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Best practices for start() and stop() in Android MVP?

I have some questions regarding the Presenter’s start(), stop() method. What would you normally put into these methods to prevent memory leaks or any potential problem.
For example, I have an Activity that host a VideoView. The videoPath passed to the Activity will be passed to the Presenter to a VideoUtility to trim the original video into a shorter one before getting passed back to the Activity to be played with the VideoView.
Here’s the confusion: I don’t know where is the appropriate place to call the trimVideo() method as it essentially only need to happen once (unlike in the Android Architect Blueprint, the task is updated with latest data, and thus it’s put in the onResume()).
Please see the code snippet below:
VideoEditorContract:
public interface VideoEditorContract {
interface View extends BaseView<Presenter> {
void playTrimVideo(String trimmedVideoPath);
}
interface Presenter extends BasePresenter {
}
}
VideoEditorActivityBase:
public class VideoEditorActivityBase extends AppCompatActivity implements VideoEditorContract.View {
private VideoEditorContract.Presenter mPresenter;
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_video_editor);
String videoPath = getIntent().getStringExtra(RequestCode.EXTRA_VIDEO_PATH);
mPresenter = new VideoEditorPresenter(videoPath, this);
}
#Override
public void onResume(){
super.onResume();
mPresenter.start();
}
#Override
public void playTrimVideo(String trimmedVideoPath) {
final VideoView vv = findViewById(R.id.act_video_editor_videoView);
vv.setVideoPath(trimmedVideoPath);
vv.setOnPreparedListener(new MediaPlayer.OnPreparedListener() {
#Override
public void onPrepared(MediaPlayer mp) {
vv.start();
}
});
}
#Override
public void setPresenter(VideoEditorContract.Presenter presenter) {
//do nothing as this activity has already init a presenter
}
}
VideoEditorPresenter:
public class VideoEditorPresenter implements VideoEditorContract.Presenter {
private final VideoEditorContract.View mVideoEditorView;
#NonNull
private String mVideoPath;
public VideoEditorPresenter(#NonNull String videoPath, #NonNull VideoEditorContract.View videoEditorView) {
mVideoPath = checkNotNull(videoPath);
mVideoEditorView = checkNotNull(videoEditorView, "videoEditorView cannot be null!");
mVideoEditorView.setPresenter(this);
//trimVideo(); //should I do it here since this task is only need to be done once
}
#Override
public void start() {
//trimVideo(); //I can do it here but then I need to introduce a control variable; not sure if this is the best practice
}
private void trimVideo() {
//trim video stuff
}
// Currently it doesn't have a stop() method. But if it have one,
// what should I put in it? Releasing and clean up the
// VideoUtility I suppose?
}

I got the answer from Francesco Cervone in Medium about this matter (his article is also an excellent resource on MVP, btw. Very well in tune with the Android Architect Blueprint). I leave the relevant bit here for future reader.
Hi, thank you.
Well, I think that the video should be trimmed in the Presenter#start(). Then, after the video has been trimmed, the presenter should call view.playTrimmedVideo(). You shouldn’t do anything in the presenter constructor.
I suppose the video “editing” is something expensive, so you should do that in a separate thread (using for example an async task). You need to implement the Presenter#stop() method because you have to cancel ongoing operations if there are any, unless you retain the presenter.
You said that the trimVideo should be called just once. You could cache/persist in some way the result of trimVideo so that if the video has been already trimmed, you use it.
I hope I answered your question.
"Could you elaborate more on why shouldn’t we put anything in the Presenter’s constructor? I’ve seen the Presenter’s bare minimal constructor in a couple of places but I don’t understand the reason behind it."
First, it’s a responsibility problem: you are going to create an instance of Presenter, and I don’t think that the video editing is something that belongs to the construction of that object.
Second, you don’t know when the presenter is being instantiated, so you shouldn’t execute expensive tasks in the constructor. If you use some dependency injection framework, the construction of the Presenter would be managed by the framework itself and it needs to be efficient. The construction of other objects could depend on the presenter one.

