您無法在未連接的視圖或片段上啓動加載，其中getActivity（）返回空值

Question

我正在使用FragmentStatePagerAdapter在活動中顯示5個片段。在每個活動中，我顯示的是從FirebaseListAdapter/FirebaseRecyclerAdapter。因爲它是FragmentStagePagerAdapter相鄰的視圖/片段將被初始化，即使它們不可見。如果標籤以快速方式滾動（向前/向後），應用程序崩潰與上述錯誤。我發現了一些類似的問題在互聯網上，但沒有能夠解決此問題。我也越來越如果我開始一個新的活動（在活動中，我在網格視圖中顯示來自Firebase的圖像）並立即關閉它（按下按鈕），您無法爲已銷燬的活動啓動加載錯誤後退按鈕） 我正在使用以下代碼。

adapt= new FirebaseListAdapter<MyClassStudent>(getActivity(), MyClassStudent.class, R.layout.mychild_grid_template, myRef) { 
      @Override 
      protected void populateView(final View v, MyClassStudent model, int position) { 
       final TextView uname = (TextView) v.findViewById(R.id.mychild_uname); 

       final CircleImageView profileImage=(CircleImageView)v.findViewById(R.id.mychild_image); 
       studRef.child(model.getUsername()).addListenerForSingleValueEvent(new ValueEventListener() { 
        public void onDataChange(DataSnapshot dataSnapshot) { 
         Child child=dataSnapshot.getValue(Child.class); 
         uname.setText(child.getUsername()); 
         Glide.with(getActivity()).load(child.getProfileImage()).into(profileImage); 
        } 

        @Override 
        public void onCancelled(DatabaseError databaseError) { 

        } 
       }); 
      } 
     }; 

堆棧跟蹤：

E/UncaughtException: java.lang.NullPointerException: You cannot start a load on a not yet attached View or a Fragment where getActivity() returns null (which usually occurs when getActivity() is called before the Fragment is attached or after the Fragment is destroyed). 
         at com.bumptech.glide.util.Preconditions.checkNotNull(Preconditions.java:27) 
         at com.bumptech.glide.Glide.getRetriever(Glide.java:509) 
         at com.bumptech.glide.Glide.with(Glide.java:563) 
         at com.mycompany.educareteacher.FragmentStudents$2$1.onDataChange(FragmentStudents.java:184) 
         at com.google.firebase.database.zzp.onDataChange(Unknown Source) 
         at com.google.android.gms.internal.tl.zza(Unknown Source) 
         at com.google.android.gms.internal.vg.zzHW(Unknown Source) 
         at com.google.android.gms.internal.vm.run(Unknown Source) 
         at android.os.Handler.handleCallback(Handler.java:739) 
         at android.os.Handler.dispatchMessage(Handler.java:95) 
         at android.os.Looper.loop(Looper.java:148) 
         at android.app.ActivityThread.main(ActivityThread.java:5438) 
         at java.lang.reflect.Method.invoke(Native Method) 
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738) 
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628) 
D/FA: Logging event (FE): app_exception(_ae), Bundle[{firebase_event_origin(_o)=crash, firebase_screen_class(_sc)=ClassDetailActivity, firebase_screen_id(_si)=-4663411025690523798, timestamp=1500710706898, fatal=1}] 
V/FA: Recording user engagement, ms: 3544 
D/FA: Logging event (FE): user_engagement(_e), Bundle[{firebase_event_origin(_o)=auto, engagement_time_msec(_et)=3544, firebase_screen_class(_sc)=ClassDetailActivity, firebase_screen_id(_si)=-4663411025690523798}] 
E/AndroidRuntime: FATAL EXCEPTION: main 
        Process: com.mycompany.com.educareteacher, PID: 5154 
        java.lang.NullPointerException: You cannot start a load on a not yet attached View or a Fragment where getActivity() returns null (which usually occurs when getActivity() is called before the Fragment is attached or after the Fragment is destroyed). 
         at com.bumptech.glide.util.Preconditions.checkNotNull(Preconditions.java:27) 
         at com.bumptech.glide.Glide.getRetriever(Glide.java:509) 
         at com.bumptech.glide.Glide.with(Glide.java:563) 
         at com.mycompany.educareteacher.FragmentStudents$2$1.onDataChange(FragmentStudents.java:184) 
         at com.google.firebase.database.zzp.onDataChange(Unknown Source) 
         at com.google.android.gms.internal.tl.zza(Unknown Source) 
         at com.google.android.gms.internal.vg.zzHW(Unknown Source) 
         at com.google.android.gms.internal.vm.run(Unknown Source) 
         at android.os.Handler.handleCallback(Handler.java:739) 
         at android.os.Handler.dispatchMessage(Handler.java:95) 
         at android.os.Looper.loop(Looper.java:148) 
         at android.app.ActivityThread.main(ActivityThread.java:5438) 
         at java.lang.reflect.Method.invoke(Native Method) 
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738) 
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628) 

我怎樣才能解決這個問題？

Answer 1

您的片段響應從火力點來之前分離，所以儘量使用

public void onDataChange(DataSnapshot dataSnapshot) { 
    if (getActivity() == null) { 
     return; 
    } 
    Child child = dataSnapshot.getValue(Child.class); 
    uname.setText(child.getUsername()); 
    Glide.with(getActivity()).load(child.getProfileImage()).into(profileImage); 
} 

你可以這樣做檢查活動爲空或不是在別的地方之前檢查getActivity()空。

private Activity mActivity; 

@Override 
public void onAttach(Context context) { 
    super.onAttach(context); 

    mActivity = getActivity(); 
} 

@Override 
public void onDetach() { 
    super.onDetach(); 
    mActivity = null; 
} 

private void doAction() { 
    if (mActivity == null) { 
     return; 
    } 

    adapt = new FirebaseListAdapter<MyClassStudent>(mActivity, MyClassStudent.class, R.layout.mychild_grid_template, myRef) { 
     @Override 
     protected void populateView(final View v, MyClassStudent model, int position) { 
      final TextView uname = (TextView) v.findViewById(R.id.mychild_uname); 

      final CircleImageView profileImage = (CircleImageView) v.findViewById(R.id.mychild_image); 
      studRef.child(model.getUsername()).addListenerForSingleValueEvent(new ValueEventListener() { 
       public void onDataChange(DataSnapshot dataSnapshot) { 
        if (mActivity == null) { 
         return; 
        } 
        Child child = dataSnapshot.getValue(Child.class); 
        uname.setText(child.getUsername()); 
        Glide.with(mActivity).load(child.getProfileImage()).into(profileImage); 
       } 

       @Override 
       public void onCancelled(DatabaseError databaseError) { 

       } 
      }); 
     } 
    }; 
} 

Answer 2

我更喜歡在使用Glide加載圖像之前使用isAdded()片段的方法。