java.lang.Object
   ?	android.view.View
 	   ?	android.view.ViewGroup
 	 	   ?	android.widget.FrameLayout
 	 	 	   ?	android.widget.HorizontalScrollView
 	 	 	 	   ?	android.support.design.widget.TabLayout

 <android.support.v4.view.ViewPager
     android:layout_width="match_parent"
     android:layout_height="match_parent">
     <android.support.design.widget.TabLayout
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_gravity="top" />
 </android.support.v4.view.ViewPager>

• onTabReselected(TabLayout.Tab tab)   Called when a tab that is already selected is chosen again by the user.
  
• onTabSelected(TabLayout.Tab tab)   Called when a tab enters the selected state.
  
• onTabUnselected(TabLayout.Tab tab)   Called when a tab exits the selected state.

public static class TabLayout.TabLayoutOnPageChangeListener extends Object implements ViewPager.OnPageChangeListener

• onPageScrollStateChanged(int state)   Called when the scroll state changes. Useful for discovering when the user begins dragging, when the pager is automatically settling to the current page, or when it is fully stopped/idle.
  
• onPageScrolled(int position, float positionOffset, int positionOffsetPixels)   This method will be invoked when the current page is scrolled, either as part of a programmatically initiated smooth scroll or a user initiated touch scroll.
  
• onPageSelected(int position)   This method will be invoked when a new page becomes selected. Animation is not necessarily complete.
  

public static class TabLayout.ViewPagerOnTabSelectedListener extends Object implements TabLayout.OnTabSelectedListener

• onTabReselected(TabLayout.Tab tab)   Called when a tab that is already selected is chosen again by the user.
  
• onTabSelected(TabLayout.Tab tab)   Called when a tab enters the selected state.
  
• onTabUnselected(TabLayout.Tab tab)   Called when a tab exits the selected state.
  

• android.support.design:tabBackground    Reference to a background to be applied to tabs. 
  
• android.support.design:tabContentStart    Position in the Y axis from the starting edge that tabs should be positioned from. 
  
• android.support.design:tabGravity    Gravity constant for tabs. 
  
• android.support.design:tabIndicatorColor / tabIndicatorHeight    Color of the indicator used to show the currently selected tab. 
• android.support.design:tabMaxWidth / tabMinWidth    The maximum width for tabs. 
• android.support.design:tabMode    The behavior mode for the Tabs in this layout
• android.support.design:tabPadding / tabPaddingBottom / ...    The preferred padding along all edges of tabs. 
• android.support.design:tabSelectedTextColor / tabTextColor    The text color to be applied to the currently selected tab. 
  
• android.support.design:tabTextAppearance    A reference to a TextAppearance style to be applied to tabs. 

• void    addOnTabSelectedListener(TabLayout.OnTabSelectedListener listener)   Add a TabLayout.OnTabSelectedListener that will be invoked when tab selection changes.
  
• void    removeOnTabSelectedListener(TabLayout.OnTabSelectedListener listener)   Remove the given TabLayout.OnTabSelectedListener that was previously added via addOnTabSelectedListener(OnTabSelectedListener).
  
• void    clearOnTabSelectedListeners()   Remove all previously added TabLayout.OnTabSelectedListeners.
  
• void    setOnTabSelectedListener(TabLayout.OnTabSelectedListener listener)   This method was deprecated in API level 24.0.0.
  

• void    addTab(TabLayout.Tab tab, boolean setSelected)   Add a tab to this layout. The tab will be added at the end of the list.
  
• void    addTab(TabLayout.Tab tab, int position)   Add a tab to this layout. The tab will be inserted at position. If this is the first tab to be added it will become the selected tab.
  
• void    addTab(TabLayout.Tab tab)   Add a tab to this layout. The tab will be added at the end of the list. If this is the first tab to be added it will become the selected tab.
  
• void    addTab(TabLayout.Tab tab, int position, boolean setSelected)
  
• void    removeAllTabs()   Remove all tabs from the action bar and deselect the current tab. 
  
• void    removeTabAt(int position)   Remove a tab from the layout. If the removed tab was selected it will be deselected and another tab will be selected if present.
  
• void    removeTab(TabLayout.Tab tab)   Remove a tab from the layout.

• TabLayout.Tab    getTabAt(int index)   Returns the tab at the specified index.
  
• TabLayout.Tab    newTab()   Create and return a new TabLayout.Tab.

• int    getSelectedTabPosition()   Returns the position of the current selected tab.
  
• int    getTabCount()   Returns the number of tabs currently registered with the action bar.

• void    addView(View child, int index)   Adds a child view. If no layout parameters are already set on the child, the default parameters for this ViewGroup are set on the child.
  
• void    addView(View child) 
  
• void    addView(View child, ViewGroup.LayoutParams params)   Adds a child view with the specified layout parameters.
  