Getting callback even when screen rotates in android (MVP Design Pattern)

Okay, this might be stale, but i really need to understand what the best practice will be and not how to easily bypass this either by disabling screen orientation or any other means.
I have a login screen and when the user clicks on login button it should go to the server and authenticate and return a response.
My problem is if the screen rotates my fragment might not receive a callback of the response data.
I'm trying out an MVP design pattern on android.
public void registerSignInEvent(){
this.signInBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String username = usernameEdit.getText().toString();
String password = passwordEdit.getText().toString();
authPresenter.loginUser(username, password, 1);
}
});
}
I've thought of the following...
Use a service to handle the login to the server, when its done the service updates the storage e.g is_login=false or true then use a LocalBroadcastManager to broadcast the event to the view(Fragment)
so it can query the presenter to know the login state.
Use a Fragment with setRetainIntance(true); to handle the presenter initialization and the presenter will trigger callback to methods of the activity e.g onLoginSuccess //confusing myself
Problem
A. the problem with my no.1 thought is that when my loginFragment is onPause at that moment, the broadcast receiver is unregistered, so it might not receive the event. plus i don't even know if it makes sense.
B. Its looks complicated with MVP pattern
The pattern really might not matter, i don't really need code snippet tho, I just need to understand the process that best fits the situation.
NOTE: My Presenter communicates with the view(fragment/activity) via the view interface, vice-versa.

You could try storing the user in the database/sharedprefs whenever you receive the response from the login, if a rotation occurs and the login-fragment gets reattached without receiving the necessary callbacks (which is the problem you're describing) you could add a check if the user is "already" logged in (by checking if the user exists in the db/sharedprefs in onResume of the loginactivity) and forward the user to the next activity or fragment from there.

First of all I use this cool method to keep presenter alive even if activity recreated: Presenter surviving orientation changes with Loaders. It detaches and attaches activity in onStop and onStart.
Need to mention also, that your second choice with persistent fragment in widely used, e.g. by Fernando Cejas. I've learned clean architecture approach with his articles, and he uses setRetainState(true).
And still your question is driving me crazy as well. Only solution I've found so far is ugly as hell. But it should work. Idea: after work done, I check if view is attached. If so, I proceed normally. I there is no view, that we are in the middle of rotation. So I have flag, that indicate, that work is done. I turn it on. Also I cache any needed data. And wait for the next view attaching. Where I check that flag.
Here is my code snippet. I'm not proud of it thought.
class SplashPresenter extends BasePresenter<SplashView> {
private final SplashInteractor splashInteractor;
private boolean isSplashWorkStarted;
private boolean isSplashWorkFinished;
private boolean isSplashWorkError;
private Throwable splashWorkError;
#Inject
SplashPresenter(SplashInteractor splashInteractor) {
this.splashInteractor = splashInteractor;
}
#Override
public void attachView(SplashView mvpView) {
super.attachView(mvpView);
if (isSplashWorkFinished) {
getMvpView().showApplicationUi();
} else if (isSplashWorkError) {
getMvpView().showError(splashWorkError.getMessage());
}
}
void executeSplashWork() {
if (!isSplashWorkStarted) {
splashInteractor.execute(new SplashInteractorSubscriber());
isSplashWorkStarted = true;
}
}
#Override
public void onDestroyed() {
splashInteractor.unsubscribe();
}
private final class SplashInteractorSubscriber extends Subscriber<Void> {
#Override
public void onCompleted() {
if (isViewAttached()) {
getMvpView().showApplicationUi();
} else {
isSplashWorkFinished = true;
}
}
#Override
public void onError(Throwable e) {
if (isViewAttached()) {
getMvpView().showError(e.getMessage());
} else {
isSplashWorkError = true;
splashWorkError = e;
}
}
#Override
public void onNext(Void v) {
}
}
}

Android robust threading Architecture? Asynctask vs thread/handler vs service/thread

