I have a class in a service
MyClass m = new MyClass();
and inside my class I check if I have permission to overlay the view; if so, it's ok, otherwise I must start an activity
if (Settings.canDrawOverlays(mContext)) {
// draw over app
} else {
// start the activity
Intent i = new Intent(context,Calls.class);
context.startActivity(i);
}
When I start the activity I have a problem communicating between the class and the activity. I know how to use the interface but how can I register it in activity.
Some time I want to pass an object or data from the class to the activity or from the activity to the class... how can I do that?
I saw many examples in Stack Overflow about how to communicate between service and activity; they suggest to start the class from the activity but this does not work in my app because my class must be running all the time.
Perhaps you could use an event bus like mechanism where you can send or receive events through out your app, Though there are several libraries out there, I would recommend using Otto library for android.
Usage is pretty simple just register in your activity onCreate
Bus bus = new Bus();
bus.register(this);
For sending events
// example data to post
public class TestData {
public String message;
}
// post this data
bus.post(new TestData().message="Hello from the activity");
And subscribe to events like this
#Subscribe public void getMessage(TestData data) {
// TODO: React to the event somehow!
}
More info here
If you want to implement a communication pattern between a Service and an Activity, you should use a LocalBroadcastManager.
It will turn handy because, in case your Service is still on but your Activity
has been destroyed (very common situation), then the 'messagging' between the two will simply have no effect (no NPE or whatsoever will be thrown).
Step 1
Create a BroadcastReceiver in your Activity and define an ID / Filter
this.localBroadcastReceiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
// Do what you have to do here if you receive data from the Service / Background Task
}
}
public static final IntentFilter SIGNAL_FILTER = new IntentFilter("com.you.yourapp.MY_SIGNAL")
Step 2
In your Activity register the broadcast in onResume() and unregister it in onPause().
#Override
protected void onResume() {
// Listen if a Service send me some data
LocalBroadcastManager.getInstance(getApplicationContext()).registerReceiver(this.localBroadcastReceiver, SIGNAL_FILTER);
}
#Override
protected void onPause() {
// I'm going to the background / or being destroyed: no need to listen to anything anymore...
LocalBroadcastManager.getInstance(getApplicationContext()).unregisterReceiver(this.localBroadcastReceiver);
}
Your Activity is now ready to receive data from any other component in your Application.
If it's in the background, then there is no need to update the UI: in fact the Activity will not respond if in the background.
In the same way, if it's being garbage collected, the Receiver will be unregistered and the Activity will just not respond to anything.
If the Activity is resumed / restarted, onResume() will be triggered and the Receiver will be registered again.
Step 3
All you need to do right now, is send data from the Service.
Simply call
final Intent intent = new Intent();
intent.setAction(SomeActivity.SIGNAL_FILTER);
// put your data in intent
LocalBroadcastManager.getInstance(getApplicationContext()).sendBroadcast(intent);
and your Activity will accordingly respond to the signal.
It's surprising how few people know about the LocalBroadcastManager and instead use some self-implemented callback / singleton pattern, which increases complexity and non-readability.
This pattern is built-in in Android, so you don't need external libraries. As for security, this ensures that your signals stay internal to your application: no data can therefore be read by other apps.
I similarly answered to another question here.
Related
Case is after I got a response from my async task, I want to show a DialogFragment.
But if user put the application to background while the app still waiting for the response, on the moment the response came and .show DialogFragment it will crashed.
I've done immediate fix by try catching the .show, but the DialogFragment won't show after user return to the app.
Is there a clean way to let the application keep on showing DialogFragment while on background or on the next onResume ?
The only way I found while googling is using an ActivityDialog, but it will require much effort.
Edit : Eh I actually able to show it now with commitStateLoss ._.
from
customErrorDialog.show(((FragmentActivity) context).getSupportFragmentManager(), "TAG");
to
((FragmentActivity)context).getSupportFragmentManager().beginTransaction().add(customErrorDialog, "TAG").commitAllowingStateLoss();
idk if this is dangerous for some specific case though
You should use lifecycle-aware components to receive response.
For android-java projects simply use livedata. Base on the document:
LiveData is lifecycle-aware, meaning it respects the lifecycle of other app components, such as activities, fragments, or services. This awareness ensures LiveData only updates app component observers that are in an active lifecycle state. LiveData considers an observer, which is represented by the Observer class, to be in an active state if its lifecycle is in the STARTED or RESUMED state.
For android-kotlin projects, you have more options than java. You can still use livedata like Java. Other options are StateFlow, which is part of the flow and coroutines. Collecting them with repeatOnLifecycle. Base on document:
public class NameActivity extends AppCompatActivity {
private NameViewModel model;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Other code to setup the activity...
// Get the ViewModel.
model = new ViewModelProvider(this).get(NameViewModel.class);
// Create the observer which updates the UI.
final Observer<String> nameObserver = new Observer<String>() {
#Override
public void onChanged(#Nullable final String newName) {
// Update the UI, in this case, a TextView.
nameTextView.setText(newName);
}
};
// Observe the LiveData, passing in this activity as the LifecycleOwner and the observer.
model.getCurrentName().observe(this, nameObserver);
}
}
StateFlow and SharedFlow are Flow APIs that enable flows to optimally emit state updates and emit values to multiple consumers.
You can find this behavior in other observable classes like LiveData
class LatestNewsActivity : AppCompatActivity() {
private val latestNewsViewModel = // getViewModel()
override fun onCreate(savedInstanceState: Bundle?) {
...
// Start a coroutine in the lifecycle scope
lifecycleScope.launch {
// repeatOnLifecycle launches the block in a new coroutine every time the
// lifecycle is in the STARTED state (or above) and cancels it when it's STOPPED.
repeatOnLifecycle(Lifecycle.State.STARTED) {
// Trigger the flow and start listening for values.
