Develop Reference

Android Access Same instance method on activity from different threads without locking. Added synchronized method

I have a method goToNextScreen() which does a check for 3 different asynchronous process, so when all process are done the validation will changes activity (Is kind of a Splash activity)
My example code access from 3 different result callbacks to the activity's method goToNextScreen() updating the flag value for each process and to validate other flags inside.
So far this approach works but i have the next questions:
Is this approach valid? Does it have a risk for some kind of deadlock? all threads/callbacks won't collide accessing the method at the same time causing wrong validations?
class LoadingActivity extends Activity{
public boolean isFetchDone, isAnimationDone, isServiceDone, watchDog;
Presenter presenter;
protected void onCreate(#Nullable Bundle savedInstanceState) {
presenter(this);
runAnimation();
presenter.runGetXService();
runFetchFromDB();
}
//do some generic isAnimationDone
private void runAnimation(){
//animator set and animation assumed to be correct...
//...
animatorSet.addListener(new Animator.AnimatorListener() {
#Override
public void onAnimationStart(Animator animation) {
// do anything before animation start
}
#Override
public void onAnimationEnd(Animator animation) {
isAnimationDone = true;
goToNextScreen();
}
#Override
public void onAnimationCancel(Animator animation) {
// do something when animation is cancelled (by user/ developer)
}
#Override
public void onAnimationRepeat(Animator animation) {
// do something when animation is repeating
}
});
}
//Some example function to fetch data from x DB
private void runFetchFromDB() {
final Realm realm = RealmProvider.getInstance();
final ThingDB db = new ThingDBImpl(realm);
realm.beginTransaction();
db.getData(10L)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Subscriber<XData>() {
#Override
public void onCompleted() {
isFetchDone = true;
goToNextScreen();
}
#Override
public void onError(Throwable e) {
//we dont care about the result
isFetchDone = true;
goToNextScreen();
}
#Override
public void onNext(XData dataSaved) {
//Should i update isFetchDone here?
});
realm.cancelTransaction();
}
private synchronized void goToNextScreen(){
if(!watchDog) return;
if(isFetchDone && isAnimationDone && isServiceDone){
changeActivityFaded(this, SomeOtherActivity);
finish();
watchDog = true;
}
}
}
class Presenter {
Activity activity;
Presenter(Activity activity){
this.activity = activity;
}
public void runGetXService(){
new Presenter.GetServiceAsyncTask().execute();
}
private class GetServiceAsyncTask extends AsyncTask<Void, Void, Response> {
#Override
protected void onPreExecute() {
super.onPreExecute();
//do preparation for service response, etc, asumme all correct
}
#Override
protected XResponse doInBackground(Void... voids) {
try {
return //Assume correct behaviour...
} catch (NetworkConnectionException e) {
return null;
}
}
#Override
protected void onPostExecute(XResponse xResponse) {
super.onPostExecute(xResponse);
((LoadingActivity)activity).isServiceDone = true;
((LoadingActivity)activity).goToNextScreen();
}
}
}
EDIT:
I have changed the method goToNextScreen to synchronized so it supposed to not allow access from others threads at the same time. Still have doubts if withs the execution will be right.

Yes, making the method synchronized means it cannot be executed multiple times simultaneously. If a second thread calls it while it is still executing, the second thread will block until the synchronization lock is released.
https://docs.oracle.com/javase/tutorial/essential/concurrency/syncmeth.html

So far this approach by adding the synchronized to the method goToNextScreen member of the activity instance shared on the threads accessing it has worked so far. (View the question code for solution). Although i need to add a watch dog just in case some thread pass to execute code that its supposed to execute just once.

Android exception when popping backstack

This is a followup question to these questions:
popBackStack() after saveInstanceState()
Application crashes in background, when popping a fragment from stack
I am creating an application which uses a service and is reacting to events which are created by the service. One of the events is called within a fragment and is popping from the backstack like this:
getSupportFragmentManager().popBackStack(stringTag, FragmentManager.POP_BACK_STACK_INCLUSIVE);
When the app is in the foreground it works fine. When the app is in the background, I get an
IllegalStateException: Can not perform this action after onSaveInstanceState
I have already tried overriding onSaveInstanceState with an empty method.
Why do I get this exception only when the app is in the background and how can I solve it?

