FragmentStatePagerAdapterのフラグメントのLifeCycleが予期しないです

Question

ViewPagerを使用してビデオリストを作成したいと思います。私はポケットベル項目がいつ見え、目に見えないのかを知る必要があります。 私はViewPagerのためにFragmentStatePagerAdapterを拡張するVideoListAdapterを使用します。 ビデオの開始または一時停止をトリガーするには、フラグメントメソッドsetUserVisibleHintを使用します。 しかし、問題があります.ViewPagerの位置0にあるフラグメントは、NullPointerExceptionをスローします。そして、私はFragmentのreleatedメソッドのログを出力します。私はVideoListActivityに入って来る
ログ： 07-08 17:06:50.264 E/lemon: startUpdate 07-08 17:06:50.264 E/lemon: instantiateItem 0 07-08 17:06:50.264 E/lemon: getItem 0 07-08 17:06:50.264 E/lemon: setUserVisibleHint 0 isVisibleToUser false 07-08 17:06:50.264 E/lemon: instantiateItem 1 07-08 17:06:50.264 E/lemon: getItem 1 07-08 17:06:50.264 E/lemon: setUserVisibleHint 0 isVisibleToUser false 07-08 17:06:50.264 E/lemon: setPrimaryItem 0 07-08 17:06:50.264 E/lemon: setUserVisibleHint 0 isVisibleToUser true 07-08 17:06:50.264 E/lemon: finishUpdate 07-08 17:06:50.265 E/lemon: onAttach 0 07-08 17:06:50.265 E/lemon: onAttach 1 07-08 17:06:50.265 E/lemon: onCreateView 0 07-08 17:06:50.267 E/lemon: onstart 0 07-08 17:06:50.267 E/lemon: onCreateView 1 07-08 17:06:50.269 E/lemon: onstart 1 07-08 17:06:50.270 E/lemon: startUpdate 07-08 17:06:50.270 E/lemon: setPrimaryItem 0 07-08 17:06:50.270 E/lemon: finishUpdate 07-08 17:06:50.297 E/lemon: startUpdate 07-08 17:06:50.297 E/lemon: setPrimaryItem 0 07-08 17:06:50.297 E/lemon: finishUpdate 07-08 17:06:50.297 E/lemon: startUpdate 07-08 17:06:50.297 E/lemon: setPrimaryItem 0 07-08 17:06:50.297 E/lemon: finishUpdate 07-08 17:06:50.703 E/lemon: startUpdate 07-08 17:06:50.703 E/lemon: setPrimaryItem 0 07-08 17:06:50.703 E/lemon: finishUpdate 07-08 17:06:50.704 E/lemon: startUpdate 07-08 17:06:50.704 E/lemon: setPrimaryItem 0 07-08 17:06:50.704 E/lemon: finishUpdate

私は位置1にスクロールログ： 07-08 17:09:41.154 E/lemon: startUpdate 07-08 17:09:41.154 E/lemon: setPrimaryItem 0 07-08 17:09:41.154 E/lemon: finishUpdate 07-08 17:09:41.966 E/lemon: startUpdate 07-08 17:09:41.966 E/lemon: instantiateItem 2 07-08 17:09:41.967 E/lemon: getItem 2 07-08 17:09:41.967 E/lemon: setUserVisibleHint 0 isVisibleToUser false 07-08 17:09:41.967 E/lemon: setPrimaryItem 1 07-08 17:09:41.967 E/lemon: setUserVisibleHint 0 isVisibleToUser false 07-08 17:09:41.967 E/lemon: setUserVisibleHint 1 isVisibleToUser true 07-08 17:09:41.967 E/lemon: finishUpdate 07-08 17:09:41.968 E/lemon: onAttach 2 07-08 17:09:41.968 E/lemon: onCreateView 2 07-08 17:09:41.971 E/lemon: onstart 2 07-08 17:09:41.971 E/lemon: startUpdate 07-08 17:09:41.971 E/lemon: setPrimaryItem 1 07-08 17:09:41.971 E/lemon: finishUpdate 07-08 17:09:41.972 E/lemon: startUpdate 07-08 17:09:41.972 E/lemon: setPrimaryItem 1 07-08 17:09:41.972 E/lemon: finishUpdate
私はこれらのログを分析し、私はpositino 0でフラグメントがsetUserVisibleHint（true）を呼び出すことがわかり最初にしONATTACHを（呼び出します）、位置1のフラグメントは最初にonAttach（）を呼び出し、その後にsetUserVisibleHint（true）を呼び出します。

私は、onAttach（）とsetUserVisibleHint（true）の両方で呼び出されたFragmentのメソッドをonTrigger（）に書き込みますが失敗します。私は私のコードをデバッグし、onTrigger（）のisAdded（）はonAttach（）のonTriggerを呼び出すときにfalseを返します。

