I have an app that has three activities, the user will be constantly tabbing between these three activities. Right before the user closes the app, my code downloads the current time from the internet and stores it. The problem is that i have my code for downloading the time in the onPause() method. This causes the data to be downloaded over and over each time the user switches activities. I tried using onDestroy() but the download would never start. is there a method that is called when the user minimizes or closes the app altogether instead of one that is called on an activity switch?
Thank you very much, any help is appreciated!
We can achieve this using the Application class. There we can implement the ActivityLifecycleCallbacks to identify when our app goes to the background and based on that result we can perform our required task. Here, a sample code:
public class MyApplication extends Application implements ActivityLifecycleCallbacks {
private Handler mHandler;
#Override
public void onCreate() {
super.onCreate();
mHandler = new Handler();
}
...
#Override
public void onActivityResumed(Activity activity) {
Log.i("Activity Resumed", activity.getLocalClassName());
// cancel scheduled download operation (if any)
mHandler.cancelCallbacksAndMessages(null);
}
#Override
public void onActivityPaused(Activity activity) {
Log.i("Activity Paused", activity.getLocalClassName());
// schedule a download operation after 5 seconds
mHandler.postDelayed(new Runnable() {
#Override
public void run() {
performDownloadOperation()
}
}, 5000);
}
... // other lifecycle callbacks
private void performDownloadOperation() {
// perform download operation here
}
}
In the above code, we are basically giving the user [and the system] a grace time of 5 seconds to switch from one activity to another. Otherwise, we note that the app went to background and do our stuff there. So, even if the user switches to a different app for 4 seconds and then come back, we'd still not download the data, which should be fine in most cases.
Note that to use the above class, you need to provide the class reference to the android:name property as android:name=".MyApplication" under the <application> tag in the manifest file.
You can make use of Activity::isFinishing(). This will return false when you (1) launch another activity or when (2) the app is put on background, but it will return true when (3) the back button is pressed or if (4) somebody calls finish on the activity.
If it is important to distinguish between (1) and (2), then you can always keep a flag that you can switch every time you launch an activity and reset it in onPause.
Related
My current Android Application needs to call
ActivityManager.clearApplicationUserData()
to simulate the user clearing App storage
Which works fine.
A side effect of calling clearApplicationUserData() is that the App is (understandably) closed.
Which gives a poor user experience.
I am having difficulty in restarting my Application once I have called clearApplicationUserData().
I have tried using startActivity, Alarm Manager with Pending Intent, Foreground/Background service.
Nothing works.
Is it impossible to restart an Android App having called clearApplicationUserData()?
(1st answer: this answer only works on limited situations. it's not a complete answer)
public boolean clearApplicationUserData ()
Description
Return: true if the application successfully requested that the application's data be erased; false otherwise.
As the reference website stated, we have a returnee before the application is being closed. so, we are going to use this returnee in order to restart the app.
if(ActivityManager.clearApplicationUserData)
{
doRestart = true;
}
when Activity onDestroy() and onStop() are called restart app.
#Override
protected void onDestroy() {
super.onDestroy();
if(doRestart){
Intent intent = new Intent(this, Activity.class);
this.startActivity(intent);
}
}
#Override
protected void onStop() {
super.onStop();
if(doRestart){
Intent intent = new Intent(this, Activity.class);
this.startActivity(intent);
}
}
We put restart action in both onDestroy() and onStop() in order to make sure the app will be restarted again.
And also, I think it's a good idea to force stop activity before OS stops it.
if(ActivityManager.clearApplicationUserData)
{
doRestart = true;
finish(); <= i mean this
}
it's because it makes sure that onDestroy() and onStop() will be invoked.
My suggestion might sound trivial but, have you consider not calling ActivityManager.clearApplicationUserData()?
Here what the docs says about this method:
Permits an application to erase its own data from disk. This is
equivalent to the user choosing to clear the app's data from within
the device settings UI. It erases all dynamic data associated with the
app -- its private data and data in its private area on external
storage -- but does not remove the installed application itself, nor
any OBB files.
So in order to mimic this behavior you just need to clear you internal and external storage directories. No permissions are needed to access any of those.
