Google示例SlidingTabsColors分析

/*
* Copyright 2013 The Android Open Source Project
*
* 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.example.android.slidingtabscolors;

import com.example.android.common.view.SlidingTabLayout;

import android.graphics.Color;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import java.util.ArrayList;
import java.util.List;

/**
* A basic sample which shows how to use {@link com.example.android.common.view.SlidingTabLayout}
* to display a custom {@link ViewPager} title strip which gives continuous feedback to the user
* when scrolling.
*/
public class SlidingTabsColorsFragment extends Fragment {

/**
* This class represents a tab to be displayed by {@link ViewPager} and it's associated
* {@link SlidingTabLayout}.
* 这个类代表了一个tab通过ViewPager去显示，它和SlidingTabLayout相关联
*/
static class SamplePagerItem {
private final CharSequence mTitle;//pager title
private final int mIndicatorColor;//pager indicator color
private final int mDividerColor;

SamplePagerItem(CharSequence title, int indicatorColor, int dividerColor) {
mTitle = title;
mIndicatorColor = indicatorColor;
mDividerColor = dividerColor;
}

/**
* @return A new {@link Fragment} to be displayed by a {@link ViewPager}
* 返回一个新的Fragment通过ViewPager去显示
*/
Fragment createFragment() {
return ContentFragment.newInstance(mTitle, mIndicatorColor, mDividerColor);
}

/**
* @return the title which represents this tab. In this sample this is used directly by
* {@link android.support.v4.view.PagerAdapter#getPageTitle(int)}
*/
CharSequence getTitle() {
return mTitle;
}

/**
* @return the color to be used for indicator on the {@link SlidingTabLayout}
*/
int getIndicatorColor() {
return mIndicatorColor;
}

/**
* @return the color to be used for right divider on the {@link SlidingTabLayout}
*/
int getDividerColor() {
return mDividerColor;
}
}

static final String LOG_TAG = "SlidingTabsColorsFragment";

/**
* A custom {@link ViewPager} title strip which looks much like Tabs present in Android v4.0 and
* above, but is designed to give continuous feedback to the user when scrolling.
*/
private SlidingTabLayout mSlidingTabLayout;

/**
* A {@link ViewPager} which will be used in conjunction with the {@link SlidingTabLayout} above.
*/
private ViewPager mViewPager;

/**
* List of {@link SamplePagerItem} which represent this sample's tabs.
*/
private List<SamplePagerItem> mTabs = new ArrayList<SamplePagerItem>();

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

// BEGIN_INCLUDE (populate_tabs)
/**
* Populate our tab list with tabs. Each item contains a title, indicator color and divider
* color, which are used by {@link SlidingTabLayout}.
* 使用我们的tab填充tabs列表，每个条目包含一个标题，指示器颜色，和分割线颜色
*/
mTabs.add(new SamplePagerItem(
getString(R.string.tab_stream), // Title
Color.BLUE, // Indicator color
Color.GRAY // Divider color
));

mTabs.add(new SamplePagerItem(
getString(R.string.tab_messages), // Title
Color.RED, // Indicator color
Color.GRAY // Divider color
));

mTabs.add(new SamplePagerItem(
getString(R.string.tab_photos), // Title
Color.YELLOW, // Indicator color
Color.GRAY // Divider color
));

mTabs.add(new SamplePagerItem(
getString(R.string.tab_notifications), // Title
Color.GREEN, // Indicator color
Color.GRAY // Divider color
));
// END_INCLUDE (populate_tabs)
}

/**
* Inflates the {@link View} which will be displayed by this {@link Fragment}, from the app's
* resources.
*/
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_sample, container, false);
}

// BEGIN_INCLUDE (fragment_onviewcreated)
/**
* This is called after the {@link #onCreateView(LayoutInflater, ViewGroup, Bundle)} has finished.
* Here we can pick out the {@link View}s we need to configure from the content view.
*
* We set the {@link ViewPager}'s adapter to be an instance of
* {@link SampleFragmentPagerAdapter}. The {@link SlidingTabLayout} is then given the
* {@link ViewPager} so that it can populate itself.
*
* @param view View created in {@link #onCreateView(LayoutInflater, ViewGroup, Bundle)}
*/
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
// BEGIN_INCLUDE (setup_viewpager)
// Get the ViewPager and set it's PagerAdapter so that it can display items
mViewPager = (ViewPager) view.findViewById(R.id.viewpager);
mViewPager.setAdapter(new SampleFragmentPagerAdapter(getChildFragmentManager()));
// END_INCLUDE (setup_viewpager)

