I wrote a script to simulate the user actions. The workflow is, for example, first tap an icon, launch an activity. Then do other actions.
The question is , I don't know the exact time that the activity launched completely. At present, I use sleep to make my script wait.
Is there any way to know when an activity launched completely?
I dont know what exactly you want to do when the activity started. But normally everyones requirement is to find width of a view or something to do with the UI. The thing is, onCreate is called before the UI is drawn so nothing related to the UI that involves measuring can be done here. For that we can use a global layout listener.
ViewTreeObserver vto = outerLayout.getViewTreeObserver();
vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
#Override
public void onGlobalLayout() {
outerLayout.getViewTreeObserver().removeGlobalOnLayoutListener(this);
//This is executed once the layout is drawn. AFAIK this is as close as it gets
to when the activity is started.
}
});
Is your final task is to run something after activity is launched... do this
First method called from activity is onCreate() , Hence we can say completing the onCreate() system calls onStart() which calls onResume() method... as onResume() completes you can say your activity is launched properly...
If you are not going to override onStart() or onResume() what I am going to describe can be written as last statements of onCreate(). That's I usually do when I don't need onStart() or onResume().
You can create an object of Handler. Like
Handler handler = new Handler();
Handler has a method postDelayed() that is called some times after the creating and launching is finished.
call it like
handler.postDelayed(runnable,timeInMilliSeconds);
after all the processes finish, application will wait for timeInMilliSecondsms to start the process defined in run method of runnable provided in postDelayed .....
Thus
If your task is to know when the launching is finished the answer is: at the end of onResume() called from your onStart() ....
If you want to perform some action use handler.PostDelayed() method and keep timeInMilliSeconds very low... [between 1 to 10].
Related
When I start my android-activity first onCreate() is called, then onResume().
When I then press the back-button to return to the home-screen and tap the app-icon again, first onCreate() is called, then onResume() and then onDestroy().
My app is still active then, but doing some action result in error since onDestroy() sets a few members to null.
Why is that?
Update: When I wait 30 seconds after pressing back everything works fine. I'm not doing anything heavy in onDestroy except setting a few variables to null and .interrupt()ing a background-thread.
Figured this out by myself. My understanding of what an Activity is was flawed. Of course Android calls onDestroy() on the old Activity instance, which can happen several seconds after the new one has been constructed.
onDestroy gets called because, by default, pressing back key results in your activity calling finish() which initiates the destroying of the activity which calls onDestroy().
To prevent doing some action in case the activity is being destroyed do like this:
if(!isFinishing()) {
// do your action here
}
isFinishing is a method of the Activity.
are you doing some heavy operations in onDestroy(). I think your activity view is destroyed, but not the activity object. And you tap on the App icon even before the previous Activity object is actually destroyed.
I think there is something in addition to what you are describing. Android doesn't just keep activity from being destroyed, something MUST be happening on the main thread.
The symptoms sound exactly as if you had either:
a service doing a longish HTTP or database operation. Are you sure there are no suxg things?
another thread (perhaps managed by an AsyncTask?) calling a synchronized method
How do I properly do that?
I have a stopwatch and I'm saving it's state in onSaveInstance and restoring it's state in onRestoreInstance...
Now I've following problem: if I stop the thread in onSaveInstance and the screen get's locked or turned off, onRestoreInstance is not called and the stopwatch is not continuing...
If I don't stop it, the stopwatch is running in background on and on even when the screen is off or the activity is not active anymore...
So what's the usual way to handle such a thing?
PS:
I even have a working solution, a local variable to save the running state in the onStop event and restarting the thread in the onStart event... But I still want to know if there's a "default" solution using the android system itself....
Ok. I better now understand what you're doing. I thought you were using the thread to count. Right now it sounds like you're using it to update the UI.
Instead, what you probably should be doing is using a self-calling Handler. Handlers are nifty little classes that can run asynchronously. They're used all over the place in Android because of their diversity.
static final int UPDATE_INTERVAL = 1000; // in milliseconds. Will update every 1 second
Handler clockHander = new Handler();
Runnable UpdateClock extends Runnable {
View clock;
public UpdateClock(View clock) {
// Do what you need to update the clock
clock.invalidate(); // tell the clock to redraw.
clockHandler.postDelayed(this, UPDATE_INTERVAL); // call the handler again
}
}
UpdateClock runnableInstance;
public void start() {
// start the countdown
clockHandler.post(this); // tell the handler to update
}
#Override
public void onCreate(Bundle icicle) {
// create your UI including the clock view
View myClockView = getClockView(); // custom method. Just need to get the view and pass it to the runnable.
runnableInstance = new UpdateClock(myClockView);
}
#Override
public void onPause() {
clockHandler.removeCallbacksAndMessages(null); // removes all messages from the handler. I.E. stops it
}
What this will do is post messages to the Handler which will run. It posts every 1 second in this case. There is a slight delay because Handlers are message queues that run when available. They also run on the thread that they're created on, so if you create it on the UI thread you will be able to update the UI without any fancy tricks. You remove the messages in the onPause() to stop updating the UI. The clock can continue to run in the background, but you won't be showing it to the user anymore.
