Develop Reference

Get state of activity (paused / resumed)

I am using a LoaderManager to get some data and when it finishes a child fragment should be shown. In some cases this happens when the activity is already in paused state and can not perform the fragment transaction.
Is there a way to get the current state of the activity (seems to have a mResume flag)? Or do I have to maintain my own boolean?

The new Architecture Components allow you to do it with:
this.getLifecycle().getCurrentState()

A quick look in the Activity source code indicates that the Activity class does keep track on the resume state with the member mResumed. But since mResume is not public and isResumed() is hidden, we can't use them.
You can have a simple solution to provide you with that information for all your classes. Simply create a base Activity class that store the state. For example:
public class ActivityBase extends Activity {
private boolean mIsResumed = false;
#Override
public void onResume() {
super.onResume()
mIsResumed = true;
}
#Override
public void onPaused() {
super.onPaused()
mIsResumed = false;
}
public boolean isResumed() {
return mIsResumed
}
}
Simply extend this class with your class:
public class MyActivity extends ActivityBase {
private void onLoadDone() {
if (isResumed()) {
// Show the fragment
}
}
}

One way it could be achieved is by using breakpoints on your Activity (for instance, putting a breakpoint in your onResume method), and using the Evaluate Expression window that you can open by clicking a right click on your Debug menu window, and selecting it from there (OR SHIFT + F8) for mac. Once opened, you can intercept the current state (depending where your breakpoint is) using this line in your Evaluate Expression Window:
getLifecycle().getCurrentState().isAtLeast(Lifecycle.State.RESUMED)
If it returns true, that means your Activity is currently in the resume state.
If false, it's in another state.
They have plenty of other states you can play with, just check here

Android: Is There A Way To Wait Until A Fragment Attaches To An Activity?

So Adopting The Design Pattern described here whereby a Async Task wrapped around a retained fragment via the setRetainInstance as seen described here
http://www.androiddesignpatterns.com/2013/04/retaining-objects-across-config-changes.html
Im having an issue where a task is started before the worker fragment can attach to the activity leaving the mCallBack to be null at the same time onPreExecute is called which throws a nullPointerException/
This is largely due to the fact that the async task is started via a method call (a start method which creates an instance of the inner async task) and not inside onCreate or OnActivityCreated since the task can be started again (under a new instance of it) and cannot be done so in onCreate or OnActivity created since the life cycle of these methods only call 1 time because of the setRetainInstance as far I as know.
My question is where a way to program some sort of routine whereby a wait until fragment has attached to activity routine and if so do the task that you need to do?
Many thanks.
Update1: Code Posted
This is how the worker fragment is being added. When the user presses the send feedback button. This OnClick Listener is invoked. The final if statement you see is what starts the async task. Note that this code is inside another fragment.
#Override
public void onClick(View v)
{
// TODO Auto-generated method stub
FragmentManager fm = getActivity().getSupportFragmentManager();
mThreadFragment = (ConnectToServerForResults) fm.findFragmentByTag(ConnectToServerForResults.class.getName());
if(mThreadFragment == null)
{
mThreadFragment = new ConnectToServerForResults();
fm.beginTransaction().add(mThreadFragment, ConnectToServerForResults.class.getName()).commit();
}
if(!mThreadFragment.isRunning())
{
mThreadFragment.startSendFeedBack(3, preventSQLInjections(),getResources().getString(R.string.app_name));
}
else
{
//Work in progress :D
}
}
Worker Fragment Start Task Method
public void startSendFeedBack(int requestCode,String feedback,String appName)
{
XAMPP_URL ="http://10.0.2.2/testStuff/feed.php";
http = new HTTPConnection();
http.execute(String.valueOf(requestCode),XAMPP_URL,feedback,appName);
mRunning = true;
}
Worker Fragment OnAttach
#Override
public void onAttach(Activity activity)
{
// TODO Auto-generated method stub
super.onAttach(activity);
Log.d("ERSEN", "onAttach");
if(!(activity instanceof ResultAsyncTaskCallbacks))
{
throw new IllegalStateException("activity must implement the AsyncTaskCallbacks interface.");
}
mCallback = (ResultAsyncTaskCallbacks) activity;
}