// BEGIN_INCLUDE (setup_slidingtablayout)
// Give the SlidingTabLayout the ViewPager, this must be done AFTER the ViewPager has had
// it's PagerAdapter set.这必须在Viewpager的adapter被设置之后
mSlidingTabLayout = (SlidingTabLayout) view.findViewById(R.id.sliding_tabs);
mSlidingTabLayout.setViewPager(mViewPager);
mSlidingTabLayout.setCustomTextViewColor(Color.RED,Color.BLACK);

// BEGIN_INCLUDE (tab_colorizer)
// Set a TabColorizer to customize the indicator and divider colors. Here we just retrieve
// the tab at the position, and return it's set color
mSlidingTabLayout.setCustomTabColorizer(new SlidingTabLayout.TabColorizer() {

@Override
public int getIndicatorColor(int position) {
return mTabs.get(position).getIndicatorColor();
}

@Override
public int getDividerColor(int position) {
return mTabs.get(position).getDividerColor();
}

});
// END_INCLUDE (tab_colorizer)
// END_INCLUDE (setup_slidingtablayout)
}
// END_INCLUDE (fragment_onviewcreated)

/**
* The {@link FragmentPagerAdapter} used to display pages in this sample. The individual pages
* are instances of {@link ContentFragment} which just display three lines of text. Each page is
* created by the relevant {@link SamplePagerItem} for the requested position.
* <p>
* The important section of this class is the {@link #getPageTitle(int)} method which controls
* what is displayed in the {@link SlidingTabLayout}.
*/
class SampleFragmentPagerAdapter extends FragmentPagerAdapter {

SampleFragmentPagerAdapter(FragmentManager fm) {
super(fm);
}

/**
* Return the {@link android.support.v4.app.Fragment} to be displayed at {@code position}.
* <p>
* Here we return the value returned from {@link SamplePagerItem#createFragment()}.
*/
@Override
public Fragment getItem(int i) {
return mTabs.get(i).createFragment();
}

@Override
public int getCount() {
return mTabs.size();
}

// BEGIN_INCLUDE (pageradapter_getpagetitle)
/**
* Return the title of the item at {@code position}. This is important as what this method
* returns is what is displayed in the {@link SlidingTabLayout}.
* <p>
* Here we return the value returned from {@link SamplePagerItem#getTitle()}.
*/
@Override
public CharSequence getPageTitle(int position) {
return mTabs.get(position).getTitle();
}
// END_INCLUDE (pageradapter_getptle)

}

}

/*
* Copyright (C) 2013 The Android Open Source Project
*
* 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.example.android.common.view;

import android.content.Context;
import android.graphics.Color;
import android.graphics.Typeface;
import android.os.Build;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.HorizontalScrollView;
import android.widget.TextView;

import com.example.android.common.logger.Log;

/**
* To be used with ViewPager to provide a tab indicator component which give constant feedback as to
* the user's scroll progress.
* <p>
* To use the component, simply add it to your view hierarchy. Then in your
* {@link android.app.Activity} or {@link android.support.v4.app.Fragment} call
* {@link #setViewPager(ViewPager)} providing it the ViewPager this layout is being used for.
* <p>
* The colors can be customized in two ways. The first and simplest is to provide an array of colors
* via {@link #setSelectedIndicatorColors(int...)} and {@link #setDividerColors(int...)}. The
* alternative is via the {@link TabColorizer} interface which provides you complete control over
* which color is used for any individual position.
* <p>
* The views used as tabs can be customized by calling {@link #setCustomTabView(int, int)},
* providing the layout ID of your custom layout.
*
* just like list
*
* 本类作用：
* 将SlidingTabStrip作为子类添加到本类
* 在本类中根据PagerAdapter的大小生成TextView添加到SlidingTabStrip中，并设置TextView的点击监听和设置ViewPager.OnPageChangeListener监听器
* 在PageChange监听器中控制TextView的移动和调用SlidingTabStrip中的相应方法
*/
public class SlidingTabLayout extends HorizontalScrollView {

/**
* Allows complete control over the colors drawn in the tab layout. Set with
* {@link #setCustomTabColorizer(TabColorizer)}.
*/
public interface TabColorizer {

