Question

I am trying to write a new feature for a flashlight app. I am pretty sure I need a new Thread to do this. HOWEVER, I am new to Threads and do not know how to do it at all. What I am trying to do is on the change of a SeekBar, I want the strobe to get faster/ slower. If it is 0 or 1 resume to constant light.

This is wrong, but this is what I have. Whenever I move the SeekBar it correctly strobes, but you cannot make it stop..

In onCreate():

    mSeekBar.setOnSeekBarChangeListener(new OnSeekBarChangeListener(){
      public void onProgressChanged(SeekBar seekBar, int progress, boolean fromTouch) {
        final int myInt = progress;
        new Thread (new Runnable() {
          public void run() {
            if (myInt>1)
                strobeLight(myInt);
            else {}
                // Stop Strobe
          } }).start();
      }
      public void onStartTrackingTouch(SeekBar seekBar) {}
      public void onStopTrackingTouch(SeekBar seekBar) {}          
    });

strobeLight() method:

public void strobeLight(int myInt){
    do {
    if (myInt>1){
            if (strobe){
                processOffClick();
                try { Thread.sleep(300/myInt); }
                    catch (InterruptedException e) {}
                strobe=false; 
                strobeActivated=true;}
            else{
                processOnClick();   
                try { Thread.sleep(300/myInt); }
                    catch (InterruptedException e) {}                       
                strobe=true; }
        }
    else{
        processOnClick();
        strobe=false; 
        Thread.currentThread().interrupt(); 
        strobeActivated=false;}

    } while (strobeActivated);
} 

Answer 1

I am unsure about the need of creating a new thread every time the progress changes, a better approach might be to create a final runnable in which you change the integer value:

onProgressChange:

    public void onProgressChanged(SeekBar seekBar, int progress, boolean fromTouch) {
        toRun.interval = progress;
    }

A runnable-implementation:

    class StrobeRunnable implements Runnable {
        volatile boolean running;
        volatile int interval = 0;
        private boolean lightIsOn = false;

        @Override
        public void run() {
            while(running){
                if (interval > 1){
                    Thread.sleep(300/interval);
                    lightIsOn = !lightIsOn;
                    switchLight(lightIsOn);
                }
                else{
                    Thread.sleep(600/interval);
                    if( !lightIsOn ){
                        lightIsOn = true;
                        switchLight(lightIsOn);
                    }
                }
            }
        }
    };

Note that I created new names for some methods,
switchLight(boolean isLightOn) is what I believe your processXClick did before, namely switch the light on or of.
And interval used to be called myInt.

To start a thread I prefer to use Executors:

    StrobeRunnable toRun = new StrobeRunnable();
    Executor exec = Executors.newSingleThreadExecutor();
    exec.execute(toRun);

To completely stop the thread from running, set the toRun.running to false, and this will stop the running loop.

I haven’t tested this but it should work. It also depends a bit on how your processClick-method looks.