so I made a solution which solved the problems. May not be the best solution but my problems appear resolved.
I added a call back to my interface called onThreadFragmentAttached()
public static interface ResultAsyncTaskCallbacks
{
void onPreExecuteResults();
void onCancelledResults();
void onPostExecuteResults();
void onThreadFragmentAttached();
}
I added a class variable to the worker fragment
private boolean isFirstTime=true;
This Boolean at the start says that the fragment is being added for the first time
In OnActivityCreated I can safely assume that the fragment is attached because this is what that method signifies.
In there is this logic. Check if firstTime is true (yes would be if the fragment is added for the first time). If call onThreadFragmentAttached();. Set firstTime to false because the fragment is added. This false is preserved through config changes because this fragment is retained.
if(isFirstTime == true)
{
mCallback.onThreadFragmentAttached();
isFirstTime = false;
}
In main activity which implements the callbacks
#Override
public void onThreadFragmentAttached(int fragmentCode)
{
FB = (FeedBack)fragmentManger.findFragmentByTag(FeedBack.class.getName());
FB.sendFeedback();
}
Find the feedback fragment (this was my fragment which needed to start a task) and call sendFeedBack method.
This is the method which simply calls the start method.
public void sendFeedback()
{
mThreadFragment.startSendFeedBack(3, preventSQLInjections(),getResources().getString(R.string.app_name));
}
In my onClick I have the following logic
//Check if there is not a task running at the moment
if(!mThreadFragment.isRunning()) //No task
{
//if its the first time worker fragment is being added it will start the task itself via the onThreadFragmentAttached callback (inside main activity) which then calls the sendFeedBack method that starts the task
if(mThreadFragment.getIsFirstTime() != true) //this is here in cases where the thread fragment is already attached and the task can be started as normal.
{
sendFeedback();
}
}
This checks if the fragment has already been added and just to go ahead and start the task. Note the getIsFirstTime method just returns the value of the class variable isFirstTime. If its false proceed as normal because its already attached. if it was true this would be bypassed and the task would start anyway via the onThreadAttachedCallback();

ProgressDialog, activity's onCreate() and AsyncTask

This question has to do with an AsyncTask that needs to kill a ProgressDialog. While the task is running, the activity gets destroyed and recreated (phone rotation, for example). A new dialog gets made with the help of onSaveInstanceState() but the AsyncTask, spawned by the previously destroyed activity, can't see it.
Picture, if you will... (quick mockup code for example's sake).
public class Bob extends Activity {
private ProgressDialog m_d;
public void onCreate(Bundle b) {
m_d = new ProgressDialog(this);
// ...
if (b != null) {
if (b.getBoolean("dialog") == true)
m_d.show();
}
// ...
}
public void onSaveInstanceState(Bundle b) {
super.onSaveInstanceState(b);
b.putBoolean("dialog", (m_d.isShowing()));
}
public void onDestroy() {
if (m_d.isShowing()) {
m_d.dismiss();
m_d = null;
}
//...
}
}
The AsyncTask onPreExecute() does m_d.show() and onPostExecute() does m_d.hide().
The problem is when my activity gets recreated (say, on phone rotation), the AsyncTask seems to have the old m_d. It is null, because that got killed in onDestroy().
It doesn't have the new m_d, created when the activity got recreated. So now I have a ProgressDialog and the guy who was supposed to kill it in onPostExecute() can't see it.
Now what? I need the old AsyncTask to somehow signal the new ProgressDialog to go away.
private OnItemSelectedListener onSpinnerSelection = new OnItemSelectedListener() {
public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
// ...
new Switcharoo().execute();
}
}
private class Switcharoo extends AsyncTask<Void, Void, Void> {
protected void onPreExecute() {
m_d.show();
// ...
}
protected void onPostExecute() {
if (m_d != null) m_d.hide();
// ...
}
protected Void doInBackground(Void... arg0) {
// ...
}
}
If Android doesn't kill my activity while the task is running, it's fine. The ProgressDialog pops up and goes away like I expect.
If Android decides to restart my activity for any reason while the task is running, m_d will be null in onPostExecute() even though I recreated it in onCreate() - it has the old m_d, not the new one.

There are two problems: the first is that the AsyncTask is bound to the activity that has created it. I mean, the instance of the activity.
If you want it to survive between activities rotations you have to store it somewhere else (check this for example). In any case, you need to have a reference to it from the new activity (another thing you could do is to use a model fragment, i.e. a fragment with no UI that you set as setRetainInstance(true)).
Once you have the reference to the async task from the newly created activity, nothing prevents you to have m_d local to the async task and a setter method that updates it with the new dialog.
Note also that it would be a good practice to have weak references pointing to the activity and the dialog itself in order to allow garbage collection. Otherwise the dialog (and probably the activity itself) would not be freed until the execution of the task itself ended.