/**
* @return return the color of the indicator used when {@code position} is selected.
*/
int getIndicatorColor(int position);

/**
* @return return the color of the divider drawn to the right of {@code position}.
*/
int getDividerColor(int position);

}

private static final int TITLE_OFFSET_DIPS = 24;
// view padding
private static final int TAB_VIEW_PADDING_DIPS = 16;
// text size
private static final int TAB_VIEW_TEXT_SIZE_SP = 12;

private static final int TAB_VIEW_DEFAULT_TEXT_COLOR = Color.BLACK;

private int mTitleOffset;

private int mTabViewLayoutId;
private int mTabViewTextViewId;

private int mTabTextViewFocusColor;
private int mTabTextViewUnFocusColor;

private ViewPager mViewPager;
private ViewPager.OnPageChangeListener mViewPagerPageChangeListener;

private final SlidingTabStrip mTabStrip;

public SlidingTabLayout(Context context) {
this(context, null);
}

public SlidingTabLayout(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}

public SlidingTabLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);

// Disable the Scroll Bar
// Define whether the horizontal scrollbar should be drawn or not.
// The scrollbar is not drawn by default.
// 定义水平滚动栏是否应该被绘制
setHorizontalScrollBarEnabled(false);
// Make sure that the Tab Strips fills this View
// 表明这个HorizontalScrollView是否应该拉伸它的内容宽度去填充视图
setFillViewport(true);

mTitleOffset = (int) (TITLE_OFFSET_DIPS * getResources().getDisplayMetrics().density);

mTabStrip = new SlidingTabStrip(context);
//将mTabStrip添加到本容器中
addView(mTabStrip, LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
}

/**
* Set the custom {@link TabColorizer} to be used.
*
* If you only require simple custmisation then you can use
* {@link #setSelectedIndicatorColors(int...)} and {@link #setDividerColors(int...)} to achieve
* similar effects.
*
* set TabColorizer into SlidingTabStrip container
*/
public void setCustomTabColorizer(TabColorizer tabColorizer) {
mTabStrip.setCustomTabColorizer(tabColorizer);
}

/**
* Sets the colors to be used for indicating the selected tab. These colors are treated as a
* circular array. Providing one color will mean that all tabs are indicated with the same color.
*/
public void setSelectedIndicatorColors(int... colors) {
mTabStrip.setSelectedIndicatorColors(colors);
}

/**
* Sets the colors to be used for tab dividers. These colors are treated as a circular array.
* Providing one color will mean that all tabs are indicated with the same color.
*/
public void setDividerColors(int... colors) {
mTabStrip.setDividerColors(colors);
}

/**
* Set the {@link ViewPager.OnPageChangeListener}. When using {@link SlidingTabLayout} you are
* required to set any {@link ViewPager.OnPageChangeListener} through this method. This is so
* that the layout can update it's scroll position correctly.
*
* @see ViewPager#setOnPageChangeListener(ViewPager.OnPageChangeListener)
*
* 为本类中的监听器赋值
*/
public void setOnPageChangeListener(ViewPager.OnPageChangeListener listener) {
mViewPagerPageChangeListener = listener;
}

/**
* Set the custom layout to be inflated for the tab views.
*
* @param layoutResId Layout id to be inflated
* @param textViewId id of the {@link TextView} in the inflated view
*/
public void setCustomTabView(int layoutResId, int textViewId) {
mTabViewLayoutId = layoutResId;
mTabViewTextViewId = textViewId;
}

/**
*
* @param focusColor 焦点的颜色
* @param unfocusCilor 非焦点的颜色
*/
public void setCustomTextViewColor(int focusColor,int unfocusCilor){
mTabTextViewFocusColor = focusColor;
mTabTextViewUnFocusColor = unfocusCilor;
}

/**
* Sets the associated view pager. Note that the assumption here is that the pager content
* (number of tabs and tab titles) does not change after this call has been made.
* 注意调用这个方法后pager的内容没有改变
*
* remove all view in container and set listener for viewpager
*/
public void setViewPager(ViewPager viewPager) {
mTabStrip.removeAllViews();

mViewPager = viewPager;
if (viewPager != null) {
viewPager.setOnPageChangeListener(new InternalViewPagerListener());
populateTabStrip();
}
}