Let's say you're designing the threading architecture for a an app -> the primary purpose is that your app will have a lot of tasks that need something done on the background thread, and sometimes a result task on UI thread, or something not (though more times, the result needs to be run on UI thread). For simplicity, let's say the tasks will be stuff like: download a file and display a pop-up, log a user in and go to a different page, process an image and store the result in a database (popular tasks that a lot of apps do)
I've researched a lot about the nuances, but would really like a deep-dive explanation/knowledge on what kind of architecture is better, and what are the considerations.
here are the three models in consideration:
AsyncTask model: each operation (like downloading a file and displaying a pop-up) is an AsyncTask, or some derivative of a parent class that abstracts out the common functionalities.
Thread/handler model: i always create a new Handler(Looper.getMainLooper()); and each time i need to do a task, i use a thread factory to spin off the task, with the handler on UI thread (or whatever custom handler).
Service/Thread model: i use a general Service class that is in charge of operations based on some operation code. there's a bunch of ServiceTask derivative objects that do certain things, but the Service class communicates with each ServiceTask when tasks are started/done.
I'm slightly leaning towards going the whole service/threading model, just because i've read some really awkward nuances with AsyncTask/Threads:
AsyncTask has a private static handler, and if the classloader calls it at the wrong time (such as including a library that uses it before your application does) then all of your onPostExecute will happen at the wrong time since your handler was not the main handler
it's easy to forget to check a bunch of things in the onPostExecute such as if there was a config change, or your activity was destroyed, or application was backgrounded/paused when the onPostExecute is called (leading to crashes)
AsyncTask changed its serial/parallel execution behavior on different APIs
If you went with the Thread/Handler model, on older devices, thread priority is actually incredibly low. i've heard something like there was a priority scale of 1-15 such that your threads automatically get a low priority and if the system was low on resources, your threads would stop running (whereas since services are running independently of your activity the thread priority there is higher?)
What is the best way to design a robust threading architecture that doesn't easily lead to crashes/unexpected behavior while also maintaining good performance ??
Please also let me know in the comments if this question is too vague and if you need actual code (i'm afraid to post code because it would super overbloat the question length more than it already is).

I don't think you will find a one-size fits all approach here.
Downloading a file? Use DownloadManager
Logging a user in and go to next screen? Probably an AsyncTask would be best.
Process an image and store it? A Service might be a good choice here since you don't want the action to be attached to any particular Activity.
Handlers are more tricky, if they are attached to a Looper running on a background thread you need to call quit() on the Looper when you are done with it. Handlers are good when you need to delay an action, postDelayed() is great for that. They are also good when you need to communicate back to the UI thread from a background thread.
But yes you are correct that each one has pitfalls as you mentioned. Android is a complex beast and it seems they could have a done a better job preventing developers from shooting themselves in the foot, especially in regards to AsyncTask being called after an Activity is destroyed!

I was using Java's old school approach by creating a class (I called it ThreadRunner) derived from Java's Thread. A constructor looked like:
public ThreadRunner (Object [] params, AbstractCallback callBack) {...}
AbstractCallback was a class that was implemnting a single 'onCall' method and was mostly used to notify a calling party about an event such as "execution of a task is completed".
I've used it to get content from Internet and run other time consuming operations. It didn't cause any problems and worked as expected.
However, I've heard many times that AsyncTask is an Android-ish way of doing things like that. I don't know why and do not have any intention to change, since I'm preaching "don't fix it if it's not broken" approach.
I've seen also comments that you'll need to write less code with AsyncTask, but in my approach with traditional Java's Threat the amount of coding was small as well, so I queses it's just a matter of your personal preferences and experience.
In regard of your 3-rd approach - I think you should use it when write a service that runs all the time, listens on requests and never stops. When you just need to execute a single task asynchronously Java Threads or AsyncTask should be used.