• void    addView(View child, int index, ViewGroup.LayoutParams params)   Adds a child view with the specified layout parameters.

• void    setTabsFromPagerAdapter(PagerAdapter adapter)   This method was deprecated in API level 23.2.0. 
  

app:theme="@style/Widget.Design.TabLayout"

<style name="Widget.Design.TabLayout" parent="Base.Widget.Design.TabLayout">
	<item name="tabGravity">fill</item>
	<item name="tabMode">fixed</item>
</style>

<style name="Base.Widget.Design.TabLayout" parent="android:Widget">
	<item name="tabMaxWidth">@dimen/design_tab_max_width</item>【264dp】
	<item name="tabIndicatorColor">?attr/colorAccent</item>
	<item name="tabIndicatorHeight">2dp</item>
	<item name="tabPaddingStart">12dp</item>
	<item name="tabPaddingEnd">12dp</item>
	<item name="tabBackground">?attr/selectableItemBackground</item>
	<item name="tabTextAppearance">@style/TextAppearance.Design.Tab</item>
	<item name="tabSelectedTextColor">?android:textColorPrimary</item>
</style>

<style name="TextAppearance.Design.Tab" parent="TextAppearance.AppCompat.Button">
	<item name="android:textSize">@dimen/design_tab_text_size</item>
	<item name="android:textColor">?android:textColorSecondary</item>
	<item name="textAllCaps">true</item>【1、全部大写显示；2、可能导致无法显示某些内容】
</style>

 <android.support.design.widget.TabLayout
        android:id="@+id/tablayout"
        android:background="@color/colorPrimary"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <android.support.design.widget.TabItem
            android:text="Android"/>
        <android.support.design.widget.TabItem
            android:icon="@mipmap/ic_launcher"/>
</android.support.design.widget.TabLayout>

private int[] images = new int[]{
                    R.drawable.ic_account_balance_wallet_black,
                    R.drawable.ic_android_black,
                    R.drawable.ic_account_box_black};
private String[] tabs = new String[]{"小说", "电影", "相声"};
TabLayout tabLayout = (TabLayout) findViewById(R.id.tablayout);

tabLayout.addTab(tabLayout.newTab().setIcon(images[0]).setText(tabs[0]),true);
tabLayout.addTab(tabLayout.newTab().setIcon(images[1]).setText(tabs[1]),false);
tabLayout.addTab(tabLayout.newTab().setIcon(images[2]).setText(tabs[2]),false);

public void setupWithViewPager(@Nullable ViewPager viewPager) {
    setupWithViewPager(viewPager, true);
}

/**
 * The one-stop shop一站式服务 for setting up this {@link TabLayout} with a {@link ViewPager}.
 *
 * <p>This method will link the given ViewPager and this TabLayout together so that
 * changes in one are automatically reflected in the other. This includes scroll state changes and clicks.
 * The tabs displayed in this layout will be populated被填充 from the ViewPager adapter‘s page titles.</p>
 *
 * <p>If {@code autoRefresh} is {@code true}, any changes in the {@link PagerAdapter} will
 * trigger this layout to re-populate itself from the adapter‘s titles.</p>
 *
 * <p>If the given ViewPager is non-null, it needs to already have a {@link PagerAdapter} set.</p>
 *
 * @param viewPager   the ViewPager to link to, or {@code null} to clear any previous link
 * @param autoRefresh whether this layout should refresh its contents if the given ViewPager‘s content changes
 */
public void setupWithViewPager(@Nullable final ViewPager viewPager, boolean autoRefresh) {
    setupWithViewPager(viewPager, autoRefresh, false);
}

