Develop Reference

back button's function on first activity

Normally when the back button is clicked it goes to the previous activity and if the current activity is the first activity, the application closes.
I have a splash screen (that is logically my first activity) and then the menu activity loads.
I want to close the program when the back button is pressed on my menu activity (as if it is the first activity) and avoid going back to the splash screen again, but I know that I should not exit the program.
I was wondering what is the functionality of back button on the first activity?
does it put the program to pause?

Avoid splash screens !
Instead of using your splash as the main activity, use menu activity as the main one, and in onCreate() chain off the splash activity, which will close and disappear forever.

When new Activity is launched from first Activity, first Activity is executed until onStop() method, then it stops and waits for relaunch, unless you killed it by calling .finish(), in that case launched Activity becomes first Activity and back button will minimize application on back button press. In order to control what application does on back button press you can override this method in your Activities and implement your own custom behaviour:
#Override
public void onBackPressed() {
super.onBackPressed()
}
Very good example of how lifecycle of Fragments/Activities work can be seen in picture below:
Hope this helps. Good luck.

While you are on the SplashScreen, on the method calling your menu activity I assume you are doing something like startActivity (new Intent (this, MenuActivity.class)); in Java or startActivity(Intent(this, MenuActivity::class.java)) for Kotlin just after that call finish() this will remove your SplashScreen from the back stack

add this attribute to your splash activity (in manifest):
android:excludeFromRecents="true"
pressing back in per activity, transfer control to prev activity in stack (back stack) that not excluded from "Recents".

How can I preserve previous android intent value when I press the back or up button?

I have a list view in the previous intent and when I tap on that it go to the next activity. Now when I press the back button or up button it comes back to the previous activity. But when I tap the list item again it give me run time Unexpectedly app closed error. Please help me.

It's hard to answer without code, but maybe it's because you don't finish your next activity when you press the back button

It's because of Activity life cycle...
When you go to the next activity then current activity is paused for you. when you press the back or up button then your previous activity resume.
That's why you have to define your code in onResume() method also where you got stuck. because when you come back onResume method is called

You can try override onBackPressed method in your activities :
#Override
public void onBackPressed() {
// put a breakpoint here and check your listview/activities states
//super.onBackPressed();
}

Android going back to previous activity instead of deleting fragment?

I have 2 activities with fragments inside of them. Whenever I press the back button, the fragment gets destroyed (Used FragmentTransaction's replace method for adding them into the activity) instead of going back to the first activity immediately.
How can I achieve the behavior I want to have?

You can override onBackPressed method in your activity and check if the fragmentManager.getBackStackEntryCount()==0. If yes finish() the activity.
Hope it helps.

How to clear activity stack trace on back press event?

I have created an application that has multiple pages and navigation from one to another represents a crucial flow. I don't want the user to be able to press the back button and escape the activity without first warning him and then finally deleting all stack trace such that when the activity is launched again it starts afresh.
As of yet I have been using something similar to the function below :
#Override
public void onBackPressed()
{
this.finish();
Intent int1= new Intent(this, Home.class);
int1.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(int1);
super.onBackPressed();
}
But sometimes when after quitting the application when I launch it again it restarts from some random page or the one from where I quit the application (basically not the home screen from where it is expected to start)
I cannot think of a cleaner way to quit the application other than clearing all the previous activity flags as described in the code.
Any help on the above is appreciated!
EDIT :
Anytime during the flow of my activity if the user presses the back button, I want the control to be thrown back to the main page (clearing all the previous activity stack traces). Such that in case someone re-lanches the application it will re start normally from the main page.

You don't need any of this custom code in onBackPressed(). All you need to do is add this to all of your <activity> definitions in the manifest (except the root activity):
android:noHistory="true"
This ensures that none of your activities (expect the root activity) is recorded in the back stack. When the user clicks the BACK key, it will just return to the root activity.
Another benefit of this is that if the user leaves your app (by clicking HOME or by pulling down the notification bar and clicking on a notification, when he returns to your app it will also just return to your root activity.

Anytime during the flow of my activity if the user presses the back
button, I want the control to be thrown back to the main page
(clearing all the previous activity stack traces).
This can be done just by finishing all the activities as they move forward, except the MainActivity.
Such that in case someone re-lanches the application it will re start
normally from the main page.
Is it like if user is in Activity_5 and uses Home Button and relaunches the app again, MainActicity must appear?
IF so, you can call finish() in onPause() of every Activity except MainActivity
EDIT:
Might not be the perfect solution, but this is what I did to achieve exactly the same(logout in my application):
OnBackPressed() in any activity updates a boolean shared preference say backPressed to true and in onResume() of all the Activities, except MainActivity check its value and finish if true.
#Override
protected void onResume() {
super.onResume();
SharedPreferences mSP = getSharedPreferences(
"your_preferences", 0);
if (mSP .getBoolean("backPressed", false)) {
finish();
}
}

Back Button is used to go back to the previous activity. So i would not override the back button to clear activity stack. I suggest you use a Action Bar for this purpose. Navigate to Home Screen of the application using the application icon.
http://developer.android.com/guide/topics/ui/actionbar.html
Also check this link and comments below the answer by warrenfaith
android - onBackPressed() not working for me

#Override
public void onBackPressed()
{
moveTaskToBack(true);
android.os.Process.killProcess(android.os.Process.myPid());
System.exit(1);
}
you can use that code, it's work for me!

Is it normal to call two activities from two buttons in sequence

I didn't know how to phrase the question properly so let me explain.
I have noticed that on the android platform that when you press two buttons in one activity in quick sequence (press one button then the other before the activity has a chance to leave the screen) that two activities are called one after another. It is not visible while it happens but if you press the back button then the activity that was called with the second button leaves (finishes) and the activity that was called with the first button shows up. You have to go back again to go back to the calling Activity. So you have to press back twice to get to Activity 2's parent activity.
So I want to know if this is a problem for others and if so how would you go about fixing that. Or do you think this is not much of a problem.

You can call finish() after startActivity(your_intent); that way the activity you are leaving finishes and you get to the next one, so you dont have to press back twice to get to it's parent Activity.

I have figured out how to pass this problem. I have a base activity class that every other activity in my application inherits from. I override
onResume with:
#Override
protected void onResume()
{
super.onResume();
setCanStartNewActivity(true);
}
and startActivityForResult with:
#Override
public void startActivityForResult(Intent intent, int requestCode)
{
//Does not allow starting a new activity unless previous activity returned
//This is a trick to stop multiple simultaneous button presses starting multiple
//activities simultaneously.
if(!canStartNewActivity)
return;
setCanStartNewActivity(false);
super.startActivityForResult(intent, requestCode);
}
This basically makes sure only one new activity can be started for a button press. If you let go of two buttons at the same time only the button released the earliest (even by 10 microseconds) will be fired and the other will still send the intent but it will not fire until the first fired activity returns or the app dies.