I think AsyncTask is a good tool for listed purposes. But it needs to wrap AsyncTask for an easy using. My variant of such wrapping (with a progress indicator) is a following:
Main class AsyncActivity for extending it in application activities:
public abstract class AsyncActivity extends Activity{
// Поле нужно обязательно объявить как статическое!
private static AsyncConnect asyncConnect = null;
protected void runBackgroundTask(String progressInscription, RequestTask task){
asyncConnect = new AsyncConnect(this, responseListener, progressInscription, task);
asyncConnect.execute();
}
protected abstract void onBackgroundTaskEnd(boolean result);
#Override
protected void onResume(){
super.onResume();
// Перерегистрируем текущий контекст этой формы
// для корректной работы слушателя ответа с сервера
responseListener.registerCurrentContext( this );
if (asyncConnect != null){
asyncConnect.onResume(this);
}
}
#Override
protected void onPause(){
super.onPause();
if (asyncConnect != null){
asyncConnect.onPause();
}
}
/**
* Чтобы диалоги не вызывались из устаревшего контекста
* и по этой причине не исчезали при повороте экрана,
* слушателя ответа с сервера необходимо сделать статическим полем класса,
* в котором должен быть зарегистрирован текущий контекст
*/
private static final OnServerResponseListener responseListener = new OnServerResponseListener(){
private AsyncActivity context = null;
#Override
public void registerCurrentContext(AsyncActivity context){this.context = context; }
#Override
public void onResponse(boolean result){
// Если никакой контекст не был зарегистрирован, ничего не делаем
if (context == null) return;
// Освождаем статическое поле для сборщика мусора (но делать это не обязательно!)
asyncConnect = null;
// Вызываем колбэк о завершении фоновой задачи
context.onBackgroundTaskEnd(result);
}
};
}
Additional class and a pair of interfaces:
public class AsyncConnect {
private final Activity context;
private final RequestTask task;
private final String progressInscription;
private final OnServerResponseListener responseListener;
private boolean isDone = false;
private ProgressDialog progressDialog;
public AsyncConnect(Activity context, OnServerResponseListener responseListener,
String progressInscription, RequestTask task){
this.context = context;
this.task = task;
this.progressInscription = progressInscription;
this.responseListener = responseListener;
progressDialog = null;
isDone = false;
}
public void execute(){
if (isDone) return;
new ConnectTask().execute();
}
public void onPause(){
if (isDone) return;
if (progressDialog != null){
if (progressDialog.isShowing()){
progressDialog.dismiss();
progressDialog = null;
}
}
}
public void onResume(Activity context){
if (isDone) return;
progressDialog = ProgressDialog.show( context, null, (CharSequence)progressInscription,
true, false);
}
private class ConnectTask extends AsyncTask<Object, Void, Boolean> {
#Override
protected void onPreExecute( ) {
super.onPreExecute();
progressDialog = ProgressDialog.show( context, null,
(CharSequence)progressInscription, true, false);
}
#Override
protected Boolean doInBackground(Object... messages) {
return task.call();
}
#Override
protected void onPostExecute(Boolean result) {
super.onPostExecute(result);
if (progressDialog != null){
if (progressDialog.isShowing()){
progressDialog.dismiss();
progressDialog = null;
}
}
// Делаем невозможным повторное использование этого объекта
isDone = true;
responseListener.onResponse(result);
}
}
}
public interface OnServerResponseListener {
public void registerCurrentContext(AsyncActivity context);
public void onResponse(boolean result);
}
public interface RequestTask {
public boolean call();
}
For using AsyncActivity we only need to call runBackgroundTask and implement onBackgroundTaskEnd in the target activity. It's possible to create different kinds of AsyncTask wrappings based on this idea.

You may also check out Needle; it's an open-source, simple but powerful multithreading library for Android. With it you can say things like:
Needle.onMainThread().execute(new Runnable() {
#Override
public void run() {
// e.g. change one of the views
}
});
or
Needle.onBackgroundThread().execute(new UiRelatedTask<Integer>() {
#Override
protected Integer doWork() {
int result = 1+2;
return result;
}
#Override
protected void thenDoUiRelatedWork(Integer result) {
mSomeTextView.setText("result: " + result);
}
});
very simple API
fixed thread pool size
customizable thread pool size
supports UI interaction ("do work and then use result on UI thread")
android 1.5+
behaves the same on all platform versions
Check it out on GitHub: https://github.com/ZsoltSafrany/needle

Own Listener change UI-Thread in Android

#first Sorry for my bad english.
I have created a own Listener. I want to change a TextView, when the Listener is called in the MainActivity from a Service. The idea for my own Listener is from:
http://tseng-blog.nge-web.net/blog/2009/02/17/how-implement-your-own-listener-android-java/
In the Code Example the TriggerMethod() ist called from a Calculation Thread, running in the Service.
I solved the Problem, but I find, it isn't pretty nice, because in every new Activity I have to make a new Thread. Is it possible to create an interface/listener that automatically can change the UI?
Used to solve the Problem:
http://developer.android.com/guide/components/processes-and-threads.html
ResultListener.java:
public interface ResultListener {
public void onResultAvailable(double result);
}
SimuService.java:
public class SimuService extends Service {
private ResultListener mResultListener = null;
public void setResultListener(ResultListener listener){
mResultListener=listener;
}
public void triggerMethode(){
observeResultDouble=getObserveDouble;
mResultListener.onResultAvailable(observeResultDouble);
}
MainActivity:
public class MainActivity extends FragmentActivity{
TextView txtView;
ResultListener mResultListener;
SimuService mSimuService;
protected void onCreate(Bundle savedInstanceState) {
txtView = (TextView) findViewById(R.id.txtServiceTime);
//Create Service .....an Bind
mResultListener = new ResultListener() {
#Override
public void onResultAvailable(double result) {
txtView.setText("Result: "+result);
}
};
mSimuService.setResultListener(mResultListener);
}
MY SOLUTION:
ResultListener = new ResultListener() {
#Override
public void onResultAvailable(double result) {
this.result=result;
runOnUiThread(setNewDataToUI);
}
};
private Thread setNewDataToUI = new Thread(new Runnable() {
#Override
public void run() {
txtView.setText("Result: "+result);
}
});