How to handle AsyncTask onPostExecute when paused to avoid IllegalStateException

I appreciate the numerous postings regarding AsyncTask on a rotation change. I have the following problem when using the compatability lib and trying to dismiss a DialogFragment in onPostExecute.
I have a fragment which fires of an AsyncTask which displays a progress DialogFragment, then in onPostExecute dismisses the dialog and then potentially throws up another DialogFragment.
If when the progress dialog is being displayed I put the application into the background I get the following for my fragment:
1) onPause
2) onSaveInstanceState
3) onPostExecute in which I try to dismiss and invoke a dialog.
I get an IllegalStateException because I'm trying to effectively commit a transaction when the activity has saved its state and I understand this.
On a rotation I've assumed (perhaps incorrectly) that I wouldn't get an onPostExecute until the activity has been recreated. However, when putting the application into the background I assumed (definitely incorrectly) that the onPostExectute wouldn't get called while the fragment/activity was paused.
My question is, is my solution to simply detect in onPostExecute that the fragment/activity is paused and simply perform what I need to do in onResume instead? Seems somewhat ugly to me.
Thanks in advance, peter.
Edit 1
Need to support 2.1 and above
Edit 2
I have considered showing the dialog using FragmentTransaction:add and FragmentTransaction:commitAllowingStateLosshowever this isn't without its problems.

If you need to synchronize your task with the activity lifecycle, I believe that Loaders are exactly what you need. More specifically, you should use AsyncTaskLoader to do the job. So now instead of running an AsyncTask, you launch your loader, then wait for response in a listener. If the activity is paused, you won't get a callback, this part will be managed for you.
There is another way to handle this task: using a fragment which retains its instance. The general idea is that you create a fragment without UI and call setRetainInstance(true). It has a task which is being notified about the activity being available or not. If not, the task's thread suspends until an activity becomes available.

Another way of achieving what you require is to implement the PauseHandler class that I documented in this post.
Then in your onPostExecute method call sendMessage() to post your message into the handler.
When your application resumes the action will be handled.

Rather then using BroadcastReceiver, I prefer using bus libraries like guava, otto or eventbus. Their performance is much better then the broadcast receiver implementation.

I came up with a solution for this problem without any major workaround:
The basic idea how to maintain a progressdialog and a asynctask is described in this blogentry (of course I used the AsyncTaskComplex-Version). All credits go to the author of this blogentry, I only added a tiny thing:
Obviously I'm not using showDialog() anymore. Instead I stick with DialogFragments.
The second tweak is the importent one and also solves the problem with the IllegalStateException:
Instead of only telling the asynctask in onRetainCustomNonConfigurationInstance() that there is no more activity I also do it in onPause(). And instead of only telling the asynctask in onCreate() that there is a new activity I also do it in onResume().
And there you go, your AsyncTask will not try to inform your activity about his finish causing an IllegalStateException when the activity is not visible.
If you would like to see more code instead of words, leave a comment.
/edit:
Sourcecode to show my solution, which I think is a pretty decent one :)
public class MyActivity extends Activity {
private MyTask mTask;
#Override
protected void onCreate(Bundle pSavedInstanceState) {
super.onCreate(pSavedInstanceState);
setContentView(R.layout.editaccount);
Object retained = getLastCustomNonConfigurationInstance();
if ( retained instanceof NewContactFolderIdTask ) {
mTask = (MyTask) retained;
mTask.setActivity(this);
}
}
#Override
protected void onPause() {
if(mTask != null) {
mTask.setActivity(null);
}
super.onPause();
}
#Override
public Object onRetainCustomNonConfigurationInstance() {
if(mTask != null) {
mTask.setActivity(null);
return mTask;
}
return null;
}
#Override
protected void onResume() {
if(mTask != null) {
mTask.setActivity(this);
}
loadValues(); // or refreshListView or whatever you need to do
super.onResume();
}
public void onTaskCompleted() {
loadValues(); // or refreshListView or whatever you need to do
DialogFragment dialogFragment = (DialogFragment) getSupportFragmentManager().findFragmentByTag(PROGRESS_DIALOG_FRAGMENT);
if(dialogFragment != null) {
dialogFragment.dismiss();
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater menuInflater = getMenuInflater();
menuInflater.inflate(R.menu.main, menu);
return super.onCreateOptionsMenu(menu);
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
// app icon in Action Bar clicked; go home
Intent intent = new Intent(this, OXClient.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
return true;
case R.id.menu_refresh:
mTask = new MyTask(this);
mTask.execute();
break;
}
return super.onOptionsItemSelected(item);
}
private class NewContactFolderIdTask extends AsyncTask<Boolean, Integer, Bundle> {
private MyActivity mActivity;
private boolean mCompleted;
private NewContactFolderIdTask(MyActivity pActivity) {
this.mActivity = pActivity;
}
public void setActivity(MyActivity pActivity) {
this.mActivity = pActivity;
if(mCompleted) {
notifiyActivityTaskCompleted();
}
}
private void notifiyActivityTaskCompleted() {
if(mActivity != null) {
mActivity.onTaskCompleted();
}
}
#Override
protected Bundle doInBackground(Boolean... pBoolean) {
// Do your stuff, return result
}
#Override
protected void onPreExecute() {
DialogFragment newFragment = ProgressDialogFragment.newInstance();
newFragment.show(getSupportFragmentManager(), PROGRESS_DIALOG_FRAGMENT);
}
#Override
protected void onPostExecute(Bundle pResult) {
mCompleted = true;
notifiyActivityTaskCompleted();
}
}
}