/**
* Create a default view to be used for tabs. This is called if a custom tab view is not set via
* {@link #setCustomTabView(int, int)}.
* 创建tabs使用的一个默认的TextView，如果没有通过setCustomTabView(int, int)设置一个自定义的tab view这将被调用
*/
protected TextView createDefaultTabView(Context context) {
TextView textView = new TextView(context);
textView.setGravity(Gravity.CENTER);
textView.setTextSize(TypedValue.COMPLEX_UNIT_SP, TAB_VIEW_TEXT_SIZE_SP);
textView.setTypeface(Typeface.DEFAULT_BOLD);

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
// If we're running on Honeycomb or newer, then we can use the Theme's
// selectableItemBackground to ensure that the View has a pressed state
// 如果我们运行在3.0或者以上的版本，那么我们可以使用主题的selectableItemBackground去确保View有一个按下的状态
TypedValue outValue = new TypedValue();
getContext().getTheme().resolveAttribute(android.R.attr.selectableItemBackground,
outValue, true);
textView.setBackgroundResource(outValue.resourceId);
}

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
// If we're running on ICS or newer, enable all-caps to match the Action Bar tab style
//如果我们运行在4.0或者4.0版本以上，Action Bar的tab的所有字母大写样式可用
textView.setAllCaps(true);
}

int padding = (int) (TAB_VIEW_PADDING_DIPS * getResources().getDisplayMetrics().density);
textView.setPadding(padding, padding, padding, padding);

return textView;
}

/**
* 根据PagerAdapter的数量，得到tabview并设置它的标题，设置监听器，添加到SlidingTabStrip中
*/
private void populateTabStrip() {
final PagerAdapter adapter = mViewPager.getAdapter();
final View.OnClickListener tabClickListener = new TabClickListener();

for (int i = 0; i < adapter.getCount(); i++) {
View tabView = null;
TextView tabTitleView = null;

//如果自定义的mTabViewLayoutId有值，则使用自定义的布局
if (mTabViewLayoutId != 0) {
// If there is a custom tab view layout id set, try and inflate it
// 如果这里有自定义的tab的视图布局id，尝试去填充它
tabView = LayoutInflater.from(getContext()).inflate(mTabViewLayoutId, mTabStrip,
false);
tabTitleView = (TextView) tabView.findViewById(mTabViewTextViewId);
}
//如果tabView没有赋值，则创建默认的TabView
if (tabView == null) {
tabView = createDefaultTabView(getContext());
}

if (tabTitleView == null && TextView.class.isInstance(tabView)) {
tabTitleView = (TextView) tabView;
}

//设置标题和监听器
tabTitleView.setText(adapter.getPageTitle(i));

tabView.setOnClickListener(tabClickListener);
//添加到SlidingTabStrip中
mTabStrip.addView(tabView);
}
}

/**
* This is called when the view is attached to a window.
* At this point it has a Surface and will start drawing.
* Note that this function is guaranteed to be called before onDraw(android.graphics.Canvas),
* however it may be called any time before the first onDraw --
* including before or after onMeasure(int, int)
*
* 当一个view被附着到window上的时候被调用。
*
* 注意这个功能被保证在onDraw(android.graphics.Canvas)之前调用，但是它可能在第一次onDraw方法之前的任何时候被调用
* 包括onMeasure(int, int)之前或者之后
*/
@Override
protected void onAttachedToWindow() {
super.onAttachedToWindow();

if (mViewPager != null) {
scrollToTab(mViewPager.getCurrentItem(), 0);
}
}

/**
* 控制TextView的滚动
* @param tabIndex
* @param positionOffset
*/
private void scrollToTab(int tabIndex, int positionOffset) {
final int tabStripChildCount = mTabStrip.getChildCount();
//不可以小于0 大于子类的数量
if (tabStripChildCount == 0 || tabIndex < 0 || tabIndex >= tabStripChildCount) {
return;
}

//得到当前的View
View selectedChild = mTabStrip.getChildAt(tabIndex);
if (selectedChild != null) {
int targetScrollX = selectedChild.getLeft() + positionOffset;

if (tabIndex > 0 || positionOffset > 0) {
// If we're not at the first child and are mid-scroll, make sure we obey the offset
// 如果我们不在第一个子类或者中间滚动，确定服从位移.mTitleOffset为24dp
targetScrollX -= mTitleOffset;
}