(2nd answer: I need much more contribution on it)
After 8 hours of researching in Android OS and Android Developers Website in order to find a solution to restart activity when clearApplicationUserData is invoked. Finally, I would be able to find a nice/hacking solution.
This solution looks like Zidane dribble :)
Let's introduce the solution. at first, clearApplicationUserData clears all the clues of the application when is invoked like tasks, notifications, alarms and etc. therefore, explicit Activity calling is impossible.
implicit way is the only possible way of calling activity.
After a couple of tests I found that application manifest registered intent-filters wouldn't be removed and they are able to listen for incoming system broadcasts.
Approximately, 98% of system broadcasts wouldn't be received by cleared application and that 2% remained might not be broadcasted very soon.
so what to do? hmmm? come on man I must find a solution ...
bingo, ** I must trigger something in order to system broadcast it** <= looks hacking :)
so I decide to choose WIFI_STATE_CHANGED because
Easy Access permission
System Broadcasts it on delay <= this makes sure that the app is closed
before broadcast
manifest.xml
<receiver
android:name=".PackageDataClearedReceiver"
android:enabled="true"
android:exported="true">
<intent-filter android:priority="100">
<action android:name="android.net.wifi.WIFI_STATE_CHANGED" />
<action android:name="android.net.wifi.STATE_CHANGE" />
</intent-filter>
</receiver>
MainActivity.java
public class MainActivity extends AppCompatActivity {
ActivityManager am;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
AppCompatButton btn = findViewById(R.id.btn);
btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
new Thread(new Runnable() {
#Override
public void run() {
am = (ActivityManager) getApplicationContext().getSystemService(Context.ACTIVITY_SERVICE);
if (am != null) {
ExecutorService pool = Executors.newFixedThreadPool(2);
final Collection<Future> futures = new HashSet<Future>();
futures.add(pool.submit(new Runnable() {
#Override
public void run() {
WifiManager wifiManager = (WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);
wifiManager.setWifiEnabled(true);
wifiManager.setWifiEnabled(false);
am.clearApplicationUserData();
}
}));
for (Future future : futures) {
future.isDone();
}
}
}
}).start();
}
});
}
}
demo
keep in mind, it's just A minimum viable product that needs to be developed more in order to make it work perfectly.
Clearing the app data on the device through the API clearApplicationUserData() resets the app as if it were just installed. As you have found, any alarms and broadcasts registered with your app are also cleared. The most efficient way to keep your app in the foreground would be to clear the data yourself, as others have pointed out, rather than using the API. Here is an example: https://stackoverflow.com/a/9073473/949224
However, if you are determined to use the API (which does guarantee all data is cleared) and the app is force-stopped, I have a suggestion:
Create a small companion app that can be launched just prior to you clearing your app data. The companion app simply re-launches your app, possibly after a short time-out.
Intent launchIntent = getPackageManager().getLaunchIntentForPackage("example.com.testrelaunchapp");
if (launchIntent != null) {
startActivity(launchIntent);//null pointer check in case package name was not found
} else {
Log.w( TAG, "Unable to resolve launch activity of relauncher companion app");
}
((ActivityManager)getSystemService(Context.ACTIVITY_SERVICE))
.clearApplicationUserData();
The companion app itself needs to close afterwards, and ideally should be hidden from the Activity Stack etc..
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final Intent launchIntent = getPackageManager().getLaunchIntentForPackage("example.com.yourmainapp");
if (launchIntent != null) {
Handler handler = new Handler(getMainLooper());
handler.postDelayed(new Runnable() {
#Override
public void run() {
Log.i( TAG, "About to act on launchIntent");
launchIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
launchIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
launchIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
startActivity(launchIntent);
finish();
System.exit(0);
}
}, 1000);
}
}
I have seen this work with Android 6.0, but no guarantees it would be versatile and work across the board. There would be more to do to make the companion app UI-less if desired and to be hidden from the phone's launcher. You would also probably want to bundle the APK as a file within your own app and install it upon first run, which would need the user to enable installation from "Unknown sources" (non-Play store). It can be done through intents to the right System settings, if needed, but users would need a good explanation why this is needed.
So, as I was saying, the simpler approach is to clear the data and app permissions yourself.
I have a Raspberry Pi 3 running Android Things. For simplicity, assume it only rotates a stepper motor.
