Android（ViewPager中的ViewPager）ViewPager FragmentPagerAdapter嵌套子ViewPager FragmentPagerAdapter页面不能正常显示

Android（ViewPager中的ViewPager）ViewPager FragmentPagerAdapter嵌套子ViewPager FragmentPagerAdapter页面不能正常显示问题

Android的ViewPager如果只使用一“层” FragmentPagerAdapter构建ViewPager，那么将不会导致本文题目中所说的问题，当ViewPager再次嵌套一个ViewPager时候，如果细节地方使用不当将导致页面不能正常显示问题。

比如，如图所示：

这是一个典型的ViewPager嵌套ViewPager的框架布局。底部0,1,2,3是一个SlidingTabLayout，SlidingTabLayout，SlidingTabLayout上面是一个ViewPager，其布局文件代码：

<RelativeLayout
        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" >

        <android.support.v4.view.ViewPager
            android:id="@+id/viewPager"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_above="@+id/slidingTabLayout" />

        <zhangphil.viewpagerdebug.SlidingTabLayout
            android:id="@+id/slidingTabLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"/>
            
</RelativeLayout>

Java代码：

package zhangphil.viewpagerdebug;

import java.util.ArrayList;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;


public class MainActivity extends FragmentActivity {

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

		setContentView(R.layout.activity_main);

		MyViewPagerAdapter adapter = new MyViewPagerAdapter(this.getSupportFragmentManager());
		ViewPager viewPager = (ViewPager) findViewById(R.id.viewPager);
		viewPager.setAdapter(adapter);

		SlidingTabLayout mSlidingTabLayout = (SlidingTabLayout) findViewById(R.id.slidingTabLayout);
		mSlidingTabLayout.setViewPager(viewPager);
	}

	private class MyViewPagerAdapter extends FragmentPagerAdapter {

		private ArrayList<Fragment> fragments;

		public MyViewPagerAdapter(FragmentManager fm) {
			super(fm);
			fragments = new ArrayList<Fragment>();
			for (int i = 0; i < 4; i++) {
				PageFragment f=new PageFragment();
				fragments.add(f);
			}
		}

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

		@Override
		public Fragment getItem(int pos) {
			return fragments.get(pos);
		}

		@Override
		public CharSequence getPageTitle(int pos) {
			return "" + pos;
		}
	}
}

将ViewPager与SlidingTabLayout联结起来。在此ViewPager中的MyViewPagerAdapter中喂给每一个ViewPager的子page又一个ViewPager——也是如果使用不当将引起问题的PageFragment：

package zhangphil.viewpagerdebug;

import java.util.ArrayList;

import android.os.Bundle;
import android.support.design.widget.TabLayout;
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;


public class PageFragment extends Fragment {

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

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

		TabLayout tabLayout = (TabLayout) view.findViewById(R.id.tabLayout);
		tabLayout.setSmoothScrollingEnabled(true);

		MyViewPagerAdapter pagerAdapter = new MyViewPagerAdapter(this.getChildFragmentManager());
		ViewPager viewPager = (ViewPager) view.findViewById(R.id.viewpager);
		viewPager.setAdapter(pagerAdapter);
		
		tabLayout.setupWithViewPager(viewPager);
	}

	private class MyViewPagerAdapter extends FragmentPagerAdapter {

		private ArrayList<Fragment> fragments;
		
		public MyViewPagerAdapter(FragmentManager fm) {
			super(fm);
			fragments = new ArrayList<Fragment>();
			for (int i = 0; i < 5; i++) {
				Fragment f=new ContentFragment();
				fragments.add(f);
			}
		}

		@Override
		public String getPageTitle(int pos) {
			return "卡" + pos;
		}

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

		@Override
		public Fragment getItem(int pos) {
			return	fragments.get(pos);
		}
	}
}

PageFragment的布局：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto" 
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <android.support.design.widget.TabLayout
        android:id="@+id/tabLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        app:tabGravity="fill"
        app:tabMode="fixed" >
    </android.support.design.widget.TabLayout>

     <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/tabLayout"
        android:layout_alignParentBottom="true" />
    
</RelativeLayout>

PageFragment就是图中顶部的卡0，卡1，卡2，卡3，卡4分别显示的每一个page。ContentFragment只是一个继承自ListFragment的、仅仅显示一行数据的演示Fragment。
PageFragment作为第二层、第二级ViewPager（ViewPager中的ViewPager）在PageFragment中创建此PageFragment的FragmentPagerAdapter时候，切记要传递给FragmentPagerAdapter的构造函数参数FragmentManager为：getChildFragmentManager() 而不是像父ViewPager中
那样直接随意的直接getFragmentManager()。如果PageFragment直接仍然用getFragmentManager()构造其FragmentPagerAdapter，将导致第二层、第二级的ViewPager不能正常显示。切记切记！