Develop Reference

Android phone built-in back button

I have an activity with two fragments, each fragment has a back button to the previous activity/fragment. Both the back buttons on the fragments work properly. However when i run the app on my android phone and i use the built-in back button to navigate to the previous activity, it displays a blank activity and then when i press the built-in back button again only then does it navigate to the previous activity. The problem is clearly the back burton than built in.Is there a way to solve this???

There is a method in the Activity called onBackPressed() which is called when the device back button is pressed. If you want to control what happens on back press just override it. To remove default onBackPressed action you need to remove the call to super.onBackPressed() and then you control what happens when back button is pressed.
#Override
public void onBackPressed() {
//super.onBackPressed();
// do something here
// or perhaps nothing at all
}

Android back button in device

I have Activity A (Main) and Activity B.
From A, I can go to B. When I test I do the next:
Go from A (a1) to B (b1). Then go back to A (a1). The again from A (a1) to B (b2) and go back to A (a1).
If I push the back button again after doing what I said, I want to exit the app but it returns to the first instance of B (b1), and then if I push again, it goes to the first instance of A(a1) and if a push again now it exit the app.
I don't want this behavior, if I am in activity A and push back button I want to exit the app, not to go to every instance of activities until goes to the first one and then exit.
I hope I was clear.

Probably what you are doing is to stack one Activity in top of the other.
You can make sure to close B activity if you implement the onBackPressed() function and finish the activity like this:
#Override
public void onBackPressed() {
finish();
}
This way you'll return to your original A activity (and not another instance -- like A1), and if you try to go back from A you'll exit the app.
I hope it helps!

BackButton takes me to home, but return to wrong activity

I have an android app with a loginActivity and then MainActivity.
The startpoint is the loginActivity, when you first open the app you log in and then it starts the MainActivity.
I overrided onBackPressed from the MainActivity so you wont get back to loginActivity, unless you tap a logout button.
#Override
public void onBackPressed() {
Intent mainActivity = new Intent(Intent.ACTION_MAIN);
mainActivity.addCategory(Intent.CATEGORY_HOME);
mainActivity.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(mainActivity);
finish();
}
The problem is, when i press back button, it shows the home luncher (as expected) but when i open the app again, it goes to loginActivity.
Is there any way to "bypass" the loginActivity or to tell android in which activity i stay last time?

I would set a preference if the user already logged in. In the LoginActivity's onCreate you can check the preference and start HomeActivity if needed + call finish() in LoginActivity. This way you don't even have to override onBackPressed later and everything will just work.

I would suggest changing the entry point of your application to the MainActivity, doing a check within that activity to see if the user is logged in, and redirect to the login activity if they are not logged in.

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!

block back button for ceratin activities

I have two activities A and B. What I want is to show activity A as an intro, the user will be unable to navigate back to it. Is there some flag I can set to activity A to do this? Can I block the back button for one activity only? Activity A is of course my main activity which automatically starts activity B after some "hard work".
Best regards.

you do not need to block the back button, but just call finish() on your A activity after firing an intent to start B. Back button pops the previous activity from activity stack and it won't be able to pop A if it is already finished.

For this you don't need to block the Back button. Simply, start the second Activity and quit the first one. And now if user presses the Back, they will be taken to the Android home screen not on your apps home screen.
Updates: By the way if you want to intercept the Back button for any reason, simply override the onBackPressed() method of Activity class. See this for details.

Never override the functionality of a hardware button.
You should call finish() in Activity A right after starting Activity B (calling the Intent).

it works but the application terminates and i'm redirected to android's applications screen. I would like to stay in activity B if back button is pressed, i don't want to exit the app. here's is what i got :
public void startProgram(Context context){
Intent intent = new Intent(context, ActivityB.class);
startActivity(intent);
finish();
}