Memory leakage caused by Handler

First look at a set of simple code

 
 

  
  
public class SampleActivity extends Activity { 
  
  
 
  
  
  private final Handler mHandler = new Handler() { 
  
  
    @Override 
  
  
    public void handleMessage(Message msg) { 
  
  
      // ...  
  
  
    } 
  
  
  } 
  
  
} 
  
  
  
 
 

When we writeActivityMedium,Android LintWill prompt us suchWarning: In Android, Handler classes should be static or leaks might occur..
Meaning:In Android, the Handler class should be static; otherwise, leakage may occur.

Why?

Learn moreHandler

What causes memory leakage? Let's look at the following code.

 
 

  
  
Public class SampleActivity extends Activity {
  
  
 
  
  
Private final Handler mHandler = new Handler (){
  
  
@ Override
  
  
Public void handleMessage (Message msg ){
  
  
//...
  
  
}
  
  
}
  
  
 
  
  
@ Override
  
  
Protected void onCreate (Bundle savedInstanceState ){
  
  
Super. onCreate (savedInstanceState );
  
  
 
  
  
// Send a message that is executed 10 minutes later
  
  
MHandler. postDelayed (new Runnable (){
  
  
@ Override
  
  
Public void run (){}
  
  
},600000 );
  
  
 
  
  
// End the current Activity
  
  
Finish ();
  
  
}
  
  
}
  
  

 
 

WhenActivityAfterMessage queueProcess thisMessagePreviously, it will survive. ThisMessageHoldHandlerAndHandlerYesActivity(SampleActivity) reference, thisActivityAll resources cannot be recycled before message processing, So memory leakage occurs.

The solution is as follows:

 
 

  
  
Public class SampleActivity extends Activity {
  
  
 
  
  
/**
  
  
* Using static internal classes does not hold the reference of the current object
  
  
*/
  
  
Private static class MyHandler extends Handler {
  
  
Private final WeakReference <SampleActivity> mActivity;
  
  
 
  
  
Public MyHandler (SampleActivity activity ){
  
  
MActivity = new WeakReference <SampleActivity> (activity );
  
  
}
  
  
 
  
  
@ Override
  
  
Public void handleMessage (Message msg ){
  
  
SampleActivity activity = mActivity. get ();
  
  
If (activity! = Null ){
  
  
//...
  
  
}
  
  
}
  
  
}
  
  
 
  
  
Private final MyHandler mHandler = new MyHandler (this );
  
  
 
  
  
/**
  
  
* Using static internal classes does not hold the reference of the current object
  
  
*/
  
  
Private static final Runnable sRunnable = new Runnable (){
  
  
@ Override
  
  
Public void run (){}
  
  
};
  
  
 
  
  
@ Override
  
  
Protected void onCreate (Bundle savedInstanceState ){
  
  
Super. onCreate (savedInstanceState );
  
  
 
  
  
// Send a message that is executed 10 minutes later
  
  
MHandler. postDelayed (sRunnable, 600000 );
  
  
 
  
  
// End
  
  
Finish ();
  
  
}
  
  
}
  
  

 
 

OK, end

NOTE:Many people worry about weak references.ActivityWe don't have to worry about recycling, because in this interfaceActivityIt won't be recycled. Think about it.If our Activity is recycled, how does this interface exist?

NOTE2:Ladies and gentlemen, referAsyncTask. Check the document and your own understanding. I still hope you will forgive me for any errors.

NOTE3:I am not clear about how to prevent leaks,HandlerBelow is a piece of source code

 
 

  
  
final Class<? extends Handler> klass = getClass(); 
  
  
            if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) && 
  
  
                    (klass.getModifiers() & Modifier.STATIC) == 0) { 
  
  
                Log.w(TAG, "The following Handler class should be static or leaks might occur: " + 
  
  
                    klass.getCanonicalName()); 
  
  
            }