本篇主要介绍TabLayout在开发中一些常见的用法,不习惯简书代码风格的,也可以在 Android_Note查看.

TabLayout的默认样式:

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

从系统定义的该样式继续深入:

    <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">264dp</item>
        <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>

接着,看看系统定义Tab文本的样式(注意textAllcaps这个属性):

    <style name="TextAppearance.Design.Tab" parent="TextAppearance.AppCompat.Button">
        <item name="android:textSize">14dp</item>
        <item name="android:textColor">?android:textColorSecondary</item>
        <item name="textAllCaps">true</item>
    </style>

从系统定义TabLayout的默认样式可以看出,我们可以改变TabLayout对应的系统样式的属性值来适配我们自己的需求.

TabLayout的基本用法

TabLayout独立使用使用时,可以xml布局中静态添加tab个数及其样式,也可以动态添加Tab的个数及其样式,如:

     <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:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Android"/>

        <android.support.design.widget.TabItem
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:icon="@mipmap/ic_launcher"/>
    </android.support.design.widget.TabLayout>

这里写图片描述

或者:

    <android.support.design.widget.TabLayout
        android:id="@+id/tablayout"
        android:background="@color/colorPrimary"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    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);

这里写图片描述

TabLayout在实际开发中最多的是与ViewPager联合使用,实现TabLayout与ViewPager的联动:

    <android.support.design.widget.TabLayout
        android:id="@+id/tablayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/colorPrimary"
        app:tabGravity="fill"
        app:tabIndicatorColor="@android:color/holo_orange_dark"
        app:tabIndicatorHeight="2dp"
        app:tabMode="fixed"
        app:tabSelectedTextColor="@android:color/holo_orange_dark"
        app:tabTextAppearance="@style/CustomTabTextAppearanceStyle"
        app:tabTextColor="@android:color/white"
        app:theme="@style/Widget.Design.TabLayout"/>

    <android.support.v4.view.ViewPager
        android:id="@+id/view_pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

    TabLayout tabLayout = (TabLayout) findViewById(R.id.tablayout);
    ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
    viewPager.setAdapter(new TabPagerAdapter(getSupportFragmentManager()));
    tabLayout.setupWithViewPager(viewPager);

这里写图片描述

值得注意的是:

在TabPagerAdapter中需要实现getPagerTitle()否则,TabLayout的Tab将不显示,先看TabLayout#setupWithPager()源码,发现Tab的添加是在populateFromPagerAdapter()中实现,实现源码如下,可以看出该方法调用了PagerAdpater#getPagerTitle()为Tab设置文本信息,如果我们自定义的Adapter没有实现getPagerTitle()将会导致Tab不显示文本信息.

    void populateFromPagerAdapter() {
        removeAllTabs();

        if (mPagerAdapter != null) {
            final int adapterCount = mPagerAdapter.getCount();
            for (int i = 0; i < adapterCount; i++) {
                addTab(newTab().setText(mPagerAdapter.getPageTitle(i)), false);
            }

            // Make sure we reflect the currently set ViewPager item
            if (mViewPager != null && adapterCount > 0) {
                final int curItem = mViewPager.getCurrentItem();
                if (curItem != getSelectedTabPosition() && curItem < getTabCount()) {
                    selectTab(getTabAt(curItem));
                }
            }
        }
    }

另外, 我们发现getPagerTitle()方法的返回值CharSequence而不是String,那么Tab的文本信息的设置将变得更加灵活,比如设置一个SpanableString,将图片和文本设置Tab的文本.

        @Override
        public CharSequence getPageTitle(int position) {
            Drawable image = TablayoutActivity.this.getResources().getDrawable(images[position]);
            image.setBounds(0, 0, image.getIntrinsicWidth()/2, image.getIntrinsicHeight()/2);
            ImageSpan imageSpan = new ImageSpan(image, ImageSpan.ALIGN_BOTTOM);
            SpannableString ss = new SpannableString(" "+tabs[position]);
            ss.setSpan(imageSpan, 0, 1, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
            return ss;
        }   

但是Tab却没将image显示出来,从上面提到的TabLayout的系统默认样式中我们发现: <item name="textAllCaps">true</item>,这会阻止ImageSpan渲染出来,我们只需要将textAllCaps改为false即可,如下定义,再次运行,成功显示

    <style name="CustomTabTextAppearanceStyle" parent="TextAppearance.Design.Tab">
        <item name="textAllCaps">false</item>
    </style>

这里写图片描述

修改Indicator的长度:

从TabLayout的源码可以看出Indicator的绘制,是在其内部类SlidingTabStrip中绘制,而SlingTabStrip类继承LinearLayout,源码如下:

    @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);  
        }  
    }

在onDraw()中主要是就绘制一个Rect,并且宽度是根据mIndicatorLeft和mIndicatorRight设置的,而mIndicatorLeft等的宽度来自SlidingTabStrip的child,而Child就相当于一个Tab,这样我们就通过修改Child的margin来设置mIndicatorLeft的值.

    public void setIndicator(TabLayout tabs, int leftDip, int rightDip) {
        Class<?> tabLayout = tabs.getClass();
        Field tabStrip = null;
        try {
            tabStrip = tabLayout.getDeclaredField("mTabStrip");
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        }

        tabStrip.setAccessible(true);
        LinearLayout llTab = null;
        try {
            llTab = (LinearLayout) tabStrip.get(tabs);
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }

        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());

        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();
        }
    }

然后在代码中调用即可,但是要注意,必须要在Tablayout渲染出来后调用,我们可以选择view.post()方法来实现:

    tabLayout.post(new Runnable() {
            @Override
            public void run() {
                setIndicator(tabLayout, 20, 20);
            }
    });

最后得到效果图如下:

这里写图片描述

自定义TabLayout的TabItem及TabItem的点击事件

在TabLayout的Api是没有提供TabItem点击事件的方法,如果我们想实现如下效果图,怎么办?

这里写图片描述

先自定义一个TabItem:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="horizontal">

    <TextView
        android:id="@+id/txt_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:textSize="14sp" />

    <ImageView
        android:id="@+id/img_title"
        android:src="@drawable/indicator"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="5dp" />

</LinearLayout>

在自定义的Adapter中可以定义一个getTabView的方法:

    public View getTabView(int position){
        View view = LayoutInflater.from(context).inflate(R.layout.tab_item, null);
        TextView tv= (TextView) view.findViewById(R.id.textView);
        tv.setText(tabTitles[position]);
        ImageView img = (ImageView) view.findViewById(R.id.imageView);
        img.setImageResource(imageResId[position]);
        return view;
    }

重新设置点击事件:

    viewPager.setAdapter(pagerAdapter);
    tabLayout.setupWithViewPager(viewPager);
    for (int i = 0; i < tabLayout.getTabCount(); i++) {
        TabLayout.Tab tab = tabLayout.getTabAt(i);
        if (tab != null) {
            tab.setCustomView(pagerAdapter.getTabView(i));
            if (tab.getCustomView() != null) {
                View tabView = (View) tab.getCustomView().getParent();
                tabView.setTag(i);
                tabView.setOnClickListener(mTabOnClickListener);
            }
        }
    }
    viewPager.setCurrentItem(1);