ビデオの開始をいつ開始するかを教えてください。どうもありがとう。

public class FullScreenVideoFragment extends Fragment { 

    private FragmentFullScreenVideoBinding binding; 
    int colorRes; 
    int position; 

    @Nullable 
    @Override 
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 
     Log.e("lemon", "onCreateView " + position); 
     binding = DataBindingUtil.inflate(inflater, R.layout.fragment_full_screen_video, container, false); 
     setView(); 
     return binding.getRoot(); 
    } 

    @Override 
    public void onCreate(@Nullable Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
    } 

    public void setBgAndPosition(int position, int colorRes) { 
     this.position = position; 
     this.colorRes = colorRes; 
    } 

    @Override 
    public void onAttach(Context context) { 
     Log.e("lemon", "onAttach " + position); 
     super.onAttach(context); 
     onTriger(); 
    } 

    @Override 
    public void onDetach() { 
     Log.e("lemon", "onDetach " + position); 
     super.onDetach(); 
    } 

    @Override 
    public void onAttachFragment(Fragment childFragment) { 
     Log.e("lemon", "onAttachFragment " + position); 
     super.onAttachFragment(childFragment); 
    } 

    @Override 
    public void setUserVisibleHint(boolean isVisibleToUser) { 
     Log.e("lemon", "setUserVisibleHint " + position + " isVisibleToUser " + isVisibleToUser); 
     super.setUserVisibleHint(isVisibleToUser); 
     onTriger(); 
    } 

    private void setView() { 
     binding.getRoot().setBackgroundResource(colorRes); 
     binding.position.setText(String.valueOf(position)); 
    } 

    private void onTriger() { 
     if (!isVisible()) return; 
     binding.position.setText(position + " start"); 
    } 
} 

public class VideoListAdapter extends FragmentStatePagerAdapter { 
    private LinkedList<FullScreenVideoFragment> fragmentCaches; 
    private int[] colors = new int[]{android.graphics.Color.RED, android.graphics.Color.BLUE, android.graphics.Color.GREEN}; 

    public VideoListAdapter(FragmentManager fm) { 
     super(fm); 
     fragmentCaches = new LinkedList<>(); 
    } 

    @Override 
    public Fragment getItem(int position) { 
     Log.e("lemon", "getItem " + position); 
     FullScreenVideoFragment fragment = generateItem(); 
     return fragment; 
    } 

    @Override 
    public int getCount() { 
     return 10; 
    } 

    @Override 
    public void destroyItem(ViewGroup container, int position, Object object) { 
     Log.e("lemon", "destroyItem " + position); 
     super.destroyItem(container, position, object); 
    } 

    @Override 
    public void setPrimaryItem(ViewGroup container, int position, Object object) { 
     Log.e("lemon", "setPrimaryItem " + position); 
     super.setPrimaryItem(container, position, object); 
    } 

    @Override 
    public Object instantiateItem(ViewGroup container, int position) { 
     Log.e("lemon", "instantiateItem " + position); 
     FullScreenVideoFragment fragment = (FullScreenVideoFragment) super.instantiateItem(container, position); 
     fragment.setBgAndPosition(position, colors[position % 3]); 
     return fragment; 
    } 

    @Override 
    public void startUpdate(ViewGroup container) { 
     Log.e("lemon", "startUpdate"); 
     super.startUpdate(container); 
    } 

    @Override 
    public void finishUpdate(ViewGroup container) { 
     Log.e("lemon", "finishUpdate"); 
     super.finishUpdate(container); 
    } 

    @Override 
    public void restoreState(Parcelable state, ClassLoader loader) { 
     Log.e("lemon", "restoreState"); 
     super.restoreState(state, loader); 
    } 

    @Override 
    public Parcelable saveState() { 
     Log.e("lemon", "saveState"); 
     return super.saveState(); 
    } 

    private FullScreenVideoFragment generateItem() { 
     FullScreenVideoFragment neededFragment = null; 
     if (!fragmentCaches.isEmpty()) { 
      neededFragment = fragmentCaches.get(0); 
      fragmentCaches.remove(0); 
      return neededFragment; 
     } 
     neededFragment = new FullScreenVideoFragment(); 
     return neededFragment; 
    } 
} 

フラグメントのxml：私はフラグメントが頻繁に切り替えるには、これらの三つの方法を使用することがわかった

<?xml version="1.0" encoding="utf-8"?> 
<layout xmlns:android="http://schemas.android.com/apk/res/android"> 

    <data></data> 

    <RelativeLayout 
     android:layout_width="match_parent" 
     android:layout_height="match_parent"> 
     <TextView 
      android:id="@+id/position" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_centerInParent="true" 
      android:textColor="@color/account_name_color"/> 
    </RelativeLayout> 
</layout> 

