CODEWITHSUNDEEP
androidmultithreadingbitmaphandler
Learner
Learner

Reputation: 519

How to send a bitmap data to the main thread from a background thread?

I'm creating a face detection app and to decrease the workload on the main thread I'm using a background thread. The code is given below.

Thread background = new Thread(new Runnable() {

    public void run() {

    Log.d ("Thread", "Thread has started");

    for (Feature feat : mClassifierFiles.keySet()) {
        mFaces.put(feat, cvHaarDetectObjects(grayImage,  mClassifiers.get(feat), mStorages.get(feat), 1.1, 3,
                        CV_HAAR_DO_CANNY_PRUNING));

        if (mFaces.get(feat).total() > 0) {

            Size previewSize = camera.getParameters().getPreviewSize(); 
            YuvImage yuvimage=new YuvImage(data, ImageFormat.NV21, previewSize.width, previewSize.height, null);
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            yuvimage.compressToJpeg(new Rect(0, 0, previewSize.width, previewSize.height), 100, baos);
                byte[] jdata = baos.toByteArray();
            Bitmap bmp = BitmapFactory.decodeByteArray(jdata, 0, jdata.length);
            saveImg(bmp);

            }

    postInvalidate();
    opencv_core.cvClearMemStorage(mStorages.get(feat));

    }
     }
 });

 background.start ();

Now, I understand that the saving image part should be done in the main thread. Now what I don't get is, how to send the 'bitmap bmp' to the main thread?

Upvotes: 2

Views: 1415

Answers (2)

Todor K.
Todor K.

Reputation: 651

The recommended way is to use an AsyncTask. It allows you to do some work in a background thread and then get the result on the main thread. Look it up and it will be obvious how to use it.

By the way, I don't see why you should do the saving of the bitmap on the main thread. That's a slow operation and should also be done in the background thread. Only displaying the image (or other UI interactions) should be done the main thread.

Upvotes: 2

type-a1pha
type-a1pha

Reputation: 1893

Either define a BroadcastReceiver and send an Intent from your worker thread, since Bitmap is Parcelable. You can also use startIntent if you want to launch a new activity to handle the bitmap, thus you won't need to define a BroadcastReceiver. Or define an Handler in your main thread, pass it to your worker thread and then post a Runnable to be executed on the main thread. You can also use runOnUiThread().

Upvotes: 1

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