ViewDragHelper实战 自己打造Drawerlayout

一、概述

中间拖了蛮长时间了，在上一篇我们介绍了

ViewDragHelper

，详情：ViewDragHelper完全解析，当然了，上一篇都是小示例的形式去演示代码功能，并不能给人一种实用的感觉。那么，本篇博客就准备实用

ViewDragHelper

来实现一个DrawerLayout的效果，当然了，大家也可以选择直接去看

Drawerlayout

的源码。相信侧滑大家肯定不陌生，网络上流传无数个版本，其实利用

ViewDragHelper

就能方便的写出比较不错的侧滑代码~

那么首先上个效果图：



ok，其实和DrawerLayout效果类似，当然不是完全的一致~~本篇的主要目的也是演示VDH的实战用法，大家在选择侧滑的时候还是建议使用

DrawerLayout

.

二、实战

(一)布局文件

首先看一下布局文件:

<com.zhy.learn.view.LeftDrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"                                   android:layout_width="match_parent"
android:id="@+id/id_drawerlayout"                                     android:layout_height="match_parent"
>

<!--content-->
<RelativeLayout
android:clickable="true"
android:layout_width="match_parent"
android:background="#44ff0000"
android:layout_height="match_parent">

<TextView
android:id="@+id/id_content_tv"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="hello world"
android:textSize="40sp"
android:layout_centerInParent="true"/>
</RelativeLayout>

<!--menu-->
<FrameLayout
android:id="@+id/id_container_menu"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
</FrameLayout>

</com.zhy.learn.view.LeftDrawerLayout>

ok，可以看到我们的LeftDrawerLayout里面一个是content，一个是menu~为了方便，我们就默认child0为content，child1为menu。

（二）LeftDrawerLayout

package com.zhy.learn.view;

import android.content.Context;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;

import com.zhy.util.common.L;

/**
* Created by zhy on 15/5/29.
*/
public class LeftDrawerLayout extends ViewGroup
{
private static final int MIN_DRAWER_MARGIN = 64; // dp
/**
* Minimum velocity that will be detected as a fling
*/
private static final int MIN_FLING_VELOCITY = 400; // dips per second

/**
* drawer离父容器右边的最小外边距
*/
private int mMinDrawerMargin;

private View mLeftMenuView;
private View mContentView;

private ViewDragHelper mHelper;
/**
* drawer显示出来的占自身的百分比
*/
private float mLeftMenuOnScrren;

public LeftDrawerLayout(Context context, AttributeSet attrs)
{
super(context, attrs);
//setup drawer's minMargin
final float density = getResources().getDisplayMetrics().density;
final float minVel = MIN_FLING_VELOCITY * density;
mMinDrawerMargin = (int) (MIN_DRAWER_MARGIN * density + 0.5f);

mHelper = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback()
{
@Override
public int clampViewPositionHorizontal(View child, int left, int dx)
{
int newLeft = Math.max(-child.getWidth(), Math.min(left, 0));
return newLeft;
}

@Override
public boolean tryCaptureView(View child, int pointerId)
{
L.e("tryCaptureView");
return child == mLeftMenuView;
}

@Override
public void onEdgeDragStarted(int edgeFlags, int pointerId)
{
L.e("onEdgeDragStarted");
mHelper.captureChildView(mLeftMenuView, pointerId);
}

@Override
public void onViewReleased(View releasedChild, float xvel, float yvel)
{
L.e("onViewReleased");
final int childWidth = releasedChild.getWidth();
float offset = (childWidth + releasedChild.getLeft()) * 1.0f / childWidth;
mHelper.settleCapturedViewAt(xvel > 0 || xvel == 0 && offset > 0.5f ? 0 : -childWidth, releasedChild.getTop());
invalidate();
}

@Override
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy)
{
final int childWidth = changedView.getWidth();
float offset = (float) (childWidth + left) / childWidth;
mLeftMenuOnScrren = offset;
//offset can callback here
changedView.setVisibility(offset == 0 ? View.INVISIBLE : View.VISIBLE);
invalidate();
}

@Override
public int getViewHorizontalDragRange(View child)
{
return mLeftMenuView == child ? child.getWidth() : 0;
}
});
//设置edge_left track
mHelper.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT);
//设置minVelocity
mHelper.setMinVelocity(minVel);
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
{
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);

setMeasuredDimension(widthSize, heightSize);

View leftMenuView = getChildAt(1);
MarginLayoutParams lp = (MarginLayoutParams)
leftMenuView.getLayoutParams();

final int drawerWidthSpec = getChildMeasureSpec(widthMeasureSpec,
mMinDrawerMargin + lp.leftMargin + lp.rightMargin,
lp.width);
final int drawerHeightSpec = getChildMeasureSpec(heightMeasureSpec,
lp.topMargin + lp.bottomMargin,
lp.height);
leftMenuView.measure(drawerWidthSpec, drawerHeightSpec);