To again simplify things, the stepper motor is rotated by telling coil by coil which ones to charge and which ones not to charge. In a Raspberry Pi you connect four output pins to four input pins of the stepper motor. Then you fire up the pins one by one in a continuous sequence with some milliseconds between each run.
If I stop the program in Android Studio by pressing Stop 'MainActivity' the program code gets killed but the output pins in the Raspberry Pi still stay charged. In my case, if I stop the program in Android Studio, one of my stepper motor coils remains charged (and gets overheated).
QUESTION: What is the best way to do clean-up in Android before the program shuts down?
I have tried onDestroy() and onPause() but neither of those are guaranteed to be called when the program closes. (They also have never worked in my case).
I have also tried to add a shutdown hook but even that doesn't turn off the output pin. The shutdownhook, which is located in MainActivity's onCreate() method, looks like this below:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Runtime.getRuntime().addShutdownHook(new Thread(){
#Override
public void run(){
try{
mRobotics.stopMotor();
} catch (Exception e){
// Ignore error
}
}
});
// onCreate continues...
The method stopMotor() looks like this:
public void stopMotor(){
this.motorHandler.removeCallbacksAndMessages(null);
try {
mStepper1.setValue(false);
mStepper2.setValue(false);
mStepper3.setValue(false);
mStepper4.setValue(false);
} catch (Exception e){
// Nothing here
}
}
There are a lot of related questions on, for example, stopping threads when the program closes but I haven't found anything from StackOverflow that works in my case.
You are correct that clicking the Stop button in Android Studio simply terminates your application process without calling any of the life cycle methods. The same is true if your application crashes or Android needs to terminate your app due to memory pressure, so it's something that can happen at runtime as well. There are no hooks you can add to anticipate every time this may happen.
One option is to move your motor driver logic into a separate app module and control it through a bound service. This way, when the main app terminates (either during development or due to a crash), the driver app can manage that appropriately. It's also generally a good separation of concerns to separate your driver code from your main app this way.
Here's an example of what that might look like:
driver.apk
class MotorDriverService : Service() {
override fun onCreate() {
super.onCreate()
startMotor()
}
override fun onDestroy() {
super.onDestroy()
stopMotor()
}
}
main.apk
class MainActivity : Activity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val intent = ...
bindService(intent, connection, Context.BIND_AUTO_CREATE)
}
override fun onDestroy() {
super.onDestroy()
unbindService(connection)
}
private val connection = object : ServiceConnection {
override fun onServiceConnected(className: ComponentName, service: IBinder) { }
override fun onServiceDisconnected(name: ComponentName) { }
}
}
The reason this works better is because bound service connections are automatically managed. Android creates the service when the activity wants to bind to it, and destroys it when there are no more clients bound (which in this case would also happen in the main.apk terminates or crashes).
The driver and main have to be two separate apps (not an activity/service in the same APK) because this only works if the two run in completely separate processes.
I know for an activity you can override onStart on onStop methods to know when an activity starts / exits. The issue I'm running into is I want to keep a session open from when a user opens the app until it enters the background / user exits and tying into onStop (for end session) for each activity isn't giving the the results I want, it ends the session every new activity. So I was wondering what are my options for knowing when a user puts the app in the background or exits.
One thing I thought of is keeping track of onStart and onStop (or any two combinations in the activity life cycle) so I know if I have a onStop without a onStart right before the app is exiting. This seems very hacky, not sure if its the right place to start.
Thanks for any input.
You can extend Application class and use registerActivityLifecycleCallbacks to build the logic.
Using for example these two callbacks:
#Override
public void onActivityResumed(Activity activity) {
mBackground = false;
}
#Override
public void onActivityPaused(Activity activity) {
mBackground = true;
}
https://developer.android.com/reference/android/app/Application.html#registerActivityLifecycleCallbacks(android.app.Application.ActivityLifecycleCallbacks)
I am using AsyncTask to post some status on social media.
private class PostOnSocialMedia extends AsyncTask<String, Void, String> {
#Override
protected void onPreExecute() {
pDialog.setTitle(R.string.posting_status_on_social_media);
Log.d(TAG, "onPreExecuteCalled.");
}
#Override
protected String doInBackground(String... params) {
Log.d(TAG, "doInBackground.");
currentActivity.this.twitter.tweet(params[0]);
currentActivity.this.facebook.post(params[0]);
currentActivity.this.googlePlus.share(params[0]);
return null;
}
#Override
protected void onPostExecute(String result) {
if (pDialog.isShowing()) {
pDialog.dismiss();
}
// Start next Activity when posted on all social media.
