Question

I want to get some data from the network in a while loop until the user clicks a button on the screen, then stop to receive the data and show another activity. What I do to receive is as follows:

Thread listUpdater;

…

listUpdater = new Thread() {
    @Override
    public void run() {
        TimerTask task = new UpdateListTask();

        while (true) {
            task.run();
        }
    }
};
listUpdater.start();

…

public class UpdateListTask extends TimerTask {

     public UpdateListTask() {
     }

     @Override
     public void run() { 
        // get some data from network (asynchronically)
     }
}

Once the user has clicked a button, I run the following code:

try {
    listUpdater.join();
} catch (InterruptedException e) {
    e.printStackTrace();
}

But it doesn’t stop the run loop in the new thread/timer task, all code is still being run – what I don’t want. What can I do to stop the code being run? Is there a way to stop the thread? Or can I do some inter-thread-boolean variable setting to stop the while loop?

I tried everything but didn’t succeed. Can anyone please help?

Answer 1

.join waits until the thread is finished. Your thread will never finish, and so everything breaks.

An easy way to actually stop the thread is this:

volatile boolean updateList;
Thread listUpdater;

…

listUpdater = new Thread() {
    @Override
    public void run() {
        TimerTask task = new UpdateListTask();

        while (updateList) {
            task.run();
        }
    }
};
updateList = true;
listUpdater.start();

and

try {
    updateList = false;
    listUpdater.join();
} catch (InterruptedException e) {
    e.printStackTrace();
}

This way you use the boolean variable as a flag with which to control the execution of your listUpdater thread. Remember to set it back to true every time you want to relaunch the thread.