CODEWITHSUNDEEP
androidmultithreadingandroid-asynctask
Brian D
Brian D

Reputation: 10133

How to properly use AsyncTask

I want to capture a frame buffer from a camera surface preview and send those buffers to another function to be processed / POSTed somewhere on the web.

The Android Dev guide gives this example: http://developer.android.com/reference/android/os/AsyncTask.html

 private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
     protected Long doInBackground(URL... urls) {
         int count = urls.length;
         long totalSize = 0;
         for (int i = 0; i < count; i++) {
             totalSize += Downloader.downloadFile(urls[i]);
             publishProgress((int) ((i / (float) count) * 100));
         }
         return totalSize;
     }

     protected void onProgressUpdate(Integer... progress) {
         setProgressPercent(progress[0]);
     }

     protected void onPostExecute(Long result) {
         showDialog("Downloaded " + result + " bytes");
     }
}

Here's how you execute it:

new DownloadFilesTask().execute(url1, url2, url3);

Is this entire operation one big AsyncTask (in other words, is that loop going to sit there and wait for each file to download synchronously) while the entire task works in the background, or is this going to start up multiple threads for each URL that was passed?

Related to my project, would it be reasonable to simply create a brand new AsyncTask every single time I want to capture a frame buffer? Something along the lines of:

//for each frame buffer i want to process:
    new FrameProcessorTask().execute(byte[]);

Upvotes: 3

Views: 4687

Answers (2)

mxk
mxk

Reputation: 43524

It will be a single thread, taken from a managed thread pool. The argument ellipsis is simply the input to your doInBackground method. As you can see from the example, no threads are spawned in there. If you want to use one thread per URL, you'll have to create a new AsyncTask for each of them.

Upvotes: 4

Heiko Rupp
Heiko Rupp

Reputation: 30934

It is one thread that is looping over the data.

You can do the latter too.

With the 2nd option, you need to take the heap size into account, as the handset only has a limited amount of memory and many parallel threads, all downloading in big buffers may overrun the available memory.

Upvotes: 3

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