Try something like this.
public abstract class PopActivity extends Activity {
private boolean mVisible;
#Override
public void onResume() {
super.onResume();
mVisible = true;
}
#Override
protected void onPause() {
super.onPause();
mVisible = false;
}
private void popFragment() {
if (!mVisible) {
return;
}
FragmentManager fm = getSupportFragmentManager();
fm.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
}
}
when you implement the above code alone when you resume the app you will find yourself in a fragment that you actually want to be popped. You can use the following snipped to fix this issue:
public abstract class PopFragment extends Fragment {
private static final String KEY_IS_POPPED = "KEY_IS_POPPED";
private boolean mPopped;
#Override
public void onSaveInstanceState(Bundle outState) {
outState.putBoolean(KEY_IS_POPPED, mPopped);
super.onSaveInstanceState(outState);
}
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (savedInstanceState != null) {
mPopped = savedInstanceState.getBoolean(KEY_IS_POPPED);
}
}
#Override
public void onResume() {
super.onResume();
if (mPopped) {
popFragment();
}
}
protected void popFragment() {
mPopped = true;
// null check and interface check advised
((PopActivity) getActivity()).popFragment();
}
}
Original Author

Socket disconnect as soon as it connects in android

i am trying to create group chat android application and used Websocket server written in php. this server work fine on Web browser but when i try to use it in android application application disconnect as soon as it connects.
here Android code:
public class MainActivty extends Activity{
private WebSocketClient mWebSocketClient;
private ListView mMessageListView;
private ArrayAdapter<String> mAdapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_layout);
mMessageListView=(ListView)findViewById(R.id.listView);
mAdapter=new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1);
mMessageListView.setAdapter(mAdapter);
connectWebSocket();
}
private void connectWebSocket(){
URI uri;
try {
uri=new URI("ws://192.168.0.102:9000");
mWebSocketClient=new WebSocketClient(uri){
#Override
public void onOpen(ServerHandshake serverHandshake) {
}
#Override
public void onMessage(String s) {
}
#Override
public void onClose(int i, String s, boolean b) {
}
#Override
public void onError(Exception e) {
}
};
mWebSocketClient.connect();
} catch (URISyntaxException e) {
e.printStackTrace();
return;
}
}
private void Append_Message(String log){
mAdapter.add(log);
mAdapter.notifyDataSetChanged();
}
}
server console:
server console shows client activity

when i rewrite this code using https://github.com/pavelbucek/tyrus-client-android-test i think i could not satisfied full requirement of previous library that i used. but tutorial on this link have solved my problem.

GoogleApiClient not connected if used from fragment

I discovered a strange behaviour today.
I have my activity which connects to the GoogleApiClient in onStart() and disconnects in the onStop()
The activity uses a GridViewPager to show my fragments. To send messages through the Data Layer i use a callback interface between activity and fragment.
If i call sendMessage() from a button within the Activity layout it works fine. If sendMessage() is executed by the fragment using the callback interface sendMessage() shows the "not connected" Toast.
In both ways the same method in the Activity is called so how is it possible that it behaves different ?
I should mention that the problem only occours after the application is restarted for the first time.
Activity
public class WearPlex extends WearableActivity implements
NavigationRemoteCallbacks,
GoogleApiClient.ConnectionCallbacks,
GoogleApiClient.OnConnectionFailedListener {
private List<Node> nodeList = new ArrayList<Node>();
private List<Fragment> fragmentList = new ArrayList<Fragment>();
private GoogleApiClient googleApiClient;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_wear_plex);
setAmbientEnabled();
fragmentList.add(NavigationRemoteFragment.getInstance(this));
GridViewPager mGridPager = (GridViewPager)findViewById(R.id.gridViewPager);
mGridPager.setAdapter(new MainGridPageAdapter(getFragmentManager(), fragmentList));
googleApiClient = new GoogleApiClient.Builder(this)
.addApi(Wearable.API)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.build();
}
#Override
protected void onStart() {
super.onStart();
googleApiClient.connect();
}
#Override
protected void onStop() {
googleApiClient.disconnect();
super.onStop();
}
#Override
public void onConnected(Bundle bundle) {
Toast.makeText(this, "Connected", Toast.LENGTH_SHORT).show();
nodeList.clear();
Wearable.NodeApi.getConnectedNodes(googleApiClient).setResultCallback(new ResultCallback<NodeApi.GetConnectedNodesResult>() {
#Override
public void onResult(NodeApi.GetConnectedNodesResult nodes) {
for (Node node : nodes.getNodes()) nodeList.add(node);
}
});
}
#Override
public void navigationRemoteSendCommand(String commandPath) {
sendMessage(commandPath, null);
}
public void debugOnClick(View view) {
sendMessage("/debug", null);
}
public void sendMessage(String path, byte[] data) {
if (googleApiClient.isConnected()) {
for (int i = 0; i < nodeList.size(); i++) {
if (nodeList.get(i).isNearby()) {
Toast.makeText(this, "Send message", Toast.LENGTH_SHORT).show();
Wearable.MessageApi.sendMessage(googleApiClient, nodeList.get(i).getId(), path, data);
}
}
} else {
Toast.makeText(this, "Not connected", Toast.LENGTH_SHORT).show();
}
}
#Override
public void onConnectionFailed(ConnectionResult connectionResult) {
Toast.makeText(this, "Connection failed", Toast.LENGTH_SHORT).show();
}
Fragment
public class NavigationRemoteFragment extends Fragment {
private static NavigationRemoteFragment navigationRemoteFragment = null;
private NavigationRemoteCallbacks callbackHandler = null;
private ImageButton navBtnCenter;
public static NavigationRemoteFragment getInstance(NavigationRemoteCallbacks handler) {
if (navigationRemoteFragment == null) {
navigationRemoteFragment = new NavigationRemoteFragment();
navigationRemoteFragment.callbackHandler = handler;
}
return navigationRemoteFragment;
}
public NavigationRemoteFragment() {
// Required empty public constructor
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// Inflate the layout for this fragment
View v = inflater.inflate(R.layout.fragment_navigation_remote, container, false);
navBtnCenter = (ImageButton)v.findViewById(R.id.navBtnCenter);
navBtnCenter.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
callbackHandler.navigationRemoteSendCommand("/debug");
}
});
return v;
}
}
Callback interface
public interface NavigationRemoteCallbacks {
public void navigationRemoteSendCommand(String commandPath);
}
EDIT 1 code for MainGridPageAdapter
public class MainGridPageAdapter extends FragmentGridPagerAdapter {
private List<Fragment> fragmentList = null;
public MainGridPageAdapter(FragmentManager fm, List<Fragment> fragmentList) {
super(fm);
this.fragmentList = fragmentList;
}
#Override
public Fragment getFragment(int i, int i1) {
if (i1 < fragmentList.size()) return fragmentList.get(i1);
return null;
}
#Override
public int getRowCount() {
return 1;
}
#Override
public int getColumnCount(int i) {
return fragmentList.size();
}

