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/**
* This Activity displays the screen's UI, creates a TaskFragment
* to manage the task, and receives progress updates and results
* from the TaskFragment when they occur.
*/
public class MainActivity extends Activity implements TaskFragment.TaskCallbacks {
private static final String TAG_TASK_FRAGMENT = "task_fragment";
private TaskFragment mTaskFragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
FragmentManager fm = getFragmentManager();
mTaskFragment = (TaskFragment) fm.findFragmentByTag(TAG_TASK_FRAGMENT);
// If the Fragment is non-null, then it is currently being
// retained across a configuration change.
if (mTaskFragment == null) {
mTaskFragment = new TaskFragment();
fm.beginTransaction().add(mTaskFragment, TAG_TASK_FRAGMENT).commit();
}
// TODO: initialize views, restore saved state, etc.
}
// The four methods below are called by the TaskFragment when new
// progress updates or results are available. The MainActivity
// should respond by updating its UI to indicate the change.
@Override
public void onPreExecute() { ... }
@Override
public void onProgressUpdate(int percent) { ... }
@Override
public void onCancelled() { ... }
@Override
public void onPostExecute() { ... }
}
// fragment
/**
* This Fragment manages a single background task and retains
* itself across configuration changes.
*/
public class TaskFragment extends Fragment {
/**
* Callback interface through which the fragment will report the
* task's progress and results back to the Activity.
*/
interface TaskCallbacks {
void onPreExecute();
void onProgressUpdate(int percent);
void onCancelled();
void onPostExecute();
}
private TaskCallbacks mCallbacks;
private DummyTask mTask;
/**
* Hold a reference to the parent Activity so we can report the
* task's current progress and results. The Android framework
* will pass us a reference to the newly created Activity after
* each configuration change.
*/
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
mCallbacks = (TaskCallbacks) activity;
}
/**
* This method will only be called once when the retained
* Fragment is first created.
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Retain this fragment across configuration changes.
setRetainInstance(true);
// Create and execute the background task.
mTask = new DummyTask();
mTask.execute();
}
/**
* Set the callback to null so we don't accidentally leak the
* Activity instance.
*/
@Override
public void onDetach() {
super.onDetach();
mCallbacks = null;
}
/**
* A dummy task that performs some (dumb) background work and
* proxies progress updates and results back to the Activity.
*
* Note that we need to check if the callbacks are null in each
* method in case they are invoked after the Activity's and
* Fragment's onDestroy() method have been called.
*/
private class DummyTask extends AsyncTask<Void, Integer, Void> {
@Override
protected void onPreExecute() {
if (mCallbacks != null) {
mCallbacks.onPreExecute();
}
}
/**
* Note that we do NOT call the callback object's methods
* directly from the background thread, as this could result
* in a race condition.
*/
@Override
protected Void doInBackground(Void... ignore) {
for (int i = 0; !isCancelled() && i < 100; i++) {
SystemClock.sleep(100);
publishProgress(i);
}
return null;
}
@Override
protected void onProgressUpdate(Integer... percent) {
if (mCallbacks != null) {
mCallbacks.onProgressUpdate(percent[0]);
}
}
@Override
protected void onCancelled() {
if (mCallbacks != null) {
mCallbacks.onCancelled();
}
}
@Override
protected void onPostExecute(Void ignore) {
if (mCallbacks != null) {
mCallbacks.onPostExecute();
}
}
}
}
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