How to stop a thread in Java Android?

Question

This is the code of my testing app:

public class MainActivity extends Activity
{
    private TextView text;
    private Button start;
    private Button stop;
    private TestThread Points;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        text = (TextView) findViewById(R.id.mainTextView1);
        start = (Button) findViewById(R.id.mainButton1);
        stop = (Button) findViewById(R.id.mainButton2);

        Points = new TestThread();

        start.setOnClickListener(new OnClickListener() {
                @Override
                public void onClick(View p1)
                {
                    if (! Points.isAlive())
                    {
                        Points.start();
                    }
                }
        });

        stop.setOnClickListener(new OnClickListener() {
                @Override
                public void onClick(View p1)
                {
                    if (Points.isAlive())
                    {
                        Points.stop();
                    }
                }
            });
    }

    public class TestThread extends Thread
    {
        private String points;

        @Override
        public void run()
        {
            for (int a = 0; a < 3; a++)
            {
                try
                {
                    if (a == 0) points = ".";
                    else if (a == 1) points = "..";
                    else if (a == 2) {
                        points = "...";
                        a = -1;
                    }

                    runOnUiThread(new Runnable()
                        {
                            @Override
                            public void run()
                            {
                                text.setText(points);
                            }
                        });

                    Thread.sleep(350);

                } catch (InterruptedException e) {}
            }
        }
    }
}

When I click on Start button the thread starts successfully but when I click on Stop button the app crashes... How can i stop the thread successfully without force closing?

Thanks a lot

Answer 1

Thread.stop() function is deprecated and should not be used to stop a thread. this is according to the java docs.

a good way to stop a thread is make it exit its run method.

a simple way to achive this is by adding a boolean member to your thread class:

public class TestThread extends Thread
{
    private String points;
    private boolean keepRunning = true;

    public cancel(){
        keepRunning = false;
    }

    @Override
    public void run()
    {
        for (int a = 0; a < 3; a++)
        {
            if(!keepRunning) break;

            try
            {
                if (a == 0) points = ".";
                else if (a == 1) points = "..";
                else if (a == 2) {
                    points = "...";
                    a = -1;
                }

                runOnUiThread(new Runnable()
                    {
                        @Override
                        public void run()
                        {
                            text.setText(points);
                        }
                    });

                Thread.sleep(350);

            } catch (InterruptedException e) {}
        }
    }
}

call the TestThread.cancel() function in your stop button onClick method.

Answer 2

Other than adding a Boolean to stop it I believe you could catch InterruptException and just call Thread.interrupt(); which would exit the loop this ending the thread