Intent intent = new Intent(currentActivity.this,
nextActivity.class);
intent.putExtra("userMatches", userMatches);
startActivity(intent);
Log.d(TAG, "onPostExecute.");
}
}
When user is not logged in to, lets say, Twitter I have to start a new Intent to show twitter page(so that user can log in). This causes the flow to return back to AsyncTask and calls a onPostExecute() method. And new Activity is started.
But I don't want this. What I want is that user login to Twitter and then it will come back to application (when user clicks login flow comes back to current activity. But the activity is created as a new one not the one from which I started a call to social medial post). When it comes back to application, I call a method of Twitter class to proceed to complete the uncompleted posting task. And once it is done, then only I want to go to next activity.
So, is there anyway to handle this situation?
EDIT :
Is it possible to solve this by using onSaveInstanceState(Bundle savedInstanceState) and onRestoreInstanceState(Bundle savedInstanceState)?
before calling asynctask make sure your user is logged in on both platforms, then call asynctask, because now in this case there are lots of combinations of a user can do, so my suggestion is first make sure user is logged in on both facbook, tiwtter etc. then call this asynctask so you dont have to make the asynctask wait
AsyncTask used for background Process.
So you have to check All the condition before calling asynctask and then used.
Generally, AsyncTasks are to do stuff in background without blocking the UI-Thread. If you want your Main-Thread (= UI-Thread) to wait for your AsyncTask, you could just do it without an AsyncTask.
If you want to wait for it though, try yourTask.get();, that should make your Main-Thread wait for the result of your Task. Look here for more info about get().
I solved my problem by using a static variable which is set to true just before recreating an Activity and when Activity execution is in onCreate I use this variable to decide whether this activity is recreated and if yes, then call method to perform remaining task.
When posting is done I call a method of activity, which calls a method to post on social media, from Twitter class where post is successfully done.
Method in activity :
public static void postDone() {
// Go to next activity
}
Call from Twitter class :
MyActivity.postDone();
The title explains all... I have this snippet of code in my application:
String url = createTelUrl("3112007315");
Intent intent = new Intent(Intent.ACTION_CALL);
intent.setData(Uri.parse(url));
context.startActivity(intent);
It does make a call, but once the call ends, my application crashes. I'd like to return to my application once the call has finished, but I read this post and it seems not to be possible. So... is there anyway to at least pause my application and resume it once the call has finished?
EDIT:
Thanks for the two answers I received, I feel I'm really close to my goal... I had already done some of the things you guys suggested. But, maybe I didn't explain some details of the application... I'm developing Who Wants To Be A Millonarie game, so I need to implement calls (I don't know how it's called in USA or other countrys, but here we call it "call to a friend").
Anyway... I've done too many changes to this app and now it's not crashing. But, the Canvas where I draw the UI is not been showed once the called has ended.
I have a SurfaceView that holds the UI. For that SurfaceView I created a thread that is meant to refresh the UI... this is basically what the thread does:
#Override
public void run() {
Canvas c;
while (_run) {
c = null;
try {
c = _surfaceHolder.lockCanvas(null);
// Check if should wait
synchronized (_surfaceHolder) {
_panel.onDraw(c);
}
} finally {
// do this in a finally so that if an exception is thrown
// during the above, we don't leave the Surface in an
// inconsistent state
if (c != null) {
_surfaceHolder.unlockCanvasAndPost(c);
}
}
}
}
But, once the call has ended I get a black screen. The surface is there (I know it because it still can receive some touch events), but it's not showing anything. Another thing to take in account is how I'm starting the Thread from the SurfaceView class:
public void surfaceCreated(SurfaceHolder holder) {
hilo.setRunning(true);
try{
hilo.start();
}catch(IllegalThreadStateException ite){
Log.e("wwtbam", "god dammed");
}
}
This worked nice before I start implementing phone-calls. The problem here is that once the call has ended and it executes again the start method which throws a IllegalThreadStateException because the thread has already been started. I've tried using some 'technics' to pause the UI thread while calling but I haven't been able to solve this problem. I tried doing something like:
// this in the UI thread class
if(haveToWait)
wait();
....