//为什么向左滚动滚动完成后才设置颜色，向右滚动开始滚动就已经开始设置颜色
//因为向左滚动的时候滚动完成position才变成position＋1，向右滚动开始滚动position就变成position－1了
if(positionOffset == 0)
setTabTextColor((TextView) selectedChild,tabIndex);

//滚动到指定的坐标位置
scrollTo(targetScrollX, 0);
}
}

/**
* 设置文本的颜色
*/
public void setTabTextColor(TextView selectedChild,int tabIndex){
if(mTabTextViewFocusColor == 0){
mTabTextViewFocusColor = TAB_VIEW_DEFAULT_TEXT_COLOR;
}
if(mTabTextViewUnFocusColor == 0){
mTabTextViewUnFocusColor = TAB_VIEW_DEFAULT_TEXT_COLOR;
}
selectedChild.setTextColor(mTabTextViewFocusColor);
for (int i = 0; i < mTabStrip.getChildCount(); i++) {
if(i != tabIndex){
TextView unfocusText = (TextView) mTabStrip.getChildAt(i);
unfocusText.setTextColor(mTabTextViewUnFocusColor);
}
}
}

/**
* 实现了OnPageChangeListener监听器
*/
private class InternalViewPagerListener implements ViewPager.OnPageChangeListener {
private int mScrollState;

@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
int tabStripChildCount = mTabStrip.getChildCount();
if ((tabStripChildCount == 0) || (position < 0) || (position >= tabStripChildCount)) {
return;
}

//ViewPager滚动的时候positionOffset值为0～1之间
mTabStrip.onViewPagerPageChanged(position, positionOffset);

View selectedTitle = mTabStrip.getChildAt(position);
//positionOffset如果从0～1表示向左滑，1～0表示向右滑
int extraOffset = (selectedTitle != null)
? (int) (positionOffset * selectedTitle.getWidth())
: 0;

scrollToTab(position, extraOffset);

if (mViewPagerPageChangeListener != null) {
mViewPagerPageChangeListener.onPageScrolled(position, positionOffset,
positionOffsetPixels);
}
}

@Override
public void onPageScrollStateChanged(int state) {
mScrollState = state;

if (mViewPagerPageChangeListener != null) {
mViewPagerPageChangeListener.onPageScrollStateChanged(state);
}
}

@Override
public void onPageSelected(int position) {
/**
* Indicates that the pager is in an idle, settled state.
* The current page is fully in view and no animation is in progress.
* 表明页面为空闲状态，停止状态，当前页面已经完全在view中，没有动画正在进行中
*/
if (mScrollState == ViewPager.SCROLL_STATE_IDLE) {
mTabStrip.onViewPagerPageChanged(position, 0f);
scrollToTab(position, 0);
}

if (mViewPagerPageChangeListener != null) {
mViewPagerPageChangeListener.onPageSelected(position);
}
}

}

/**
* tab click listener
*/
private class TabClickListener implements View.OnClickListener {
@Override
public void onClick(View v) {
for (int i = 0; i < mTabStrip.getChildCount(); i++) {
//judge which view is clicked
if (v == mTabStrip.getChildAt(i)) {
mViewPager.setCurrentItem(i);
return;
}
}
}
}

}

/*
* Copyright (C) 2013 The Android Open Source Project
*
* 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.example.android.common.view;

import android.R;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.View;
import android.widget.LinearLayout;

/**
* 本类作用：
* 绘制分割线，绘制底部指示器，绘制底部边界
*/
class SlidingTabStrip extends LinearLayout {