You don't show the code for MainGridPageAdapter so I don't know how it is managing fragments. You mention that the problem occurs after a restart. Looking at the code in WearPlex.onCreate(), I suspect that the problem is caused fragments that are holding a reference to an old, destroyed instance of the activity.
A poorly documented behavior of FragmentManager is that it saves its state across restarts. This is often overlooked, resulting in duplicate fragment instances after a restart. The correct pattern for managing fragment creation in the onCreate() method of the host activity is:
if (savedInstanceState == null) {
// Not a restart
// Create a new instance of the fragment
// Add it to the fragment manager
} else {
// Restart
// The fragment manager has saved and restored the fragment instances
// Use findFragmentById() to get the fragment if you need it
}
You are not using savedInstanceState in onCreate() to test for restart. Are you seeing more fragments than you expect after restart? If so, the original fragments are holding a reference to the old activity, which was stopped, and has a disconnected GoogleApiClient. If the NavBtn of one of those fragments is clicked, you will see the "not connected" toast.
Update
The problem is caused by the way you are creating new instances of NavigationRemoteFragment, specifically the use of static member navigationRemoteFragment. After a restart, when the activity is recreated, the code calls NavigationRemoteFragment.getInstance(this). getInstance() finds navigationRemoteFragment not null because it is static, and does not create a new fragment. The fragment returned is the old one, which holds a reference to the old activity, which has been stopped and has a disconnected GoogleApiClient.
This could be confirmed by using the isDestroyed method and adding a some debug logging:
#Override
public void navigationRemoteSendCommand(String commandPath) {
if (isDestroyed()) {
Log.w("TEST", "This is an old instance of the activity");
}
sendMessage(commandPath, null);
}

Otto Subscribe method not called from Activity to Fragment in Another Activity

This is my first activity where Im making a post call. The bus provider is the default one in the otto sample app.
void openNextActivity()
{
manager.bus.post("Hi");
// Intent to my next Activity
}
This is my fragment in another activity where im subscribing for the data. The bus received is the same, however the subscribe method is not being called.
public class ProductListFragment extends BaseFragment {
String LOG_TAG = ProductListFragment.class.getCanonicalName();
public static ProductListFragment newInstance() {
ProductListFragment fragment = new ProductListFragment();
return fragment;
}
public ProductListFragment() {
// Required empty public constructor
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
getActivity().invalidateOptionsMenu();
}
#Override
public void onResume() {
super.onResume();
BusProvider.getInstance().register(this);
}
#Override
public void onPause() {
super.onPause();
BusProvider.getInstance().unregister(this);
}
#Subscribe public void onPostRecived(String s) {
Log.d(LOG_TAG, s);
}
}
There are no errors on anything being received, however if I put a button onclick on the fragment and post some content from there, the subscribe method is being called. For eg.
#OnClick(R.id.makePostCall) void call() {
BusProvider.getInstance().post("Hi");
}
I'm getting the appropriate log on this call. Any idea where the code is going wrong?

it seems you subscribe your second activity's fragment after sending stuff to event bus. Consider changing your logic

u send msg before intent;the BusProvider id registered after intent;
just try:
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
BusProvider.getInstance().post("Hi");
}
},3000);