The issue of calling getactivity Null in Android fragment

When you use fragment, you often encounter a getactivity () null condition. For example, if I call Getactivity () in a callback for an asynchronous network request, a null pointer problem occurs. Solving this problem before is usually avoided by directly adding null pointers, but this does not really solve the problem.

Many people have been plagued by this problem, if the app is running in the background for a long time, it may appear crash when you enter the app again, and there will be overlapping fragment. If the system is out of memory, switching between screens, and the app is running in the background for a long time, theactivity may be reclaimed and rebuilt by the system, but fragment will not be recycled as the activity is recycled. All fragment created will be saved to the bundle, causing fragment to lose the corresponding activity.

Below are some of the source code of Fragmentactivity

    protected void onsaveinstancestate (Bundle outstate) {        super.onsaveinstancestate (outstate);         = mfragments.saveallstate ();         if NULL {            "android:support:fragments", p);}    }

If you click on our app from the most recently used app, the system will restore the activity that was previously recycled, and this time fragmentactivity will do fragment recovery in OnCreate.

@Overrideprotected voidonCreate (Bundle savedinstancestate) {mfragments.attachactivity ( This, Mcontainer,NULL); //Old versions of the platform didn ' t do this!        if(Getlayoutinflater (). GetFactory () = =NULL) {Getlayoutinflater (). Setfactory ( This);              } super.oncreate (Savedinstancestate); Nonconfigurationinstances NC=(nonconfigurationinstances) getlastnonconfigurationinstance (); if(NC! =NULL) {mallloadermanagers=nc.loaders; }        if(Savedinstancestate! =NULL) {parcelable P=savedinstancestate.getparcelable (Fragments_tag); Mfragments.restoreallstate (P, NC!=NULL? Nc.fragments:NULL);    } mfragments.dispatchcreate (); }

Suppose our page is called MyActivity (inherited from Fragmentactivity), where the fragment used is called Myfragment.

When this happens, the app changes as follows:

1, in the earlier mentioned cases, the system recovered the MyActivity

2. Save Myfragment Status by Onsaveinstancestate

3. The user clicks into the app again

4, because the myactivity is recycled, the system will restart the myactivity, based on the previously saved myfragment State recovery fragment

5. In myactivity code logic, the new myfragment will be created again

6, the page appears chaotic, covers two layers of fragment. If the restored myfragment uses the Getactivity () method, the null pointer exception is reported

For the above questions, consider these two workarounds:

1, do not save the state of fragment: MyActivity in the Onsaveinstancestate method, will Super.onsaveinstancestate (outstate); Let it no longer save the state of the fragment, to achieve fragment with the myactivity to destroy the purpose.

2. When rebuilding, clear the state of the saved fragment: The fragment state data in the bundle is cleared before resuming fragment. Here's how:

      if NULL )        {            =  "Android:support:fragments";            Savedinstancestate.remove (Fragments_tag);        }

The issue of calling getactivity Null in Android fragment