Die folgende Implementierung kann verwendet werden, um das Problem der Durchführung sicherer Statusänderungen während des ActivityLebenszyklus zu lösen , insbesondere um Dialoge anzuzeigen: Wenn der Instanzstatus bereits gespeichert wurde (z. B. aufgrund einer Konfigurationsänderung), werden sie verschoben, bis der wieder aufgenommene Status vorliegt durchgeführt wurde.
public abstract class XAppCompatActivity extends AppCompatActivity {
private String TAG = this.getClass().getSimpleName();
/** The retained fragment for this activity */
private ActivityRetainFragment retainFragment;
/** If true the instance state has been saved and we are going to die... */
private boolean instanceStateSaved;
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
// get hold of retain Fragment we'll be using
retainFragment = ActivityRetainFragment.get(this, "Fragment-" + this.getClass().getName());
}
@Override
protected void onPostResume() {
super.onPostResume();
// reset instance saved state
instanceStateSaved = false;
// execute all the posted tasks
for (ActivityTask task : retainFragment.tasks) task.exec(this);
retainFragment.tasks.clear();
}
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
instanceStateSaved = true;
}
/**
* Checks if the activity state has been already saved.
* After that event we are no longer allowed to commit fragment transactions.
* @return true if the instance state has been saved
*/
public boolean isInstanceStateSaved() {
return instanceStateSaved;
}
/**
* Posts a task to be executed when the activity state has not yet been saved
* @param task The task to be executed
* @return true if the task executed immediately, false if it has been queued
*/
public final boolean post(ActivityTask task)
{
// execute it immediately if we have not been saved
if (!isInstanceStateSaved()) {
task.exec(this);
return true;
}
// save it for better times
retainFragment.tasks.add(task);
return false;
}
/** Fragment used to retain activity data among re-instantiations */
public static class ActivityRetainFragment extends Fragment {
/**
* Returns the single instance of this fragment, creating it if necessary
* @param activity The Activity performing the request
* @param name The name to be given to the Fragment
* @return The Fragment
*/
public static ActivityRetainFragment get(XAppCompatActivity activity, String name) {
// find the retained fragment on activity restarts
FragmentManager fm = activity.getSupportFragmentManager();
ActivityRetainFragment fragment = (ActivityRetainFragment) fm.findFragmentByTag(name);
// create the fragment and data the first time
if (fragment == null) {
// add the fragment
fragment = new ActivityRetainFragment();
fm.beginTransaction().add(fragment, name).commit();
}
return fragment;
}
/** The queued tasks */
private LinkedList<ActivityTask> tasks = new LinkedList<>();
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
// retain this fragment
setRetainInstance(true);
}
}
/** A task which needs to be performed by the activity when it is "fully operational" */
public interface ActivityTask {
/**
* Executed this task on the specified activity
* @param activity The activity
*/
void exec(XAppCompatActivity activity);
}
}
Dann benutze eine Klasse wie diese:
/** AppCompatDialogFragment implementing additional compatibility checks */
public abstract class XAppCompatDialogFragment extends AppCompatDialogFragment {
/**
* Shows this dialog as soon as possible
* @param activity The activity to which this dialog belongs to
* @param tag The dialog fragment tag
* @return true if the dialog has been shown immediately, false if the activity state has been saved
* and it is not possible to show it immediately
*/
public boolean showRequest(XAppCompatActivity activity, final String tag) {
return showRequest(activity, tag, null);
}
/**
* Shows this dialog as soon as possible
* @param activity The activity to which this dialog belongs to
* @param tag The dialog fragment tag
* @param args The dialog arguments
* @return true if the dialog has been shown immediately, false if the activity state has been saved
* and it is not possible to show it immediately
*/
public boolean showRequest(XAppCompatActivity activity, final String tag, final Bundle args)
{
return activity.post(new XAppCompatActivity.ActivityTask() {
@Override
public void exec(XAppCompatActivity activity) {
if (args!= null) setArguments(args);
show(activity.getSupportFragmentManager(), tag);
}
});
}
/**
* Dismiss this dialog as soon as possible
* @return true if the dialog has been dismissed immediately, false if the activity state has been saved
* and it is not possible to dismissed it immediately
*/
public boolean dismissRequest()
{
return dismissRequest(null);
}
/**
* Dismiss this dialog as soon as possible
* @param runnable Actions to be performed before dialog dismissal
* @return true if the dialog has been dismissed immediately, false if the activity state has been saved
* and it is not possible to dismissed it immediately
*/
public boolean dismissRequest(final Runnable runnable)
{
// workaround as in rare cases the activity could be null
XAppCompatActivity activity = (XAppCompatActivity)getActivity();
if (activity == null) return false;
// post the dialog dismissal
return activity.post(new XAppCompatActivity.ActivityTask() {
@Override
public void exec(XAppCompatActivity activity) {
if (runnable != null) runnable.run();
dismiss();
}
});
}
}
Sie können Dialoge sicher anzeigen, ohne sich über den App-Status Gedanken machen zu müssen:
public class TestDialog extends XAppCompatDialogFragment {
private final static String TEST_DIALOG = "TEST_DIALOG";
public static void show(XAppCompatActivity activity) {
new TestDialog().showRequest(activity, TEST_DIALOG);
}
public TestDialog() {}
@NonNull
@Override
public Dialog onCreateDialog(Bundle savedInstanceState)
{
return new AlertDialog.Builder(getActivity(), R.style.DialogFragmentTheme /* or null as you prefer */)
.setTitle(R.string.title)
// set all the other parameters you need, e.g. Message, Icon, etc.
).create();
}
}
und rufen TestDialog.show(this)Sie dann aus Ihrem XAppCompatActivity.
Wenn Sie eine allgemeinere Dialogklasse mit Parametern erstellen möchten, können Sie diese in a Bundlemit den Argumenten in der show()Methode speichern und mit getArguments()in abrufen onCreateDialog().
Der gesamte Ansatz mag etwas komplex erscheinen, aber sobald Sie die beiden Basisklassen für Aktivitäten und Dialoge erstellt haben, ist er recht einfach zu verwenden und funktioniert einwandfrei. Es kann für andere Fragmentbasierte Vorgänge verwendet werden, die von demselben Problem betroffen sein können.