private void setupWithViewPager(@Nullable final ViewPager viewPager, boolean autoRefresh, boolean implicitSetup) {
    if (mViewPager != null) {
        // If we‘ve already been setup with a ViewPager, remove us from it
        if (mPageChangeListener != null)  mViewPager.removeOnPageChangeListener(mPageChangeListener);
        if (mAdapterChangeListener != null) mViewPager.removeOnAdapterChangeListener(mAdapterChangeListener);
    }
    if (mCurrentVpSelectedListener != null) {
        // If we already have a tab selected listener for the ViewPager, remove it
        removeOnTabSelectedListener(mCurrentVpSelectedListener);
        mCurrentVpSelectedListener = null;
    }
    if (viewPager != null) {
        mViewPager = viewPager;//上面清除的"mViewPager"相关的Listener都是我们上次绑定的"viewPager"
        // Add our custom OnPageChangeListener to the ViewPager
        if (mPageChangeListener == null) mPageChangeListener = new TabLayoutOnPageChangeListener(this);
        mPageChangeListener.reset();
        viewPager.addOnPageChangeListener(mPageChangeListener);
        // Now we‘ll add a tab selected listener to set ViewPager‘s current item
        mCurrentVpSelectedListener = new ViewPagerOnTabSelectedListener(viewPager);
        addOnTabSelectedListener(mCurrentVpSelectedListener);
        final PagerAdapter adapter = viewPager.getAdapter();
        if (adapter != null) {
            // Now we‘ll populate ourselves from the pager adapter, adding an observer if autoRefresh is enabled
            setPagerAdapter(adapter, autoRefresh);
        }
        // Add a listener so that we‘re notified of any adapter changes
        if (mAdapterChangeListener == null) mAdapterChangeListener = new AdapterChangeListener();
        mAdapterChangeListener.setAutoRefresh(autoRefresh);
        viewPager.addOnAdapterChangeListener(mAdapterChangeListener);
        // Now update the scroll position to match the ViewPager‘s current item
        setScrollPosition(viewPager.getCurrentItem(), 0f, true);
    } else {
        // We‘ve been given a null ViewPager so we need to clear out the internal state, listeners and observers
        mViewPager = null;
        setPagerAdapter(null, false);
    }
    mSetupViewPagerImplicitly = implicitSetup;
}

/**
 * 使用自定义的Tab，设置后要自己控制每个Tab的文字以及【默认】选中Tab的样式（比如默认第一个Tab要显示indicator等）
 */
private void setCustomTabView() {
	tabLayout.setSelectedTabIndicatorHeight(0);
	for (int i = 0; i < fragments.size(); i++) {//必须在setupWithViewPager之后（即被绑定VP的数据确定后）才可以操作
		View view = LayoutInflater.from(this).inflate(R.layout.item_tab, null);
		TextView tv_tab_name = (TextView) view.findViewById(R.id.tv_tab_name);
		View line_indicator = view.findViewById(R.id.line_indicator);
		tv_tab_name.setText(tabList.get(i));//控制每个Tab的文字
		if (i == 0) {//控制默认选中Tab的样式
			view.setSelected(true);//背景样式
			line_indicator.setSelected(true);//指示器样式
		} else {
			view.setSelected(false);
			line_indicator.setSelected(false);
		}
		TabLayout.Tab tab = tabLayout.getTabAt(i);//获得每一个tab
		if (tab != null) tab.setCustomView(view);//给每一个tab设置view
	}
}

/**
 * 添加监听，当使用自定义的Tab时，要自己控制选中Tab【改变】时Tab的样式，以及ViewPager的当前Item
 */
private void addOnTabSelectedListener() {
	tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
		@Override
		public void onTabSelected(TabLayout.Tab tab) {
			if (tab.getCustomView() != null) {
				tab.getCustomView().setSelected(true);//要自己控制选中Tab改变时Tab的样式
				tab.getCustomView().findViewById(R.id.line_indicator).setSelected(true);
				viewPager.setCurrentItem(tab.getPosition());//要自己控制ViewPager的当前Item
			}
		}
		@Override
		public void onTabUnselected(TabLayout.Tab tab) {
			if (tab.getCustomView() != null) {
				tab.getCustomView().setSelected(false);
				tab.getCustomView().findViewById(R.id.line_indicator).setSelected(false);
			}
		}
		@Override
		public void onTabReselected(TabLayout.Tab tab) {
		}
	});
}

@Override  
public void draw(Canvas canvas) {  
    super.draw(canvas);  
    // Thick colored underline below the current selection  
    if (mIndicatorLeft >= 0 && mIndicatorRight > mIndicatorLeft) {  
        canvas.drawRect(mIndicatorLeft, getHeight() - mSelectedIndicatorHeight,  
                mIndicatorRight, getHeight(), mSelectedIndicatorPaint);  
    }  
}

public static void setIndicator(TabLayout tabs, int leftDip, int rightDip) {
	try {
		Class<?> tabLayout = tabs.getClass();
		Field tabStrip = tabLayout.getDeclaredField("mTabStrip");
		tabStrip.setAccessible(true);
		int left = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, leftDip, Resources.getSystem().getDisplayMetrics());
		int right = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, rightDip, Resources.getSystem().getDisplayMetrics());
		LinearLayout llTab = (LinearLayout) tabStrip.get(tabs);
		for (int i = 0; i < llTab.getChildCount(); i++) {
			View child = llTab.getChildAt(i);
			child.setPadding(0, 0, 0, 0);
			LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(0, LinearLayout.LayoutParams.MATCH_PARENT, 1);
			params.leftMargin = left;
			params.rightMargin = right;
			child.setLayoutParams(params);
			child.invalidate();
		}
	} catch (Exception e) {
		e.printStackTrace();
	}
}

mTabLayout.post(() -> setIndicator(gifTab, padding, padding));//必须在setupWithViewPager之后（数据确定后）才可以操作