// this in the surface view class
if(callEnded)
hilo.notify();
But that didn't work. I also have tried some other 'tricks' like using sleep(50); instead of wait(); but it does not work either.
With all that information I provided... what could you suggest to me?
The problem here is the place you're using to start the thread. Once you start a new call, your main activity will be paused and the surfaceview will be destroyed. Though, the thread will keep running. So, once your app takes the control back, the surface is created again and the start method will be invoked. That causes a IllegalThreadStateException.
The way to go here is to manipulate the thread out of the SurfaceView class. That will give you the control of the thread from the main activity, and you will be able to decide when to start or pause your thread.
Take a look of this example: http://code.google.com/p/apps-for-android/source/browse/trunk/SpriteMethodTest/src/com/android/spritemethodtest/
This is possible using an android.telephony.PhoneStateListener.
First, we need to take care of the manifest of the app:
We need the permission to make calls (duh!) as well as the permission to watch the phone state. The latter is needed so the app can react to the ending of a call as well. So we add these lines to out application manifest:
<uses-permission android:name="android.permission.CALL_PHONE" />
<uses-permission android:name="android.permission.READ_PHONE_STATE" />
Also, we don't want Android to start a different instance of our activity when the call has ended, so we set the launchMode attribute of the activity to "singleInstance".
<activity android:name=".CallTest" android:label="Calling Test"
android:launchMode="singleInstance" />
Having prepared everything in the manifest, we can now look at the activity making the call:
public class CallTest extends Activity {
PhoneStateListener mListener;
TelephonyManager mTelMgr;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mListener = new CallEndedListener();
mTelMgr = (TelephonyManager) this.getSystemService(TELEPHONY_SERVICE);
}
public void makecall(View v) {
// Register our listener to be notified of the beginning
// and ending of calls
mTelMgr.listen(mListener, PhoneStateListener.LISTEN_CALL_STATE);
// Start the call
Intent call = new Intent(Intent.ACTION_CALL);
call.setData(Uri.parse("tel:12345"));
startActivity(call);
}
class CallEndedListener extends PhoneStateListener {
boolean called = false;
#Override
public void onCallStateChanged(int state, String incomingNumber) {
super.onCallStateChanged(state, incomingNumber);
// Don't fire before the call was made
if (state == TelephonyManager.CALL_STATE_OFFHOOK)
called = true;
// Call has ended -- now bring the activity back to front
if (called && state == TelephonyManager.CALL_STATE_IDLE) {
called = false;
mTelMgr.listen(this, PhoneStateListener.LISTEN_NONE);
startActivity(new Intent(CallTest.this, CallTest.class));
}
}
}
}
The only new thing in the makecall method, compared to the code snippet in the question, is the PhoneStateListener implementation added right before actually making the call. This listener then gets notified by Android when an outgoing call is dialed, an incoming call is ringing or when an active call is ended.
Our implementation waits for the latter CALL_STATE_IDLE event and starts our activity again, so that after the call has ended we're back in our app where we left it. It then deregisters itself, so our activity doesn't get restarted every time the user ends a call not initiated by our own activity.
However, when registering for the CALL_STATE-events with the TelephonyManager, Android instantly fires a notification with the current status -- so our listener would get triggered before the call had even started. Therefore our listener implementation first waits until an outgoing call was started (CALL_STATE_OFFHOOK) and only after that happened reacts to the CALL_STATE_IDLE notification.
HTH!
As for the crash - please post the log and put your debugger onStart/onResume to find out why you're crashing. It's possible that something is initialized in the wrong place and you might something as simple as nullpointer.
As for the call end thing - i've never try this, but i'd try to register receiver, catch
http://developer.android.com/reference/android/telephony/TelephonyManager.html#ACTION_PHONE_STATE_CHANGED
Evaluate the state of the phone and do what you need to do .
Also there is more info here
http://developer.android.com/reference/android/telephony/
http://developer.android.com/reference/android/telephony/PhoneStateListener.html
And finally you'll find examples of how to use that in the applications that are use that functionality in source.android.com