在Android中添加ViewPager in Fragment

Question

我有兩個片段：FirstFragment和SecondFragment。 FirstFragment包含ViewPager，它有三個頁面（三個片段）。在活動的onCreate，在主佈局上添加FirstFragment，3頁正常顯示。

問題是：當我用SecondFragment替換FirstFragment，然後復出FirstFragment三頁消失。然後我滾動ViewPager前進和後退，頁面顯示但只有第一和第三頁顯示，第二頁消失。

這裏FirstFragment：

package com.example.bkmsx.afragment; 
 

 
import android.os.Bundle; 
 
import android.support.annotation.Nullable; 
 
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 FirstFragment extends Fragment { 
 
    ViewPager mViewPager; 
 
    static MainActivity mainActivity; 
 
    public static FirstFragment newInstance(MainActivity activity){ 
 
     mainActivity = activity; 
 
     return new FirstFragment(); 
 
    } 
 
    @Nullable 
 
    @Override 
 
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) { 
 
     View view = inflater.inflate(R.layout.first_fragment, null); 
 
     mViewPager = (ViewPager) view.findViewById(R.id.view_pager); 
 
     ViewPagerAdapter adapter = new ViewPagerAdapter(mainActivity.getSupportFragmentManager()); 
 
     mViewPager.setAdapter(adapter); 
 
     return view; 
 
    } 
 

 
    private class ViewPagerAdapter extends FragmentPagerAdapter { 
 
     public ViewPagerAdapter(FragmentManager fm) { 
 
      super(fm); 
 
     } 
 

 
     @Override 
 
     public Fragment getItem(int position) { 
 
      String text = ""; 
 
      switch (position) { 
 
       case 0: text = "First Page"; 
 
        break; 
 
       case 1: text = "Second Page"; 
 
        break; 
 
       case 2: text = "Third Page"; 
 
        break; 
 
      } 
 
      return TextFragment.newInstance(mainActivity, text); 
 
     } 
 

 
     @Override 
 
     public int getCount() { 
 
      return 3; 
 
     } 
 
    } 
 
}

SecondFragment：

package com.example.bkmsx.afragment; 
 

 
import android.os.Bundle; 
 
import android.support.annotation.Nullable; 
 
import android.support.v4.app.Fragment; 
 
import android.view.LayoutInflater; 
 
import android.view.View; 
 
import android.view.ViewGroup; 
 
import android.widget.TextView; 
 

 
public class SecondFragment extends Fragment { 
 
    static MainActivity mainActivity; 
 

 
    public static SecondFragment newInstance(MainActivity activity) { 
 
     mainActivity = activity; 
 
     return new SecondFragment(); 
 
    } 
 
    @Nullable 
 
    @Override 
 
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 
 
     TextView textView = new TextView(mainActivity); 
 
     textView.setText("New Fragment"); 
 
     return textView; 
 
    } 
 
}

任何sugg estion？提前致謝。

Answer 1

在FirstFragment，使用此代碼，並嘗試

public View view; // declare view as global variable 

@Nullable 
    @Override 
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) { 
     if(view == null){ 
       view = inflater.inflate(R.layout.first_fragment, null); 
       mViewPager = (ViewPager) view.findViewById(R.id.view_pager); 
       ViewPagerAdapter adapter = new ViewPagerAdapter(mainActivity.getSupportFragmentManager()); 
       mViewPager.setAdapter(adapter); 
     } 
     return view; 
    } 

由於Divyesh評論有好的建議也有需要添加的mainActivity.getSupportFragmentManager()

Answer 2

使用ViewPagerAdapter adapter = new ViewPagerAdapter(getChildFragmentManager());而是試圖驗證碼希望它有幫助

 final ViewPager viewPager = (ViewPager) findViewById(R.id.container); 
    final PagerAdapter adapter = new PaginationAdapter(getSupportFragmentManager(),tabLayout.getTabCount()); 

    viewPager.setAdapter(adapter); 
    viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout)); 
    viewPager.setOffscreenPageLimit(3); 

    tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() { 
     @Override 
     public void onTabSelected(TabLayout.Tab tab) { 

      viewPager.setCurrentItem(tab.getPosition()); 
     } 

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

     } 

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

     } 
    }); 

Answer 3

mViewPager.setOffscreenPageLimit(3);