完成Android中的父级和当前活动

Question

I have 3 activities. Activity A which leads to activity B, which in turn can go back to activity A or start activity C. However, if I press back in activity C the app should close.

To sum up:

• Activity A starts activity B
• Pressing Back on activity B should lead to A
• Activity B starts activity C
• Pressing Back on activity C should close the app

How should I go from activity B to C? This code currently gives me a NullPointerException on the last line:

Intent intent=new Intent(ActivityB.this, ActivityC.class);
startActivity(intent);
ActivityB.this.finish();
ActivityB.this.getParent().finish();

If I switch the last two lines I also get a null pointer.

Answer 1

I don't know if this will work, but you could try it:

• From Activity A, start activity B for a result using startActivityForResult()

• In Activity B, when the user triggers Activity C, start activity C.

startActivity() returns immediately, so

• set a result that will inform A to finish as well,

• Call finish() in B.

• When A receives that result from B, A calls finish() on itself as well.

Failing that, you could make Activity C into its own app and then close the first app (with A & B) after it starts the second.

PS Take Falmarri's comment into consideration as you move forward!
Good luck.

Answer 2

If you want to finish a parent activity from a child activity,

In the parent activity, while triggering the child activity, use the following command:-

startActivityForResult(intent_name,any_integer_variable);

and override the onActivityResult Method in the following manner:-

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if(resultCode==2){
        finish();
    }
}

Now, in the child activity, override onStop and onDestroy in the following manner:-

protected void onStop() {
    setResult(2);
    super.onStop();
}
@Override
protected void onDestroy() {
    setResult(2);
    super.onDestroy();
}

Notice that I've set the value to 2 in the child activity, and am checking for it in the parent activity. If the value is the same that I have set, then the parent activity will also finish. Then you can use recursive approaches for further activities.

Answer 3

You shou use onActivityResult method in your parent Activity

Suppose Activity A is parent of Activity B. If you want to click back button in Activity B to exit Application (also exit Activity A)

In your Activity B, in onStop() or onDestroy()

you call

setResult(0); //any int number is fine

this will pass a result code to its parent activity.

Your parent Actvity A, listens for the result code you will need to use onActivityResult method inside the method you can call

if(resultCode == 0) //matches the result code passed from B
{
    ActivityA.this.finish()
}

It works for me :)

Answer 4

I didn't do any of this. This is how I would revise your code.

the code you use to enter another intent:

Intent whatEverIntentName = new Intent("Path.to.next.Intent");
startActivity(whatEverIntentName);
finish();

This way, you always quit when pressing back. But wait! You can change how you want your back key press to react when pressed.

Do this:

@Override
public void onBackPressed() {
    super.onBackPressed();
    Intent whatEverIntentName = new Intent("Path.to.the.activity.before.it");
    startActivity(whatEverIntentName);
// Don't add finish here. 
//This is necessary because you finished your last activity with finish();
}

Answer 5

None of that worked for me. So I found out a solution. The help clearly lists that Intent.FLAG_ACTIVITY_CLEAR_TASK must be used with Intent.FLAG_ACTIVITY_NEW_TASK. So here is a code that worked for me.

Intent intent=new Intent(ActivityB.this, ActivityC.class);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK|Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);

Answer 6

try this

  Intent intent = new Intent(Intent.ACTION_MAIN);
  intent.addCategory(Intent.CATEGORY_HOME);
  intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
  startActivity(intent);                

Answer 7

if you are on Activity A and started another activity called Activity B. Activity A --> Activity B

And now want to close both activities.

then use the below code in Activity B.

B.this.finish();

And use this code in Activity A:

startActivity(new Intent(A.this, B.class));
finish();

As soon as activity B will finish, Activity A will also finish.

There is one drawback, I do not know may be you want this or not.

Drawback is that If user is on Activity B and s/he press back button to move on the Activity A. Then, Activity A will also finish in this case.

Answer 8

Intent intent=new Intent(ActivityB.this, ActivityC.class);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
startActivity(intent);

your activity C will the root activity and on press back will finish the apps.

Answer 9

From the screen(B) you want to start the screen(C) with NO back screen, just start this screen (C) with:

screenC.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP 
    | Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_SINGLE_TOP);
startActivity(screenC);
finish();

The back in screenC will exit the application.

Answer 10

From Activity A, start activity B for a result using startActivityForResult(intent,19)

In Activity B, when the user triggers Activity C, start activity C.

startActivity() returns immediately, so

set a result that will inform A to finish as well,

Call finish() in B. and Call setResult() method before finish() method in your Child Activity In Parent Activity overide onActivtyResult(....) method. When A receives that result from B, A calls finish() on itself as well.

enter code here
     @Override
protected void onActivityResult(int arg0, int arg1, Intent arg2) {
    //Added by Ashish to close parent activity
      if(arg1==19){
      finish();
        }
    super.onActivityResult(arg0, arg1, arg2);
}

Answer 11

You can use finishAffinity() , it will close Current & all Parent Activities of the Current Activity.

Note : But any results from Child Activity to Parent Activity will not be handled.

Hope, it helps !!

Answer 12

This is working perfectly:

btn_back.setOnClickListener(new View.OnClickListener()
{
public void onClick(View v) {

Player.this.finish();
    }
});

Answer 13

You can just override the back key behavior :

Activity A starts activity B
Pressing Back on activity B should lead to A
Activity B starts activity C
Pressing Back on activity C should close the app

Note that I don't call super from onBackPressed. This also allows you to override the browse stack mechanism for Android, which I find to be a big advantage, since currently there doesn't seem to be a way to clear the single oldest item from the browse stack in a simple way.

public class B extends Activity
{
    ...
    @Override
    public void onBackPressed()
    {
        // Start activity A
        Intent aIntent = new Intent(this, A);
        startActivity(bIntent);
    }
    ...
}

public class C extends Activity
{
    ...
    @Override
    public void onBackPressed()
    {
        // Close
        finish();
    }
    ...
}

You can specifically finish the parent activity if needed too, but using this method, you don't have to worry about it.

Answer 14

The following code should do it for you. Almost in all other approaches your app will remain in recent apps. Javadoc can be found at, https://developer.android.com/reference/android/app/ActivityManager.AppTask.html#finishAndRemoveTask()

            ActivityManager am = (ActivityManager)getSystemService(Context.ACTIVITY_SERVICE);
            if(am != null) {
                List<ActivityManager.AppTask> tasks = am.getAppTasks();
                if (tasks != null) {
                    tasks.get(0).finishAndRemoveTask();
                }
            }

Answer 15

Have each activity listen for a result from the next activity, and finish itself if that occurs.

You can use a special result code to indicate that you want the activity to finish.