/**
* 默认底部边界的厚度（宽度）
*/
private static final int DEFAULT_BOTTOM_BORDER_THICKNESS_DIPS = 2;
/**
* 默认底部边界颜色的透明度
*/
private static final byte DEFAULT_BOTTOM_BORDER_COLOR_ALPHA = 0x26;
/**
* 已选指示器的厚度
*/
private static final int SELECTED_INDICATOR_THICKNESS_DIPS = 8;
/**
* 默认已选指示器的颜色
*/
private static final int DEFAULT_SELECTED_INDICATOR_COLOR = 0xFF33B5E5;
/**
* 默认分割线的厚度
*/
private static final int DEFAULT_DIVIDER_THICKNESS_DIPS = 1;
/**
* 默认分割线颜色的透明度
*/
private static final byte DEFAULT_DIVIDER_COLOR_ALPHA = 0x20;
/**
* 默认分割线的高度
*/
private static final float DEFAULT_DIVIDER_HEIGHT = 0.5f;
/**
* 底部边界的高度
*/
private final int mBottomBorderThickness;
/**
* 默认底部边界的画笔
*/
private final Paint mBottomBorderPaint;
/**
* 已选指示器的高度
*/
private final int mSelectedIndicatorThickness;
/**
* 已选指示器的画笔
*/
private final Paint mSelectedIndicatorPaint;
/**
* 默认底部边界的颜色
*/
private final int mDefaultBottomBorderColor;
/**
* 分割线的画笔
*/
private final Paint mDividerPaint;
/**
* 分割线的高度
*/
private final float mDividerHeight;
/**
* 选择的位置
*/
private int mSelectedPosition;
/**
* 选择的位移
*/
private float mSelectionOffset;
/**
* 自定义的Tab样式
*/
private SlidingTabLayout.TabColorizer mCustomTabColorizer;
/**
* 默认的Tab样式
*/
private final SimpleTabColorizer mDefaultTabColorizer;

SlidingTabStrip(Context context) {
this(context, null);
}

SlidingTabStrip(Context context, AttributeSet attrs) {
super(context, attrs);
//如果这个view不需要绘制任何东西，那么设置这个标志去允许进一步的优化
setWillNotDraw(false);

final float density = getResources().getDisplayMetrics().density;

//动态类型数据值的容器，主要被用于Resources去持有资源值
TypedValue outValue = new TypedValue();
context.getTheme().resolveAttribute(R.attr.colorForeground, outValue, true);
final int themeForegroundColor =  outValue.data;

//混合主题的前景颜色和默认的底部边界颜色的透明度，默认的底部边界颜色
mDefaultBottomBorderColor = setColorAlpha(themeForegroundColor,
DEFAULT_BOTTOM_BORDER_COLOR_ALPHA);

//默认的SimpleTabColorizer，指示器颜色为0xFF33B5E5，默认的分割线的颜色为主题的前景色和0x20混合的颜色
mDefaultTabColorizer = new SimpleTabColorizer();
mDefaultTabColorizer.setIndicatorColors(DEFAULT_SELECTED_INDICATOR_COLOR);
mDefaultTabColorizer.setDividerColors(setColorAlpha(themeForegroundColor,
DEFAULT_DIVIDER_COLOR_ALPHA));

//默认的底部高度
mBottomBorderThickness = (int) (DEFAULT_BOTTOM_BORDER_THICKNESS_DIPS * density);
mBottomBorderPaint = new Paint();
mBottomBorderPaint.setColor(mDefaultBottomBorderColor);

mSelectedIndicatorThickness = (int) (SELECTED_INDICATOR_THICKNESS_DIPS * density);
mSelectedIndicatorPaint = new Paint();

//分割先的高度和画笔
mDividerHeight = DEFAULT_DIVIDER_HEIGHT;
mDividerPaint = new Paint();
mDividerPaint.setStrokeWidth((int) (DEFAULT_DIVIDER_THICKNESS_DIPS * density));
}

/**
* 设置自定义的颜色样式并重绘
* @param customTabColorizer
*/
void setCustomTabColorizer(SlidingTabLayout.TabColorizer customTabColorizer) {
mCustomTabColorizer = customTabColorizer;
invalidate();
}

/**
* 设置已选的指示器颜色并重绘
* @param colors
*/
void setSelectedIndicatorColors(int... colors) {
// Make sure that the custom colorizer is removed
mCustomTabColorizer = null;
mDefaultTabColorizer.setIndicatorColors(colors);
invalidate();
}

/**
* 设置分割线的颜色
* @param colors
*/
void setDividerColors(int... colors) {
// Make sure that the custom colorizer is removed
mCustomTabColorizer = null;
mDefaultTabColorizer.setDividerColors(colors);
invalidate();
}

/**
* ViewPager页面改变的时候，传递的位置和位置偏移量
* @param position 向左滚动的时候滚动完成position才变成position＋1，向右滚动开始滚动position就变成position－1了
* @param positionOffset ViewPager页面改变的时候的positionOffset，如果从0～1表示向左滑，1～0表示向右滑
*/
void onViewPagerPageChanged(int position, float positionOffset) {
mSelectedPosition = position;
mSelectionOffset = positionOffset;
invalidate();
}

