前言

在谷歌发布Android Design Support Library之前，app底部tab布局的实现方法就有很多种，其中有RadioGroup+FrameLayout、TabHost+Fragment、FragmentPagerAdapter+ViewPager等方法，虽然这些方法虽然能达到同样的效果，但我个人总觉得有些繁琐。然而，Google在2015的IO大会上，给开发者们带来了全新的Android Design Support Library，里面包含了许多新控件，这些新控件有许多是把以前的一些第三方开源库官方化，实现起来更为简便，简直是开发者的福音。其中的TabLayout控件让我想到了app底部的tab布局，而且TabLayout用法更加简单，为何不试试用TabLayout实现简单的实现呢？好了，话不多说，先看看效果：

是不是和以前的方法实现的效果一样呢？下面我们来看看怎么简单实现。

过程

因为TabLayout和ViewPager分别是属于design和v4包下的，所以我们先在app的build.gradle中添加：

compile 'com.android.support:design:23.1.1'
compile 'com.android.support:support-v4:23.1.1'

然后在主布局文件activity_main.xml中添加布局控件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <android.support.v4.view.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:scrollbars="none">
    </android.support.v4.view.ViewPager>

    <android.support.design.widget.TabLayout
        android:id="@+id/tabLayout"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        app:tabGravity="fill"
        app:tabIndicatorHeight="0dp"
        app:tabMode="fixed"
        app:tabSelectedTextColor="#FF4081"
        app:tabTextColor="#000">
    </android.support.design.widget.TabLayout>

</LinearLayout>

就仅一个ViewPager和TabLayout就可以实现，是不是比以前的方法繁琐的布局简便很多？上面TabLayout中app:tabIndicatorHeight="0dp"是为了不显示tab底部的横线，app:tabMode="fixed"是让底部tab布局不可滑动。

接下来就和往常一样在MainActivity.java中初始化布局，设置适配器：

    private void initViews() {

        mTablayout= (TabLayout) findViewById(R.id.tabLayout);
        mViewPager= (ViewPager) findViewById(R.id.viewPager);

        mViewPager.setAdapter(new FragmentPagerAdapter(getSupportFragmentManager()) {

            private String[] mTitles = new String[]{"唐僧", "大师兄", "二师兄","沙师弟"};

            @Override
            public Fragment getItem(int position) {
                if (position == 1) {
                    return new TwoFragment();
                } else if (position == 2) {
                    return new ThreeFragment();
                }else if (position==3){
                    return new FourFragment();
                }
                return new OneFragment();
            }

            @Override
            public int getCount() {
                return mTitles.length;
            }

            @Override
            public CharSequence getPageTitle(int position) {
                return mTitles[position];
            }

        });

        mTablayout.setupWithViewPager(mViewPager);

        one = mTablayout.getTabAt(0);
        two = mTablayout.getTabAt(1);
        three = mTablayout.getTabAt(2);
        four = mTablayout.getTabAt(3);

        one.setIcon(getResources().getDrawable(R.drawable.ic_favorite_black_18dp));
        two.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));
        three.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));
        four.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));

    }

上面要注意的地方是别忘了在FragmentPagerAdapter中手动添加：

            @Override
            public CharSequence getPageTitle(int position) {
                return mTitles[position];
            }

不然不显示底部的文字。
mTablayout.setupWithViewPager(mViewPager);将TabLayout和ViewPager关联起来。
one = mTablayout.getTabAt(0);获取底部单个tab，用来添加初始化图片，注意下标都是从0开始的。

初始化监听事件

    private void initEvents() {

        mTablayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                if (tab == mTablayout.getTabAt(0)) {
                    one.setIcon(getResources().getDrawable(R.drawable.ic_favorite_black_18dp));
                    mViewPager.setCurrentItem(0);
                } else if (tab == mTablayout.getTabAt(1)) {
                    two.setIcon(getResources().getDrawable(R.drawable.ic_favorite_black_18dp));
                    mViewPager.setCurrentItem(1);
                } else if (tab == mTablayout.getTabAt(2)) {
                    three.setIcon(getResources().getDrawable(R.drawable.ic_favorite_black_18dp));
                    mViewPager.setCurrentItem(2);
                }else if (tab == mTablayout.getTabAt(3)){
                    four.setIcon(getResources().getDrawable(R.drawable.ic_favorite_black_18dp));
                    mViewPager.setCurrentItem(3);
                }

