How to kill a process?

Question

I have two activities, the first activity is launched by the Launcher, the second is started by the first. When I kill the process from within the first acitivity, the process gets killed. But when I kill it from within the second activity, the system would immediately launch a new process and the first activity. (The process's PID changed.) How can I do it cleanly?

I tried 3 different ways to kill the process: System.exit(0), android.os.Process.killProcess(pid), and non-programmatically from Eclipse's Devices panel.

Following are two world's most simple acitvities that I experiemented with. They both are outer classes in their respective files.

public class FirstActivity extends Activity  {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        ((Button)findViewById(R.id.button)).setOnClickListener(
            new OnClickListener() {
                public void onClick(View v) {
                    startActivity(new Intent(FirstActivity.this, 
                        SecondActivity.class));
        }});
    }
}

public class SecondActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_2);
        ((Button)findViewById(R.id.button)).setOnClickListener( 
            new OnClickListener() {
                public void onClick(View v) {
                    // Method 1
                    int pid = android.os.Process.myPid();
                    android.os.Process.killProcess(pid);
                    // Method 2
                    System.exit(0);
        }});
    }
}

(I know people say one should never provide a UI to exit the program. But this is for security reason. The user must have a way to exit the program and close the file so that his information won't be leaked.)

consider starting the second activity with startActivityForResult then pass a message from the second activity back to the first using setResult and finish(). Then capture the message in onActivityResult. Switch on the message and call finish? if necessary on the first activity. — JAL

Chris Stratton Chris Stratton · Accepted Answer · 2011-05-07T18:44:32

You can try this.finish()

The other choices kill the process without informing the android system, which assumes something the user wanted to do has crashed and restarts it.

But your assumptions about closing the activity preventing data leakage is mistaken. If you want to provide a log out button, do that and have it negate whatever access tokens/keys were being used to obtain access.

Also think about what happens if some other activity comes to the foreground without the user exiting yours - for example, what if they receive a phone call?

How to kill a process?

4 Answers