I am getting a warning in my code that states:
This AsyncTask class should be static or leaks might occur (anonymous android.os.AsyncTask)
The complete warning is:
This AsyncTask class should be static or leaks might occur (anonymous android.os.AsyncTask) A static field will leak contexts. Non-static inner classes have an implicit reference to their outer class. If that outer class is for example a Fragment or Activity, then this reference means that the long-running handler/loader/task will hold a reference to the activity which prevents it from getting garbage collected. Similarly, direct field references to activities and fragments from these longer running instances can cause leaks. ViewModel classes should never point to Views or non-application Contexts.
This is my code:
new AsyncTask<Void,Void,Void>(){
@Override
protected Void doInBackground(Void... params) {
runOnUiThread(new Runnable() {
@Override
public void run() {
mAdapter.notifyDataSetChanged();
}
});
return null;
}
}.execute();
How do I correct this?
To prevent leaks, you can make the inner class static. The problem with that, though, is that you no longer have access to the Activity's UI views or member variables. You can pass in a reference to the Context
but then you run the same risk of a memory leak. (Android can't garbage collect the Activity after it closes if the AsyncTask class has a strong reference to it.) The solution is to make a weak reference to the Activity (or whatever Context
you need).
public class MyActivity extends AppCompatActivity {
int mSomeMemberVariable = 123;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// start the AsyncTask, passing the Activity context
// in to a custom constructor
new MyTask(this).execute();
}
private static class MyTask extends AsyncTask<Void, Void, String> {
private WeakReference<MyActivity> activityReference;
// only retain a weak reference to the activity
MyTask(MyActivity context) {
activityReference = new WeakReference<>(context);
}
@Override
protected String doInBackground(Void... params) {
// do some long running task...
return "task finished";
}
@Override
protected void onPostExecute(String result) {
// get a reference to the activity if it is still there
MyActivity activity = activityReference.get();
if (activity == null || activity.isFinishing()) return;
// modify the activity's UI
TextView textView = activity.findViewById(R.id.textview);
textView.setText(result);
// access Activity member variables
activity.mSomeMemberVariable = 321;
}
}
}
AsyncTask
tutorials out there still don't deal with it (see here, here, here, and here).AsyncTask
were a top-level class. A static inner class is basically the same as a top-level class in Java.If you don't need the Activity itself but still want the Context (for example, to display a Toast
), you can pass in a reference to the app context. In this case the AsyncTask
constructor would look like this:
private WeakReference<Application> appReference;
MyTask(Application context) {
appReference = new WeakReference<>(context);
}
In Kotlin just don't include the inner
keyword for the inner class. This makes it static by default.
class MyActivity : AppCompatActivity() {
internal var mSomeMemberVariable = 123
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// start the AsyncTask, passing the Activity context
// in to a custom constructor
MyTask(this).execute()
}
private class MyTask
internal constructor(context: MyActivity) : AsyncTask<Void, Void, String>() {
private val activityReference: WeakReference<MyActivity> = WeakReference(context)
override fun doInBackground(vararg params: Void): String {
// do some long running task...
return "task finished"
}
override fun onPostExecute(result: String) {
// get a reference to the activity if it is still there
val activity = activityReference.get()
if (activity == null || activity.isFinishing) return
// modify the activity's UI
val textView = activity.findViewById(R.id.textview)
textView.setText(result)
// access Activity member variables
activity.mSomeMemberVariable = 321
}
}
}