I use appcompat library 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 use an AsyncTask and do the network operation in
doInBackGround().
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 code snippets of FragmentA,
MyDialogFragment and AsyncTask :
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
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, fragment A triggers AsyncTask and AsyncTask call methods of
FragmentA to show/dismiss dialog. Fragment A use MyDialogFragment to show
the progress dialog.
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 when dismissing 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
com.example.FragmentA.dismissProgressDialog(FragmentA.java:105)
E/AndroidRuntime(27493): at
com.example.FragmentA.access$1(FragmentA.java:103)
E/AndroidRuntime(27493): at
com.example.FragmentA$GetTokenAsyncTask.onPostExecute(FragmentA.java:40)
E/AndroidRuntime(27493): at
com.example.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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