How to Handle Back Button in Activity

How to handle back button in activity

You can handle it like this:

for API level 5 and greater

@Override
public void onBackPressed() {
    // your code.
}

older than API 5

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_BACK) {
        // your code
        return true;
    }

    return super.onKeyDown(keyCode, event);
}

Android - Back button in the title bar

There are two simple steps to create a back button in the title bar:

First, make the application icon clickable using the following code in the activity whose title bar you want to have a back button in:

ActionBar actionBar = getActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);

After you have added the above code, you will see a back arrow appear to the left of the application icon.

Second, after you have done the above, you still have to create code that will take advantage of the click event. To do so, be aware that, when you actually click on the application icon, an onOptionsItemSelected method is called. So to go back to the previous activity, add that method to your activity and put Intent code in it that will return you to the previous activity. For example, let's say the activity you are trying to go back to is called MyActivity. To go back to it, write the method as follows:

public boolean onOptionsItemSelected(MenuItem item){
    Intent myIntent = new Intent(getApplicationContext(), MyActivity.class);
    startActivityForResult(myIntent, 0);
    return true;
}

That's it!

(In the Android developers API, it recommends messing around with the manifest and adding stuff like android:parentActivityName. But that doesn't seem to work for me. The above is simpler and more reliable.)

<meta-data
      android:name="android.support.PARENT_ACTIVITY"
      android:value=".MainActivity" />

And in your Activity

getSupportActionBar().setDisplayHomeAsUpEnabled(true);

Handling Back button in Parent Activity

i am assuming you are using ActionBar.

Try adding this in your activity:

 @Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case android.R.id.home:
            onBackPressed();
            return true;
    }
    return false;
}

 @Override
public void onBackPressed() {
    AlertDialog.Builder builder = new AlertDialog.Builder(this);

    builder.setMessage("Do you want to leave? ");
    builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int id) {
            MainActivity.super.onBackPressed();
        }
    });
    builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int id) {
            finish();
        }
    });
    builder.show();
}

Android - How To Override the Back button so it doesn't Finish() my Activity?

Remove your key listener or return true when you have KEY_BACK.

You just need the following to catch the back key (Make sure not to call super in onBackPressed()).

Also, if you plan on having a service run in the background, make sure to look at startForeground() and make sure to have an ongoing notification or else Android will kill your service if it needs to free memory.

@Override
public void onBackPressed() {
   Log.d("CDA", "onBackPressed Called");
   Intent setIntent = new Intent(Intent.ACTION_MAIN);
   setIntent.addCategory(Intent.CATEGORY_HOME);
   setIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
   startActivity(setIntent);
}

Handling back button in Android Navigation Component

Newest Update - April 25th, 2019

New release androidx.activity ver. 1.0.0-alpha07 brings some changes

More explanations in android official guide: Provide custom back navigation

Example:

public class MyFragment extends Fragment {

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // This callback will only be called when MyFragment is at least Started.
        OnBackPressedCallback callback = new OnBackPressedCallback(true /* enabled by default */) {
            @Override
            public void handleOnBackPressed() {
                // Handle the back button event
            }
        };
        requireActivity().getOnBackPressedDispatcher().addCallback(this, callback);

        // The callback can be enabled or disabled here or in handleOnBackPressed()
    }
    ...
}

Old Updates

UPD: April 3rd, 2019

Now its simplified. More info here

Example:

requireActivity().getOnBackPressedDispatcher().addCallback(getViewLifecycleOwner(), this);

@Override
public boolean handleOnBackPressed() {
    //Do your job here
    //use next line if you just need navigate up
    //NavHostFragment.findNavController(this).navigateUp(); 
    //Log.e(getClass().getSimpleName(), "handleOnBackPressed");
    return true;
    }

Deprecated (since Version 1.0.0-alpha06
April 3rd, 2019) :

Since this, it can be implemented just using JetPack implementation OnBackPressedCallback in your fragment
and add it to activity:
getActivity().addOnBackPressedCallback(getViewLifecycleOwner(),this);

Your fragment should looks like this:

public MyFragment extends Fragment implements OnBackPressedCallback {

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        
        getActivity().addOnBackPressedCallback(getViewLifecycleOwner(),this);
}
    
    @Override
    public boolean handleOnBackPressed() {
        //Do your job here
        //use next line if you just need navigate up
        //NavHostFragment.findNavController(this).navigateUp(); 
        //Log.e(getClass().getSimpleName(), "handleOnBackPressed");
        return true;
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        getActivity().removeOnBackPressedCallback(this);
    }
}

UPD:
Your activity should extends AppCompatActivityor FragmentActivity and in Gradle file:

 implementation 'androidx.appcompat:appcompat:{lastVersion}'

App closed when pressing back button from activity results intent

After a lot of struggle I found that if we press back button with out selecting any file the activity results will returns null.
So we should check if activity results not equal to null and then do some operations.

ActivityResultLauncher<String> mGetContent = registerForActivityResult(new GetContent(),
    new ActivityResultCallback<Uri>() {
        @Override
        public void onActivityResult(Uri uri) {
           if(uri!=null){
            // Handle the returned Uri
           }
        }
});

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