View contentView = getChildAt(0);
lp = (MarginLayoutParams) contentView.getLayoutParams();
final int contentWidthSpec = MeasureSpec.makeMeasureSpec(
widthSize - lp.leftMargin - lp.rightMargin, MeasureSpec.EXACTLY);
final int contentHeightSpec = MeasureSpec.makeMeasureSpec(
heightSize - lp.topMargin - lp.bottomMargin, MeasureSpec.EXACTLY);
contentView.measure(contentWidthSpec, contentHeightSpec);

mLeftMenuView = leftMenuView;
mContentView = contentView;

}

@Override
protected void onLayout(boolean changed, int l, int t, int r, int b)
{
View menuView = mLeftMenuView;
View contentView = mContentView;

MarginLayoutParams lp = (MarginLayoutParams) contentView.getLayoutParams();
contentView.layout(lp.leftMargin, lp.topMargin,
lp.leftMargin + contentView.getMeasuredWidth(),
lp.topMargin + contentView.getMeasuredHeight());

lp = (MarginLayoutParams) menuView.getLayoutParams();

final int menuWidth = menuView.getMeasuredWidth();
int childLeft = -menuWidth + (int) (menuWidth * mLeftMenuOnScrren);
menuView.layout(childLeft, lp.topMargin, childLeft + menuWidth,
lp.topMargin + menuView.getMeasuredHeight());
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev)
{
boolean shouldInterceptTouchEvent = mHelper.shouldInterceptTouchEvent(ev);
return shouldInterceptTouchEvent;
}

@Override
public boolean onTouchEvent(MotionEvent event)
{
mHelper.processTouchEvent(event);
return true;
}

@Override
public void computeScroll()
{
if (mHelper.continueSettling(true))
{
invalidate();
}
}

public void closeDrawer()
{
View menuView = mLeftMenuView;
mLeftMenuOnScrren = 0.f;
mHelper.smoothSlideViewTo(menuView, -menuView.getWidth(), menuView.getTop());
}

public void openDrawer()
{
View menuView = mLeftMenuView;
mLeftMenuOnScrren = 1.0f;
mHelper.smoothSlideViewTo(menuView, 0, menuView.getTop());
}

@Override
protected LayoutParams generateDefaultLayoutParams()
{
return new MarginLayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
}

public LayoutParams generateLayoutParams(AttributeSet attrs)
{
return new MarginLayoutParams(getContext(), attrs);
}

protected LayoutParams generateLayoutParams(ViewGroup.LayoutParams p)
{
return new MarginLayoutParams(p);
}

}

哈，很少的代码就完成了我们的侧滑的编写，目测如果使用横向的LinearLayout代码更短。构造方法中，主要就是初始化我们的mDragHelper了，接下来onMeasure和onLayout都比较简单，onLayout也只是去将我们的menu设置到屏幕的左侧以至于不可见。

onInterceptTouchEvent

和

onTouchEvent

中都只需要简单的调用mDragHelper的方法。那么核心代码都在我们的ViewDragHelper.Callback的实例中了。注意一点：我们LeftDrawerLayout默认的LayoutParams为MarginLayoutParams，注意复写相关方法。

接下来就把注意力放到我们的Callback中，我尽可能的按照调用的逻辑来解释各个方法：

onEdgeDragStarted 如果你仔细的看过上篇，那么一定知道这个方法的回调位置；因为我们的View不可见，所以我们没有办法直接通过触摸到它来把menu设置为captureView，所以我们只能设置边界检测，当MOVE时回调onEdgeDragStarted时，我们直接通过captureChildView手动捕获。

tryCaptureView 那么既然我们手动捕获了，为什么还需要这个方法呢？主要是因为当Drawer拉出的时候，我们通过拖拽Drawer也能进行移动菜单。

clampViewPositionHorizontal 主要是移动的时候去控制控制范围，可以看到我们的

int newLeft = Math.max(-child.getWidth(), Math.min(left, 0));

一定>=-child.getWidth() && <=0 。

getViewHorizontalDragRange 为什么要复写，我们上篇已经描述过，返回captureView的移动范围。

onViewReleased 则是释放的时候触发的，我们计算当前显示的百分比，以及加速度来决定是否显示drawer，从代码可以看出，当

xvel > 0

||

xvel == 0 && offset > 0.5f

显示我们的菜单，其他情况隐藏。这里注意一点xvel的值只有大于我们设置的minVelocity才会出现大于0，如果小于我们设置的值则一直是0。

onViewPositionChanged 整个pos变化的过程中，我们计算offset保存，这里可以使用接口将offset回调出去，方便做动画。

ok，我们重写的所有方法描述完成了~那么博文主要内容也就结束了~哈~是不是 so easy ~!

