CODEWITHSUNDEEP
androidwhile-loop
Kevin Zhou
Kevin Zhou

Reputation: 1283

possible while loop implementation in android

In my android app, let's say I have 2 buttons, the first button will start the while loop and the second will stop it, and a method do_something() that I will need to execute over and over again continuously.

public void onCreate() {
        my_var = true;
        ok = (Button)findViewById(R.id.button1);
        ok.setOnTouchListener(new OnTouchListener() {

            @Override
            public boolean onTouch(View v, MotionEvent event) {


                if (event.getAction() == MotionEvent.ACTION_DOWN) {
                    while(my_var) do_something();
                }

                return true;
            }
        });

        stop = (Button)findViewById(R.id.button2);
        stop.setOnTouchListener(new OnTouchListener() {

            @Override
            public boolean onTouch(View v, MotionEvent event) {


                if (event.getAction() == MotionEvent.ACTION_DOWN) {
                    my_var = false;
                }

                return true;
            }
        });

the following is causing my application and my entire phone to just freeze up. Can anyone at a glance tell what I am doing incorrectly? aLogCat isn't giving me much info. Any help would be much appreciated!

Upvotes: 0

Views: 1938

Answers (4)

NguyenDat
NguyenDat

Reputation: 4159

To avoid freeze UI thread you can implement while in Thread like this [Ref.1]:

public class MyThread extends Thread {
   private volatile boolean m_bIsRunning= true;

   public void stop() {
      bIsRunning= false;
   }

   public void run() {
      while (bIsRunning) {
         do_something()
      }    
   }
}

References: this

Upvotes: 2

Qasim
Qasim

Reputation: 1704

You can't loop on the UI thread because it doesnt proccess events. Something you can do is make another intent service to do what you want.

Also, instead of using onTouch listeners, you could clean up your code and use this attribute on your button:

android:onClick="onOkTouch"

and then in your activity, have this:

public void onOkTouch(View v, MotionEvent event){
    ...
}

Upvotes: 2

Alex Gitelman
Alex Gitelman

Reputation: 24722

It freezes because the loop executes on UI thread and UI can't process events to stop it. Consequently, it can't be stopped. You must use different thread for such occasion.

Upvotes: 3

Chris Stratton
Chris Stratton

Reputation: 40347

You can't do continued processing on the UI thread, because android can't make any new calls into the UI thread to deliver more messages until the current method returns.

In this case, the exit of your while loop would only occur is response to a new UI event which can't be delivered until you've concluded the while loop and returned.

Upvotes: 3

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