I just got into Android programming, but I don't think onRestoreInstance will be called in that situation because you're not switching from one activity to another. I think your best bet is to call onPause which will then call onSaveInstance if you need it to, but use onResume which might or might not call onRestoreInstance.
I'm developing an Android 3.1 application.
I want to execute an AsyncTask after activity is shown. I want to show something to user before execute AsyncTask.
I've read that it is not recommend to execute AsyncTask on onCreate().
Where I have to execute AsyncTask on onStart() or onResume()?
I want to left enough time to show activity before execute it.
onCreate(), onStart() and onResume() are lifecycle methods called by the operating system and shouldn't be called directly. You can however override them to have your code executed at these stages of the activities lifecycle:
However, if you want your AsyncTask to start after all of your Views have been inflated and drawn to the screen then you need to put the code in this:
toReturn.getViewTreeObserver().addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
public void onGlobalLayout() {
toReturn.getViewTreeObserver().removeGlobalOnLayoutListener(this);
// asyncTask.execute();
}
});
In the above example toReturn is a view in your onCreate() method. It can be any view you like.
This pulls a ViewTreeObserver from the View and add's a listener to it which will be called when the view has finished being drawn to the screen. It's important you keep the "removeGlobalOnLayoutListener()` line in as this will stop the code firing every time the View is drawn.
Answer is in onResume()
I hade same requirement in my activity where i need to show some list with other buttons and images..
List were getting data from server so used AsyncTask for that..
But before that required to show empty listview and other part of the screen..
so first when it goes to onCreate() I set empty arraylist to listview's adapter then in onResume() call the Asynctask and in that task fill the ArrayList and call adapter.notifyDataSetChanged()
Then another problem occure..when i go to next activity and come back it always call the asynctask even if i dont require..
So had put some condition like if(arrayList.size()==0) then call asynctask else dont.
You can put yur code in the onWindowsFocusChanged method. You can use a thread inside it to manage the timer to start your specific asynctask.
Be aware that this would be performed each time your activity have the focus, not only the first time you launch your activity (I don't know if this could be a problem for you).
implement a View object and override the onDraw().
that way you'll know exactly when the first screen is visible to the user
How can i create/bind a service only after activity layout is rendered?
-- Update
I have two tabs (both as separate activities)on the main activity and the data used for tabs comes from Service. Right now i'm binding service inside onCreate method. Issue is that layout is not rendered till all the statements inside the onCreate gets finished. A blank screen is shown till the service get bind
See ViewTreeObserver
More info here: https://stackoverflow.com/a/7735122/338479
Put the call to create/bind the service at the end of your onCreate activity. If it must absolutely bind/create at the very end of the process, you can add a boolean flag to your activity indicating whether you are already bound or have already created the service. You could then override onResume() as follows:
#Override
public void onResume() {
super.onResume();
if (!flag) {
// Call code to bind/create the service.
}
}
I have a START and STOP button in the main screen of an App. there are some GUI and threads that are instantiated when I click on START. When I click on stop, I want everything to be stopped and the activity should come back to its origin state. To the state that is exactly same like when launched (when we tapped on App icon in mobile).
Is it possible to do this? I tried with finish() , this killed the app and exited . I don't want to exit from main screen. rather, on clicking STOP I want app to come back to origin or born state. Thanks.
How are you running your threads? Are they vanilla threads or subclasses of AsyncTask?
If these are instances of an AsyncTask object, you can use the cancel() method to cancel it and then inside your doInBackground() method, you could check the isCancelled() method to see if it has indeed been canceled, and then exit gracefully.
Pseudo code below:
private YourTask taskRef;
public void btnStartHandler() {
taskRef = new YourTask();
taskRef.execute();
}
public void btnStopHandler() {
taskRef.cancel();
}
and then, in your AsyncTask:
public Void doInBackground(Void... arg0) {
// Background loop start
if (this.isCancelled()) {
return;
}
// Background loop continue...
}
If you're using threads, you can interrupt them and catch the exception and handle it there. Furthermore, you could create a method that you call from onCreate() called initApp() or something that initializes everything. You could also use that initApp() from the STOP button click handler to reset values back to startup defaults.
You can restart the activity with finish() and then call startActivity(getIntent());. This will effectively restart your activity and put it in its default state, no matter how it was started.
Before doing that make sure to cancel all threads or AsyncTasks as TJF suggested (you can and should do this in the onDestroy overload).
For more info about restarting an activity, and a discussion about pros and cons, see this question: Reload activity in Android