On How to handle Handler messages when activity/fragment is paused I offer another approach using a BroadcastReceiver.
I consider it cleaner more elegant and it offers the advantages that you can invoke code on your base fragment from everywhere within your app and by using sticky broadcasts your invocation can be "remembered" and executed after your fragment resumes.

How to determine fragment restored from backstack

Been searching for this issue for a while to no avail now:
How to determine fragment is being restored from backstack?
I'm using the compatibility library and a ListFragment inside a FragmentActivity. When an item inside ListFragment is selected, a new Fragment is started to replace the ListFragment.
I noticed that when the FragmentActivity gets paused, the Fragment's onSaveInstanceState is called. But when the Fragment is put into the back stack via FragmentTransaction, onSaveInstanceState doesn't get called, then the lifecycle methods onCreateView and onActivityCreated gets called with null savedInstanceState Bundle.
I'm asking this because I want to load some data when the Fragment is created or restored, but not so when user comes back via. backstack.
I've looked at How to check if Fragment was restored from a backstack?
but want to add more details in hopes this would incite an answer.
Edit:
just noticed http://developer.android.com/reference/android/app/Fragment.html#onSaveInstanceState(android.os.Bundle)
says
Note however: this method may be called at any time before onDestroy(). There are many situations where a fragment may be mostly torn down (such as when placed on the back stack with no UI showing), but its state will not be saved until its owning activity actually needs to save its state.
So onSaveInstanceState is definitely out of the question...

I think that most simple way is do this for example in onViewCreated() method:
if (savedInstanceState == null && !mAlreadyLoaded) {
mAlreadyLoaded = true;
// Do this code only first time, not after rotation or reuse fragment from backstack
}
Because when android put fragment on backstack, it only destroy its view, but don't kill instance itself, so mAlreadyLoaded will be still true when fragment will be restored from backstack.

getSupportFragmentManager().addOnBackStackChangedListener(new OnBackStackChangedListener() {
public void onBackStackChanged() {
Log.i(TAG, "back stack changed ");
int backCount = getSupportFragmentManager().getBackStackEntryCount();
if (backCount == 0){
// block where back has been pressed. since backstack is zero.
}
}
});
use this addOnBackStackChangedListener.

When a fragment goes to back-stack onDestroyView() called. Not onDestroy().
And when a fragment pops from back-stack onCreateView() called. Not onCreate().
So add a boolean mIsRestoredFromBackstack to fragment and follow as below:
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
mIsRestoredFromBackstack = false;
}
#Override
public void onResume()
{
super.onResume();
if(mIsRestoredFromBackstack)
{
// The fragment restored from backstack, do some work here!
}
}
#Override
public void onDestroyView()
{
super.onDestroyView();
mIsRestoredFromBackstack = true;
}

MAJOR EDIT: Oct 15 2013
The previous explanation (kept below for reference) fails when the application is put to the background and brought back to the foreground.
Instead, it is better to compare the current size of the backstack with the one when the fragment was created & put into the backstack.
Take a good look at Figure 2 in http://developer.android.com/guide/components/fragments.html#Creating
What this figure tells you is that when a fragment is restored from the backstack, its onCreate() is not called, while its onCreateView() is.
So, you may want to do something like this:
public class MyFragment extends Fragment {
int mBackStackSize = 0;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mBackStackSize = getFragmentManager().getBackStackEntryCount();
}
public boolean isRestoredFromBackstack() {
return mBackStackSize > getFragmentManager().getBackStackEntryCount();
}
}

If you added fragment to backstack, and after some manipulation you hide it using fragmentTransaction.hide(fragment) and then restore it from backstack like fragmentTransaction.show(fragmentManager.findFragmentByTag(fragment.getName())); you can override onHiddenChanged(boolean hidden)
#Override
public void onHiddenChanged(boolean hidden) {
// TODO Auto-generated method stub
super.onHiddenChanged(hidden);
if (!hidden) {
//fragment became visible
//your code here
}
}

In some cases you can use isVisible method to understand is it first showing of a fragment or is it restored from the backstack.