// Note that this happens when lifecycle is STARTED and stops
// collecting when the lifecycle is STOPPED
latestNewsViewModel.uiState.collect { uiState ->
// New value received
when (uiState) {
is LatestNewsUiState.Success -> showFavoriteNews(uiState.news)
is LatestNewsUiState.Error -> showError(uiState.exception)
}
}
}
}
}
I have three java files in my Android project. Two are activities (MainActivity and GeoActivity) and one is a plain java file (PostHttp -> sends data to server via the HTTP POST)
I switch over to GeoActivity via a simple button on-click method. GeoActivity returns the co-ordinates of the current location in a TextView AND sends them to a remote server via the HTTP POST.
I have a Handler.class which executes sends the Post Message after a delay of 50s. Something like this below. The problem i have is that when i click the back button and switch over to MainActivity i can still see in LogCat the echoes receiving from the server that the data is still being sent. How can i stop that?
GeoActivity.class
public class GeoActivity extends Activity {
Location location;
private Handler mHandler = new Handler();
protected void onCreate(Bundle savedInstanceState) {
....
if(location != null){
mHandler.postDelayed(updateTask,0);
}
...
}
...
public Runnable updateTask = new Runnable(){
public void run(){
mlocListener.onLocationChanged(location);
//send coordinates with a delay of 50s
new PostHttp(getUDID(),latitude,longitude).execute();
mHandler.postDelayed(updateTask, 50000);
}
Try acting on the activity's life cycle.
For example:
#Override
protected void onStop() {
super.onStop(); // Always call the superclass method first
// Save the note's current draft, because the activity is stopping
// and we want to be sure the current note progress isn't lost.
ContentValues values = new ContentValues();
values.put(NotePad.Notes.COLUMN_NAME_NOTE, getCurrentNoteText());
values.put(NotePad.Notes.COLUMN_NAME_TITLE, getCurrentNoteTitle());
getContentResolver().update(
mUri, // The URI for the note to update.
values, // The map of column names and new values to apply to them.
null, // No SELECT criteria are used.
null // No WHERE columns are used.
);
}
This doesn't destroy the activity, it will reside in memory. However, you can always resume when needed.
Source:
Stopping and Restarting Android Activities
i am developing an app with phonegap 2.2. I have been able to implement a background service from https://github.com/Red-Folder/Cordova-Plugin-BackgroundService.
right now i want to be able to listen for changes in the contacts database such that when a change is detected, a function can run in the background service (Java Method).
How can this be implemented.
You have to create a content observer in your service and register that observer to listen for changes in contacts database.
Here is an example of contacts content observer:
ContactsContentObserver contentObserver = new ContactsContentObserver();
private class ContactsContentObserver extends ContentObserver
{
public ContactsContentObserver()
{
super(null);
}
#Override
public void onChange(boolean selfChange)
{
super.onChange(selfChange);
// handle change received
}
}
You can register the content observer in service onStart() method:
getContentResolver().registerContentObserver (ContactsContract.Contacts.CONTENT_URI, true, contentObserver);
And unregister it in service onDestroy() method:
getContentResolver().unregisterContentObserver(contentObserver);
Hope it helps.
How can I send an orderedBroadcast to a specific receiver? I am broadcasting the ACTION_MEDIA_BUTTON and only want a specific app (Winamp for example) to receive it. I don't want Pandora to steal it. Is there a way to explicitly define who the receiver will be?
void sendBroadcast() {
Intent i = new Intent(Intent.ACTION_MEDIA_BUTTON);
synchronized (this) {
i.putExtra(Intent.EXTRA_KEY_EVENT, new KeyEvent(KeyEvent.ACTION_DOWN, theKeyEvent));
ctx.sendOrderedBroadcast(i, null);
i.putExtra(Intent.EXTRA_KEY_EVENT, new KeyEvent(KeyEvent.ACTION_UP, theKeyEvent));
ctx.sendOrderedBroadcast(i, null);
}
}
If you know the package of the Winamp application, you can use setPackage to restrict Intent resolution to only a specific package.
I've been wondering if it is possible to use an IntentService to do some networking while keeping the queue of pending intents prioritized. My goal to be able to download some images in the background, add more if needed (send another Intent) and be able to reset the queue if necessary (preferably using a specific Intent). That is all possible with an IntentServie but when I send that 'stop' Intent it needs to be processed as the next item in the queue, not the last where it is right now.
EDIT
For those interested I have taken the AOSP code for IntentService and modified it to meet my needs. The reason I cannot just subclass IntentHandler is because of the private ServiceHandler class inside of IntentHandler.
Inside of the ServiceHandler I have a new method:
public final boolean sendPriorityMessage(Message msg)
{
int priority = msg.arg2;
//Log.i(GenericList.TAG,"recieved message priority: "+priority);
if(priority>PRIORITY_NORMAL){
return sendMessageAtFrontOfQueue(msg);
}else{
return sendMessage(msg);
}
}
This method is called from onStart instead of just sendMessage
#Override
public void onStart(Intent intent, int startId) {
Message msg = mServiceHandler.obtainMessage();
msg.arg1 = startId;
msg.obj = intent;
try{
msg.arg2 = intent.getExtras().getInt(KEY_PRIORITY);
}catch(Exception e){
msg.arg2 = PRIORITY_NORMAL;
}
mServiceHandler.sendPriorityMessage(msg);
}
Overall the code is still limited but I am able to fast track some messages to the front of the queue, which is what I was after anyway.
you could implement/extend your own PriorityQueue that simply checks every new intent added to the queue. if it's the stop intent, it moves it straight to the front of the line.