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    <p>It appears that for every value change in your slider, you are creating your <code>MyTask</code> and running it. Instead, one thing that might perform better is only updating your listener when the slider has been released (stopped moving). It looks like <code>HorizontalSlider</code> is a custom class, so I can't speak for what is happening in there.</p> <p>If a slider is being moved from left to right, it may fire off update events 100 times during that move. That would be 100 background tasks!</p> <p><strong>UPDATE</strong></p> <p>One possibility would be to <code>cancel()</code> your active <code>MyTask</code> before you produce another one. If you take that route you need to call <code>isCancelled()</code> in <code>onPostExecute</code> and only invalidate your view if the task is <em>not</em> cancelled. However, if the code in <code>findCirclePixels()</code> is the bottleneck, this will not work. My guess is that cancelling the active task before creating a new one will <strong>NOT</strong> solve your problem.</p> <p>Coding this up properly (only creating your <code>MyTask</code> when necessary) is still going to be the best route. Consider that for every <code>AsyncTask</code> the OS has to spawn a new background thread, which comes with its own overhead. Don't be fooled by the small amount of code you have put in <code>doInBackground()</code>.</p> <p><strong>UPDATE AGAIN</strong></p> <p>I have cleaned up your code and added comments for suggestion:</p> <pre><code>public class TouchView extends View{ private File tempFile; private byte[] imageArray; private Bitmap bgr; private Bitmap bm; private Bitmap bgr2 = null;; private Paint pTouch; private int centreX = 1; private int centreY = 1; private int radius = 50; private int Progress = 1; private static final String TAG = "*********TouchView"; private Filters f = null; private MyTask mt = null; public TouchView(Context context) { super(context); } public TouchView(Context context, AttributeSet attr) { super(context,attr); tempFile = new File(Environment.getExternalStorageDirectory(). getAbsolutePath() + "/"+"image.jpg"); imageArray = new byte[(int) tempFile.length()]; try{ InputStream is = new FileInputStream(tempFile); BufferedInputStream bis = new BufferedInputStream(is); DataInputStream dis = new DataInputStream(bis); int i = 0; while (dis.available() &gt; 0) { imageArray[i] = dis.readByte(); i++; } dis.close(); } catch (Exception e) { e.printStackTrace(); } BitmapFactory.Options bfo = new BitmapFactory.Options(); bfo.inSampleSize = 1; bm = BitmapFactory.decodeByteArray(imageArray, 0, imageArray.length, bfo); bgr = Bitmap.createBitmap(bm.getWidth(), bm.getHeight(), bm.getConfig()); bgr = bm.copy(bm.getConfig(), true); bgr2 = Bitmap.createBitmap(bm.getWidth(), bm.getHeight(), bm.getConfig()); f = new Filters(); } public void findCirclePixels(){ float prog = (float) Progress / 150000; bgr2 = f.barrel(bgr, prog); } public void initSlider(final HorizontalSlider slider) { slider.setOnProgressChangeListener(changeListener); } private OnProgressChangeListener changeListener = new OnProgressChangeListener() { @Override public void onProgressChanged(View v, int progress) { /* TODO: If there is a way to see if the slider is still being changed (control has not been released), then you should return and not continue with the creation of another task */ this.Progress = progress2; if (mt != null) { mt.cancel(); } mt = new MyTask(); mt.execute(); } }; private class MyTask extends AsyncTask&lt;Void, Void, Void&gt; { protected void onPreExecute() { } @Override protected Void doInBackground(Void... params) { // This check is not necessary if coded properly if (!isCancelled()) { TouchView.this.findCirclePixels(); } return null; } protected void onPostExecute(Void result) { // This check is not necessary if coded properly if (!isCancelled()) { TouchView.this.invalidate(); } } } @Override public void onDraw(Canvas canvas){ super.onDraw(canvas); canvas.drawBitmap(bgr2, 0, 0, null); canvas.drawCircle(centreX, centreY, radius, pTouch); } } </code></pre>
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    1. COHi, that makes sense. How about cancelling the AsyncTask in onProgressChanged(), then execute AsyncTask in setProgress. That way there'll be only one Asynctask running when the slidebar is moved?
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    2. CO@turtleboy See my update
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    3. COjust updated post. How would you code this up properly? thanks
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