In my Android app I have two activities: Activity A and Activity B. The first one (A) starts the second one (B) with startActivity().
If the user hits the back button, I'd like Activity B to pass an object back to Activity A before it's destroyed. The only thing I can come up with is to override onBackPressed() in Activity B and save the object in SharedPreferences, then retrieve the object from SharedPreferences in Activity A's onResume(). Can anyone recommend a more elegant solution?
Thanks a lot!
Related
It seems each activity has its own Fragment Manager but I have a situation when I need to access the Fragment Manager of a previous activity. Here is the situation. I have tabs A - E launching Activities A - E in each tab. Each activity have fragments. So I am in Fragment B1 (in Activity B launched by Fragment A3 of Activity A) and I want to go back to A3 but since A3 is in another Activity, I can't use popBackStack on BackPress because Activity B doesn't know (can't access) the BackStack of Activity A. How do I get back to A3 of Activity A from B1 of Activity B. Thanks
See when one activity calls another activity, the caller activity's instance state is saved in stack so if you want to go back from called activity to the caller fragment try calling finish(); in the back pressed method and it will do the trick for you.eg
#Override
onBackPressed{finish();}
I have two activities
Class MainActivity{
//has a single button and
//invokes SubActivity
}
Class SubActivity{
//This activity several textfields
}
While SubActivity is alive, I press back button and go back to MainActivity.
When I go back to MainActivity again, I would like to get the textfield values from the MainActivity. I tried using context but it doesn't seem to work. Any suggestion is welcome.
You either have to pass them in a bundle with the intent to start the activity, write them to shared preferences, or put them in sqlite database. It's not possible to simply read data from another activity.
I'm trying to minimize memory usage in my app, and one of the things I'm doing is calling finish() in the onPause method (which I know is not the best way to do things). For the most part, it seems to be working well, but when the user clicks the back button from the next activity, it logically skips over the finished activity and goes back further. Is it possible to have that activity in the back stack and just get recreated if the user presses back?
No. This conclusion comes from the task and backstack documentation as well as the activity documentation and a general understanding of how a stack data structure works.
A stack data strucure only has 2 possible operations push/put, which adds something to the collection, and pop, which removes it. Stacks folow a last in first out model, or LIFO, where by last thing added - in your case an activity - is the first thing removed when pop is called.
Within the android lifecycle activities are generally popped from the stack when the back button is pressed. At that point onDestroy() is called and the activity is removed (you can verify this by overriding the onDestroy() method and logging the results if you want to check). Alternativly you can force onDestroy() to be called by calling finish() as you are. Finishing an activity effectivly does the same thing as pressing back. The activity is destroyed and must be recreated before it can be added to the stack.
For what you're trying to do the stack would have to incorporate some intermediate state in which an activity does not exist but rather something akin to a reference is held that, when moved to the top, would indicate that the corresponding activity should be recreated. Since this is not how the sack works - it only holds activities - that state cannont exist and so the result you are talking about is not possible.
Your Goal is to minimize memory usage,Just make use of activity life cycle, You can do this alternative(if you need)
-Just leave onCreate() method blank.(only do setContentView(layout))
-Override onResume();
-whatever you were doing in onCreate just copy paste to onResume().
-and In onPause(), Recycle your all bitmaps and set them to null(I think you are using Bitmaps thats why you are very cautious about it ). and remove your views.
Now what will happen, when you launch your new activity, onPause() would be called. that will remove your all bitmap and views. and when you come back, onResume() will be call.(onCreate will not be called). and that will again initialize your view and bitmaps.
No, i don't think that is possible. Once you finish the Activity it's gone. You could, however, implement and handle your own stack. On back pressed, you would just start the closed Activity again.
I have five activity in my app,
Act1->Act2->Act3->Act4->Act5,
All activity goes in single direction as I have stated above,
Now I have to call again Act2 after successful completion of my Act5's task, so its working good and showing me the Act2 (I have Used startActivity(callIntent) in Act5 for showing me Act2 again),
After this when I click on Back button in Act2, I have Act1 (I have Used startActivity(callIntent) in Act2 for showing me Act1 again) its what I want .....
But the problem is that when I click Act1's back button it is going to put me on Act2. But I want to exit from there, because Act1 is the first initial activity.
How Can I set focus to my hidden activity , instead of creating Intent and call startActivity.
Any idea? Please help.
After long research I got pretty much understanding of "back stack" for all the activities in an app.
Each time I moved to another activity and also for opening previous activity I have used Intent.startActivity() with flag FLAG_ACTIVITY_NEW_TASK, So every time I have new activity added in the "back-stack".
I have tried intent flag as FLAG_ACTIVITY_CLEAR_TOP while calling previous activity from "back-stack" using Intent.startActivity() and I got the solution of calling back the previous activity and clears all stack top activity above the calling one activity. So now back button does working nice as I needed.
Let see My problem of calling previous activity ,
A = activity; A1->A2->A3->A4->A5->B2 , now if you click on back button you will have A1 activity , and after clicking on A1's back button you have again B2 activity which was called after A5 and so on.
After using the FLAG_ACTIVITY_CLEAR_TOP in A5 activity and called again A2 (Not creating new activity but calling precious one) I have following situation.
A = activity; A1->A2->A3->A4->A5
calling previous A2 activity, and I have following scenario.
A1->A2 only.
Thanks.
Instead of following code (with flag Intent.FLAG_ACTIVITY_NEW_TASK):
Intent callIntent = new Intent(Intent.ACTION_CALL);
callIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
callIntent.setClass(CurrentActivity.this,PreviousActivity.class);
startActivity(callIntent);
Try using following one with Intent.FLAG_ACTIVITY_CLEAR_TOP
Intent callIntent = new Intent(Intent.ACTION_CALL);
callIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
callIntent.setClass(CurrentActivity.this,PreviousActivity.class);
startActivity(callIntent);
In the application activities are stacked like this: A - > B - > C - > D - > E.
If I receive a particular notification and click on it, Activity E is started.
If I then click back (button on phone or button on actionbar), the application exit.
How do I make the transition to Activity D in this case, and then back through C, B, and A?
My code of back button:
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
finish();
break;
}
return true;
}
Everything is okay when starting the application normally. The problem is when Activity starts from the notification.
Android has the functionality you're after built in, and it is already well documented. To begin with you should look at the TaskStackBuilder class. It was introduced in JellyBean, but is already included in the support library, and you use it to build a synthetic TaskStack which is what you need. A summary from the documentation reads:
When crossing from one task stack to another post-Android 3.0, the application should synthesize a back stack/history for the new task so that the user may navigate out of the new task and back to the Launcher by repeated presses of the back key. Back key presses should not navigate across task stacks.
TaskStackBuilder provides a way to obey the correct conventions around cross-task navigation.
How you build it is going to depend on the relationships of the Activities in your app, but the Tasks and Back Stack developers guide is a good read to help you decide, as is the Navigating with Up and Back design guide, if this is all new to you.
You'll find some code examples in the Implementing Effective Navigation lessons, also on the Android developers site, in the training section.
Incidentally, the button on the ActionBar is referred to as Up. Even though it sometimes shares the same functionality as the back button, the two are not the same (I assume that's the one you are talking about ;-) .)
I think you can solve your problem by sending an intent from Activity E to Activity D, and so on.
Therefore you should overwrite the method
onBackPressed()
that is called when you click on the back button.