            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab) {
                if (tab == mTablayout.getTabAt(0)) {
                    one.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));
                } else if (tab == mTablayout.getTabAt(1)) {
                    two.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));
                } else if (tab == mTablayout.getTabAt(2)) {
                    three.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));
                }else if (tab == mTablayout.getTabAt(3)){
                    four.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));
                }
            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {

            }
        });

    }

在onTabSelected中设置选中tab时切换的图片，onTabUnselected中设置没有被选中时的图片。别忘了mViewPager.setCurrentItem(0);这句，这是用来点击tab时切换ViewPager，如果不加这一句的话滑动ViewPager底部tab可以切换，但是点击tab而ViewPager不会切换。

Fragment中的简单布局

fragment_one.xml

<?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:orientation="vertical">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="唐僧"
        android:layout_marginTop="100dp"
        android:layout_gravity="center"
        android:textSize="30sp"/>

</LinearLayout>

OneFragment.java

public class OneFragment extends Fragment{

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_one,container,false);
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
    }
}

MainActivity.java完整代码：

public class MainActivity extends AppCompatActivity {

    private TabLayout mTablayout;
    private ViewPager mViewPager;

    private TabLayout.Tab one;
    private TabLayout.Tab two;
    private TabLayout.Tab three;
    private TabLayout.Tab four;

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

        initViews();
        initEvents();
    }

    private void initEvents() {

        mTablayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                if (tab == mTablayout.getTabAt(0)) {
                    one.setIcon(getResources().getDrawable(R.drawable.ic_favorite_black_18dp));
                    mViewPager.setCurrentItem(0);
                } else if (tab == mTablayout.getTabAt(1)) {
                    two.setIcon(getResources().getDrawable(R.drawable.ic_favorite_black_18dp));
                    mViewPager.setCurrentItem(1);
                } else if (tab == mTablayout.getTabAt(2)) {
                    three.setIcon(getResources().getDrawable(R.drawable.ic_favorite_black_18dp));
                    mViewPager.setCurrentItem(2);
                }else if (tab == mTablayout.getTabAt(3)){
                    four.setIcon(getResources().getDrawable(R.drawable.ic_favorite_black_18dp));
                    mViewPager.setCurrentItem(3);
                }

            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab) {
                if (tab == mTablayout.getTabAt(0)) {
                    one.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));
                } else if (tab == mTablayout.getTabAt(1)) {
                    two.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));
                } else if (tab == mTablayout.getTabAt(2)) {
                    three.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));
                }else if (tab == mTablayout.getTabAt(3)){
                    four.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));
                }
            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {

            }
        });

    }

    private void initViews() {

        mTablayout= (TabLayout) findViewById(R.id.tabLayout);
        mViewPager= (ViewPager) findViewById(R.id.viewPager);

        mViewPager.setAdapter(new FragmentPagerAdapter(getSupportFragmentManager()) {

            private String[] mTitles = new String[]{"唐僧", "大师兄", "二师兄","沙师弟"};

            @Override
            public Fragment getItem(int position) {
                if (position == 1) {
                    return new TwoFragment();
                } else if (position == 2) {
                    return new ThreeFragment();
                }else if (position==3){
                    return new FourFragment();
                }
                return new OneFragment();
            }

            @Override
            public int getCount() {
                return mTitles.length;
            }

            @Override
            public CharSequence getPageTitle(int position) {
                return mTitles[position];
            }

        });

        mTablayout.setupWithViewPager(mViewPager);

        one = mTablayout.getTabAt(0);
        two = mTablayout.getTabAt(1);
        three = mTablayout.getTabAt(2);
        four = mTablayout.getTabAt(3);

        one.setIcon(getResources().getDrawable(R.drawable.ic_favorite_black_18dp));
        two.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));
        three.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));
        four.setIcon(getResources().getDrawable(R.mipmap.ic_launcher));

    }
}

结束语

以上就是简单用TabLayout+ViewPager实现app底部Tab布局的整个过程，如果你有更好的方法，或者文章中存在错误或不足的地方，欢迎在文章下面评论交流！