
*/
long normalizedTime = (1000 * (System.currentTimeMillis() - mStartTime)) / mDuration;
normalizedTime = Math.max(Math.min(normalizedTime, 1000), 0);

final int deltaY = Math.round((mScrollFromY - mScrollToY)
* mInterpolator.getInterpolation(normalizedTime / 1000f));
mCurrentY = mScrollFromY - deltaY;
setHeaderScroll(mCurrentY);
}

// If we're not at the target Y, keep going...
if (mContinueRunning && mScrollToY != mCurrentY) {
ViewCompat.postOnAnimation(PullToRefreshBase.this, this);
} else {
if (null != mListener) {
mListener.onSmoothScrollFinished();
}
}
}

public void stop() {
mContinueRunning = false;
removeCallbacks(this);
}
}

static interface OnSmoothScrollFinishedListener {
void onSmoothScrollFinished();
}

}