Answer 1

：

• ショーは/

• を置き換える（/デタッチを添付隠します）

• ViewPager

これらの3つの方法がいくつかの違いがあります目に見える状態を断片化につながるので、私は、これらの3つの方法を区別するために、次のクラスを定義しました。フラグメントのグループが同じ方法でスイッチを使用している場合は、異なる方法でスイッチを切り替えると信頼できるはずです。それからわか​​りませんが、注意深いテストはありません。

import android.support.annotation.IntDef; 
import android.support.v4.app.Fragment; 

import java.lang.annotation.Retention; 
import java.lang.annotation.RetentionPolicy; 

/** 
* Created by Kilnn on 2017/7/12. 
* A smart fragment know itself's visible state. 
*/ 
public abstract class SmartFragment extends Fragment { 

    private boolean isFragmentVisible; 

    @Override 
    public void onResume() { 
     super.onResume(); 
     int switchType = getSwitchType(); 
     if (switchType == ATTACH_DETACH) { 
      notifyOnFragmentVisible(); 
     } else if (switchType == SHOW_HIDE) { 
      if (!isHidden()) { 
       notifyOnFragmentVisible(); 
      } 
     } else if (switchType == VIEW_PAGER) { 
      //If the parent fragment exist and hidden when activity destroy, 
      //when the activity restore, The parent Fragment will be restore to hidden state. 
      //And the sub Fragment which in ViewPager is also be restored, and the onResumed() method will callback. 
      //And The sub Fragment's getUserVisibleHint() method will return true if it is in active position. 
      //So we need to judge the parent Fragment visible state. 
      if (getUserVisibleHint() && isParentFragmentVisible()) { 
       notifyOnFragmentVisible(); 
      } 
     } 
    } 

    @Override 
    public void setUserVisibleHint(boolean isVisibleToUser) { 
     super.setUserVisibleHint(isVisibleToUser); 
     int switchType = getSwitchType(); 
     if (switchType == VIEW_PAGER) { 
      if (isVisibleToUser) { 
       notifyOnFragmentVisible(); 
      } else { 
       notifyOnFragmentInvisible(); 
      } 
     } 
    } 

    @Override 
    public void onHiddenChanged(boolean hidden) { 
     super.onHiddenChanged(hidden); 
     int switchType = getSwitchType(); 
     if (switchType == SHOW_HIDE) { 
      if (hidden) { 
       notifyOnFragmentInvisible(); 
      } else { 
       notifyOnFragmentVisible(); 
      } 
     } 
    } 

    @Override 
    public void onPause() { 
     super.onPause(); 
     notifyOnFragmentInvisible(); 
    } 

    private boolean isParentFragmentVisible() { 
     Fragment parent = getParentFragment(); 
     if (parent == null) return true; 
     if (parent instanceof SmartFragment) { 
      return ((SmartFragment) parent).isFragmentVisible(); 
     } else { 
      //TODO May be can't get the correct visible state if parent Fragment is not SmartFragment 
      return parent.isVisible(); 
     } 
    } 

    public boolean isFragmentVisible() { 
     // Don't judge the state of the parent fragment, 
     // because if the parent fragment visible state changes, 
     // you must take the initiative to change the state of the sub fragment 
//  return isFragmentVisible && isParentFragmentVisible(); 
     return isFragmentVisible; 
    } 

    public void notifyOnFragmentVisible() { 
     if (!isFragmentVisible) { 
      onFragmentVisible(); 
      isFragmentVisible = true; 
     } 
    } 

    public void notifyOnFragmentInvisible() { 
     if (isFragmentVisible) { 
      onFragmentInvisible(); 
      isFragmentVisible = false; 
     } 
    } 

    /** 
    * If this method callback, the Fragment must be resumed. 
    */ 
    public void onFragmentVisible() { 

    } 

    /** 
    * If this method callback, the Fragment maybe is resumed or in onPause(). 
    */ 
    public void onFragmentInvisible() { 

    } 

    /** 
    * Fragments switch with attach/detach(replace) 
    */ 
    public static final int ATTACH_DETACH = 0; 

    /** 
    * Fragments switch with show/hide 
    */ 
    public static final int SHOW_HIDE = 1; 

    /** 
    * Fragments manage by view pager 
    */ 
    public static final int VIEW_PAGER = 2; 

    @Retention(RetentionPolicy.SOURCE) 
    @IntDef({ATTACH_DETACH, SHOW_HIDE, VIEW_PAGER}) 
    @interface SwitchType { 
    } 

    @SwitchType 
    public abstract int getSwitchType(); 

} 

したがって、onFragmentVisible（）でTrigger（）を使用できます。