@Override
protected void onDraw(Canvas canvas) {
final int height = getHeight();
final int childCount = getChildCount();
final int dividerHeightPx = (int) (Math.min(Math.max(0f, mDividerHeight), 1f) * height);

// 如果自定义的TabColorizer为null，则选择默认的TabColorizer
final SlidingTabLayout.TabColorizer tabColorizer = mCustomTabColorizer != null
? mCustomTabColorizer
: mDefaultTabColorizer;

// Thick colored underline below the current selection
if (childCount > 0) {
View selectedTitle = getChildAt(mSelectedPosition);
int left = selectedTitle.getLeft();
int right = selectedTitle.getRight();
int color = tabColorizer.getIndicatorColor(mSelectedPosition);

//mSelectionOffset > 0f用于判断是否在移动
if (mSelectionOffset > 0f && mSelectedPosition < (getChildCount() - 1)) {
int nextColor = tabColorizer.getIndicatorColor(mSelectedPosition + 1);
//如果两个颜色不相同的话，混合颜色
if (color != nextColor) {
color = blendColors(nextColor, color, mSelectionOffset);
}

// Draw the selection partway between the tabs，得到下一个
View nextTitle = getChildAt(mSelectedPosition + 1);
// 计算指示器底部移动条的宽度，比如mSelectionOffset为0.7，就是0.7乘以后一个View的宽度加上0.3乘以前一个View的宽度
left = (int) (mSelectionOffset * nextTitle.getLeft() +
(1.0f - mSelectionOffset) * left);
right = (int) (mSelectionOffset * nextTitle.getRight() +
(1.0f - mSelectionOffset) * right);
}

mSelectedIndicatorPaint.setColor(color);

//绘制指示器底部的矩形
canvas.drawRect(left, height - mSelectedIndicatorThickness, right,
height, mSelectedIndicatorPaint);
}

// Thin underline along the entire bottom edge，底部一条长的分割线
canvas.drawRect(0, height - mBottomBorderThickness, getWidth(), height, mBottomBorderPaint);

// Vertical separators between the titles
int separatorTop = (height - dividerHeightPx) / 2;
// 绘制分割线
for (int i = 0; i < childCount - 1; i++) {
View child = getChildAt(i);
mDividerPaint.setColor(tabColorizer.getDividerColor(i));
canvas.drawLine(child.getRight(), separatorTop, child.getRight(),
separatorTop + dividerHeightPx, mDividerPaint);
}
}

/**
* Set the alpha value of the {@code color} to be the given {@code alpha} value.
* 使用argb (int alpha, int red, int green, int blue)方法生成一个新的颜色
*/
private static int setColorAlpha(int color, byte alpha) {
return Color.argb(alpha, Color.red(color), Color.green(color), Color.blue(color));
}

/**
* Blend {@code color1} and {@code color2} using the given ratio.
* 使用给定的比率混合color1和color2
*
* @param ratio of which to blend. 1.0 will return {@code color1}, 0.5 will give an even blend,
*              0.0 will return {@code color2}.
*/
private static int blendColors(int color1, int color2, float ratio) {
final float inverseRation = 1f - ratio;
//该算法实现渐变的效果
float r = (Color.red(color1) * ratio) + (Color.red(color2) * inverseRation);
float g = (Color.green(color1) * ratio) + (Color.green(color2) * inverseRation);
float b = (Color.blue(color1) * ratio) + (Color.blue(color2) * inverseRation);
return Color.rgb((int) r, (int) g, (int) b);
}

/**
* 实现了SlidingTabLayout.TabColorizer，保存指示器的颜色数组，分割线的颜色数组
*/
private static class SimpleTabColorizer implements SlidingTabLayout.TabColorizer {
private int[] mIndicatorColors;
private int[] mDividerColors;

/**
* 设计相当精妙，使用位置取余mIndicatorColors数组的长度，不用担心数组越界的情况
* @param position
* @return
*/
@Override
public final int getIndicatorColor(int position) {
return mIndicatorColors[position % mIndicatorColors.length];
}

@Override
public final int getDividerColor(int position) {
return mDividerColors[position % mDividerColors.length];
}

void setIndicatorColors(int... colors) {
mIndicatorColors = colors;
}

void setDividerColors(int... colors) {
mDividerColors = colors;
}
}
}