First of all: If you reference a Service in an Activity, the Service becomes pretty much useless. The advantage of services are, that they are loose coupled and can work indepenendtly form activities (=what the user sees) and its lifecycle and might even be in their own process. Thus activity-service communication is through intents or inter-process language AIDL, not through callbacks. If you want something executed asynchronosly use AsyncTask.
To your main problem: as you found out, you can only modify the UI on the UI-thread. So by design, leave changing UI in the component, thats responsibly for that (either activtiy or fragment), that will prevent the need of runOnUiThread()
Your code seems like txtView.setText("Result: "+result); will be executed in the Activity, but it wont. It will be executed in the Service, which (as I impleied before) does not run on the UI-thread. The problem is, I dont get the intent, what exactly you want to achieve so it is hard to give you an alternative solution.

Android - Concurrency problems on multiple activity restarts

When doing an orientation change in the emulator (ADT v17.0.0), or on a device (original Droid), I noticed that the activity will go through more than one create-destroy cycle sometimes. I found this blog post that mentions the problem, but offers no solution.
My app (API 8) currently does a 'last-chance' save of user data in onPause, and retrieves that data in onCreate/onStart, which works fine for a single restart, but gets into concurrency issues if the cycles come back-to-back. Specifically if a load starts before a save is complete, the 'last-chance' data is lost.
I did read the Faster Screen Orientation Change Android-developer article which mentions transferring an Object via onRetainNonConfigurationInstance/getLastNonConfigurationInstance. I tried using onRetain/getLast... like a flag to tell if the activity is "restarting", which works, but I still have the main issue of not knowing if/when any existing save/load operations are completed.
Concurrency & thread-management are not my strongest suits, so I'm looking for a solution that does at least one save & load across any number of back-to-back restarts, without memory leaks. Since fast create-destroy cycles could happen for non-orientation reasons, ideas that just involve breaking/handling orientation changes alone aren't really what I'm after.
Here's a log file excerpt with some cycles, you can see where the activity gets created-destroyed twice when going from landscape to portrait. Here's an excerpt of what I've got now:
onPause() {
file_manager.saveTemporaryPattern(); // writes to OutputStream on UI thread
}
onStart() {
findViewById (R.id.main_screen).post (new Runnable() {
file_manager.loadTemporaryPattern(); // reads from InputStream on UI thread
});
if (getLastNonConfigurationInstance() != null) {
// DO SOMETHING HERE?
}
}
onRetainNonConfigurationInstance() {
return dummy_object;
}

Managed to solve the concurrency issue by sending the Load/Save calls to a Handler thread linked to the Application context, rather than the Activity context. Had to setup a Load vs Save token in the calls to check for a Save->Load->Save pattern, avoiding the odd behavior of getting an incomplete activity lifecycle on a landscape->portrait orientation change.
It works in development & on test devices, and doesn't leak the activity context, so we'll see how it does in the wild.
In YourApp extends Application:
private Handler fileAccessThread = null;
public void onCreate() {
super.onCreate();
if (fileAccessThread == null) {
fileAccessThread = new Handler();
token = 0;
}
}
public void postCallbackFileAccess (int _token, Runnable _callback) {
switch (_token) {
case TOKEN_SAVE:
// Save must follow load, not another save
if (token == TOKEN_SAVE) { return; }
token = _token;
break;
case TOKEN_LOAD:
// Have to allow load->load, otherwise data gets lost/deleted
// if (token == TOKEN_LOAD) { return; }
token = _token;
break;
}
fileAccessThread.post (_callback);
}
In YourActivity:
protected void onStart() {
super.onStart();
((YourApp) getApplication()).postCallbackFileAccess (
YourApp.TOKEN_LOAD, new Runnable() {
#Override
public void run() {
file_manager.load();
}
});
}
protected void onPause() {
super.onPause();
((YourApp) getApplication()).postCallbackFileAccess (
YourApp.TOKEN_SAVE, new Runnable() {
#Override
public void run() {
file_manager.save();
}
});
}