<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <RadioGroup
        android:id="@+id/rg_tab_bar"
        android:layout_width="match_parent"
        android:layout_height="56dp"
        android:layout_alignParentBottom="true"
        android:background="@color/bg_white"
        android:elevation="5dp"
        android:orientation="horizontal">

        <RadioButton
            android:id="@+id/rb_channel"
            style="@style/tab_menu_item"
            android:drawableTop="@drawable/tab_menu_doc"
            android:text="@string/tab_menu_doc" />

        <RadioButton
            android:id="@+id/rb_message"
            style="@style/tab_menu_item"
            android:drawableTop="@drawable/tab_menu_camera"
            android:text="@string/tab_menu_camera" />

        <RadioButton
            android:id="@+id/rb_better"
            style="@style/tab_menu_item"
            android:drawableTop="@drawable/tab_menu_user"
            android:text="@string/tab_menu_user" />


    </RadioGroup>

    <View
        android:id="@+id/div_tab_bar"
        android:layout_width="match_parent"
        android:layout_height="2px"
        android:layout_above="@id/rg_tab_bar"
        android:background="@color/div_white" />

    <android.support.v4.view.ViewPager
        android:id="@+id/vpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_above="@id/div_tab_bar" />
</RelativeLayout>

public class MainActivity extends AppCompatActivity implements RadioGroup.OnCheckedChangeListener,
        ViewPager.OnPageChangeListener {

    //UI Objects
    private RadioGroup rg_tab_bar;
    private RadioButton rb_channel;
    private RadioButton rb_message;
    private RadioButton rb_better;
    private ViewPager vpager;
    private MyFragmentPagerAdapter mAdapter;

    //几个代表页面的常量
    public static final int PAGE_ONE = 0;
    public static final int PAGE_TWO = 1;
    public static final int PAGE_THREE = 2;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mAdapter = new MyFragmentPagerAdapter(getSupportFragmentManager());
        bindViews();
        rb_channel.setChecked(true);
    }

    private void bindViews() {

        rg_tab_bar = (RadioGroup) findViewById(R.id.rg_tab_bar);
        rb_channel = (RadioButton) findViewById(R.id.rb_channel);
        rb_message = (RadioButton) findViewById(R.id.rb_message);
        rb_better = (RadioButton) findViewById(R.id.rb_better);
        rg_tab_bar.setOnCheckedChangeListener(this);
        vpager = (ViewPager) findViewById(R.id.vpager);
        vpager.setAdapter(mAdapter);
        vpager.setCurrentItem(0);
        vpager.addOnPageChangeListener(this);
    }

    @Override
    public void onCheckedChanged(RadioGroup group, int checkedId) {
        switch (checkedId) {
            case R.id.rb_channel:
                vpager.setCurrentItem(PAGE_ONE);
                break;
            case R.id.rb_message:
                vpager.setCurrentItem(PAGE_TWO);
                break;
            case R.id.rb_better:
                vpager.setCurrentItem(PAGE_THREE);
                break;
        }
    }


    //重写ViewPager页面切换的处理方法
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    }

    @Override
    public void onPageSelected(int position) {
    }

    @Override
    public void onPageScrollStateChanged(int state) {
        //state的状态有三个，0表示什么都没做，1正在滑动，2滑动完毕
        if (state == 2) {
            switch (vpager.getCurrentItem()) {
                case PAGE_ONE:
                    rb_channel.setChecked(true);
                    break;
                case PAGE_TWO:
                    rb_message.setChecked(true);
                    break;
                case PAGE_THREE:
                    rb_better.setChecked(true);
                    break;
            }
        }
    }
}

public class MyFragmentPagerAdapter extends FragmentPagerAdapter {

    private final int PAGER_COUNT = 3;
    private DocFRAG docFRAG = null;
    private CameraFRAG cameraFRAG = null;
    private UserFRAG userFRAG = null;

    public MyFragmentPagerAdapter(FragmentManager fm) {
        super(fm);
        docFRAG = new DocFRAG();
        cameraFRAG = new CameraFRAG();
        userFRAG = new UserFRAG();

    }

    @Override
    public int getCount() {
        return PAGER_COUNT;
    }

    @Override
    public Object instantiateItem(ViewGroup vg, int position) {
        return super.instantiateItem(vg, position);
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        System.out.println("position Destory" + position);
        super.destroyItem(container, position, object);
    }

    @Override
    public Fragment getItem(int position) {
        Fragment fragment = null;
        switch (position) {
            case MainActivity.PAGE_ONE:
                fragment = docFRAG;
                break;
            case MainActivity.PAGE_TWO:
                fragment = cameraFRAG;
                break;
            case MainActivity.PAGE_THREE:
                fragment = userFRAG;
                break;

        }
        return fragment;
    }
}