I use appcompat library and support library v4 to host some fragments for
tabs. In a specific fragment A, I need to do network operation. In order
not to block the UI thread, I execute an AsyncTask in fragment A and do the
network operation in doInBackGround() of the AsyncTask.
To prevent messing around keep AsyncTask to survive rotation in the
fragment, I call setRetainInstance(true) in the fragment A oncreate().
It works fine but I need to prompt user something when the network
operation is in progress. Therefore, I use DialogFragment. In the
DialogFragment onCreateView(), it instantiates a ProgressDialog and returns.
To be concrete, the following is the FragmentA, MyDialogFragment and
AsyncTask code snippets:
public class FragmentA extends Fragment{ //as tab for actionbar (appcompat)
private boolean isNetworkOperationCalled;
private MyDialogFragment myDialogFragment;
...
public void showProgressDialog(){ //for MyAsyncTask#onPreExecute()
myDialogFragment = new MyDialogFragment();
myDialogFragment.show(getFragmentManager(), "mydialog");
}
public void showProgressDialog(){ //for MyAsyncTask#onPostExecute()
myDialogFragment.dismiss();
}
public void onResume() {
if(!isNetworkOperationCalled){
isNetworkOperationCalled=true;
new MyAsyncTask.execute();//do the network operation
}
}
...
}
public class MyDialogFragment extends DialogFragment{ //ProgressDialog for
FragmentA
...
public Dialog onCreateDialog(Bundle savedInstanceState) {
ProgressDialog progressDialog = new
ProgressDialog(getActivity(),ProgressDialog.STYLE_SPINNER);
... //set the dialog attributes
return progressDialog;
}
...
}
public class MyAsyncTask extends AsyncTask<Void,Void,Void>{ //do network
operation for fragment A
private Fragment fragment;
public GetTokenAsyncTask(Fragment fragmentA){
fragment = fragmentA;
}
protected void onPreExecute() {
fragment.showProgressDialog(); //show progess dialog for users
}
protected String doInBackground(Void... arg0) {
...
}
protected void onPostExecute() { //dismiss the dialog
fragment.dismissProgressDialog();
}
}
In a nutshell, fragmentA triggers AsyncTask, AsyncTask calls methods of
fragmentA to show/dismiss progress dialog (dialog fragment).
The code (method) above works if there is no rotataion occurs while
doInBackground() is executing. Nevertheless, if the rotation happens before
onPostExecute() is called,
the rotation is fine and the progress dialog is retained. Sadly, it crashes
when onPostExecute() finally be called to dismiss the dialog.
E/AndroidRuntime(27493): FATAL EXCEPTION: main
E/AndroidRuntime(27493): java.lang.NullPointerException
E/AndroidRuntime(27493): at
android.support.v4.app.DialogFragment.dismissInternal(DialogFragment.java:184)
E/AndroidRuntime(27493): at
android.support.v4.app.DialogFragment.dismiss(DialogFragment.java:155)
E/AndroidRuntime(27493): at
cyl.ccu.cia.FragmentA.dismissProgressDialog(FragmentA.java:205)
E/AndroidRuntime(27493): at
cyl.ccu.cia.FragmentA.access$1(FragmentA.java:203)
E/AndroidRuntime(27493): at
cyl.ccu.cia.FragmentA$GetTokenAsyncTask.onPostExecute(FragmentA.java:295)
E/AndroidRuntime(27493): at
cyl.ccu.cia.FragmentA$GetTokenAsyncTask.onPostExecute(FragmentA.java:1)
E/AndroidRuntime(27493): at android.os.AsyncTask.finish(AsyncTask.java:631)
E/AndroidRuntime(27493): at
android.os.AsyncTask.access$600(AsyncTask.java:177)
E/AndroidRuntime(27493): at
android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
E/AndroidRuntime(27493): at
android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(27493): at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(27493): at
android.app.ActivityThread.main(ActivityThread.java:4875)
E/AndroidRuntime(27493): at java.lang.reflect.Method.invokeNative(Native
Method)
E/AndroidRuntime(27493): at
java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime(27493): at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:804)
E/AndroidRuntime(27493): at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:571)
E/AndroidRuntime(27493): at dalvik.system.NativeStart.main(Native Method)
How can I solve the problem so that the dialog can dismiss correctly after
rotation?
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