Is that logical and a right way to add a button to close application in java?

Question

I'm using Android Studio. In the MainActivity inside the onCreate I did:

@Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);        
        startTime = SystemClock.uptimeMillis();
        serverChecksThread.start();
        status1 = (TextView) findViewById(R.id.textView3);
        timerValue = (TextView) findViewById(R.id.timerValue);
        uploadedfilescount = (TextView) findViewById(R.id.numberofuploadedFiles);
        uploadedfilescount.setText("Uploaded Files: 0");

        addListenerOnButton();
        initTTS();

        Button btn1 = (Button) findViewById(R.id.btn1);
        btn1.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                finish();
                System.exit(0);
            }
        });
    }

And in the activity_main.xml I added:

<Button android:layout_width="fill_parent"
            android:layout_height="wrap_content" android:id="@+id/btn1"
            android:text="Close App" />

I have two questions.

The main is that if it's logical and good thing to do to add a button that will close the application so it will not leave anything behind? This way when i'm running the application over again on my android device it's starting clean reseted.

The sub question is when I click the button and exit the app then when I'm running it again for a millisecond the app blink. And it happen after I added this button code it wasn't before. I'm not getting error or exception but it's blinking for a very short time.

Answer 1

"Running" and "closed" are fuzzy concepts in Android. When an app is in the background, it may or may not actually be running. When an activity is in the backstack, an in-memory instance of it may or may not exist. When your last activity finishes, the framework may or may not kill the process. And when you start the app again, the framework may or may not create a new instance of your Application class.

Calling System.exit(0) is a bad idea because it short-circuits the Android framework. It may result in unspecified behavior (read: really strange bugs.) Better to just finish your last activity and let the framework do as it likes.

Whether it's good UX to show a close button is a matter of opinion. Google recommends against it. The preferred way to "close" an activity is by pressing the back button.

Answer 2

It is not necessary that you add a close button to an application on android because, there is usually a, either software button, or b, a hardware button on the device to close (minimize) applications. so it wouldn't be a good thing to add a button, and it would also be illogical

And for your second question, I did not quite understand your point.

Answer 3

Even if you close your app with a button, it won't be closed permanently, it still will be shown on the users device as a 'running on background app'. Because android is not working like windows, so its not so useful to add such a button. As far as i know the only apps that using this button is using it to be sure in 100% that the user left the app and that the connection that he had will be closed, so no one else will be able to use his login or password...