呃，忘了MainActivity和Fragment的代码了~~按顺序贴

（三）LeftDrawerLayoutActivity

package com.imooc.testandroid;

import android.os.Bundle;
import android.support.v4.app.FragmentManager;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;

import com.zhy.learn.view.LeftDrawerLayout;

public class LeftDrawerLayoutActivity extends ActionBarActivity
{

private LeftMenuFragment mMenuFragment;
private LeftDrawerLayout mLeftDrawerLayout ;
private TextView mContentTv ;

@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_left_drawer_layout);

mLeftDrawerLayout = (LeftDrawerLayout) findViewById(R.id.id_drawerlayout);
mContentTv = (TextView) findViewById(R.id.id_content_tv);

FragmentManager fm = getSupportFragmentManager();
mMenuFragment = (LeftMenuFragment) fm.findFragmentById(R.id.id_container_menu);
if (mMenuFragment == null)
{
fm.beginTransaction().add(R.id.id_container_menu, mMenuFragment = new LeftMenuFragment()).commit();
}

mMenuFragment.setOnMenuItemSelectedListener(new LeftMenuFragment.OnMenuItemSelectedListener()
{
@Override
public void menuItemSelected(String title)
{
mLeftDrawerLayout.closeDrawer();
mContentTv.setText(title);
}
});

}

可以看到drawer使用了一个Fragment ~~

(四) LeftMenuFragment

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.ListFragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;

/**
* Created by zhy on 15/4/26.
*/
public class LeftMenuFragment extends ListFragment {

private static final int SIZE_MENU_ITEM = 3;

private MenuItem[] mItems = new MenuItem[SIZE_MENU_ITEM];

private LeftMenuAdapter mAdapter;

private LayoutInflater mInflater;

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

mInflater = LayoutInflater.from(getActivity());

MenuItem menuItem = null;
for (int i = 0; i < SIZE_MENU_ITEM; i++) {
menuItem = new MenuItem(getResources().getStringArray(R.array.array_left_menu)[i], false, R.drawable.music_36px, R.drawable.music_36px_light);
mItems[i] = menuItem;
}
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return super.onCreateView(inflater, container, savedInstanceState);
}

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
view.setBackgroundColor(0xffffffff);
setListAdapter(mAdapter = new LeftMenuAdapter(getActivity(), mItems));

}

@Override
public void onListItemClick(ListView l, View v, int position, long id) {
super.onListItemClick(l, v, position, id);

if (mMenuItemSelectedListener != null) {
mMenuItemSelectedListener.menuItemSelected(((MenuItem) getListAdapter().getItem(position)).text);
}
mAdapter.setSelected(position);
}

//选择回调的接口
public interface OnMenuItemSelectedListener {
void menuItemSelected(String title);
}
private OnMenuItemSelectedListener mMenuItemSelectedListener;

public void setOnMenuItemSelectedListener(OnMenuItemSelectedListener menuItemSelectedListener) {
this.mMenuItemSelectedListener = menuItemSelectedListener;
}
}

public class MenuItem
{

public MenuItem(String text, boolean isSelected, int icon, int iconSelected) {
this.text = text;
this.isSelected = isSelected;
this.icon = icon;
this.iconSelected = iconSelected;
}

boolean isSelected;
String text;
int icon;
int iconSelected;
}

/**
* Created by zhy on 15/4/26.
*/
public class LeftMenuAdapter extends ArrayAdapter<MenuItem> {

private LayoutInflater mInflater;

private int mSelected;

public LeftMenuAdapter(Context context, MenuItem[] objects) {
super(context, -1, objects);

mInflater = LayoutInflater.from(context);

}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

if (convertView == null) {
convertView = mInflater.inflate(R.layout.item_left_menu, parent, false);
}

ImageView iv = (ImageView) convertView.findViewById(R.id.id_item_icon);
TextView title = (TextView) convertView.findViewById(R.id.id_item_title);
title.setText(getItem(position).text);
iv.setImageResource(getItem(position).icon);
convertView.setBackgroundColor(Color.TRANSPARENT);

if (position == mSelected) {
iv.setImageResource(getItem(position).iconSelected);
convertView.setBackgroundColor(getContext().getResources().getColor(R.color.state_menu_item_selected));
}

return convertView;
}

public void setSelected(int position) {
this.mSelected = position;
notifyDataSetChanged();
}

}

贴了一大串，主要就是Fragment的代码，内部有个ListView，所以还有个Adapter，这个Fragment在之前的博文中出现过，搬过来而已。item的布局文件就是一个TextView和ImageView~~不贴了~~大家自己下载源码~

源码点击下载（导入方式注意看下ReadMe）

ok，到此结束~~hava a nice day ~~

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