How to update UI elements from a background thread in Android?

Question

I implemented a custom Android camera using the camera2 api and when I click capture button I save the captured image to my phone eternal storage.

Now I needed to show a popup to enter the picture name before saving it and this popup has an imageView to show the captured image.

Even though I am loading the image from the Main thread I am getting this error

  "Only the original thread that created a view hierarchy can touch its views"

Here is the code

  private void initPopup(final Bitmap bitmap) {

    popAddName = new Dialog(this);
    popAddName.setContentView(R.layout.popup_add_name);
    popAddName.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
    popAddName.getWindow().setLayout(Toolbar.LayoutParams.MATCH_PARENT, Toolbar.LayoutParams.WRAP_CONTENT);
    popAddName.getWindow().getAttributes().gravity = Gravity.TOP;

    popup_add = popAddName.findViewById(R.id.popup_add);
    popup_img = popAddName.findViewById(R.id.popup_img);
    popup_name = popAddName.findViewById(R.id.popup_name);

    Thread thread = new Thread() {
        @Override
        public void run() {
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    Picasso.with(getApplicationContext()).load(getImageUri(getApplicationContext(), bitmap)).placeholder(R.drawable.placeholder).into(popup_img);
                }
            });

        }
    };
    thread.start();
}

Here is the method to convert Bitmap to Uri for Picasso loading

  public Uri getImageUri(Context inContext, Bitmap inImage) {
    ByteArrayOutputStream bytes = new ByteArrayOutputStream();
    inImage.compress(Bitmap.CompressFormat.JPEG, 100, bytes);
    String path = MediaStore.Images.Media.insertImage(inContext.getContentResolver(), inImage, "Title", null);
    return Uri.parse(path);
}

This is the capture method

    ImageReader.OnImageAvailableListener readerListener = new ImageReader.OnImageAvailableListener() {
            @Override
            public void onImageAvailable(ImageReader imageReader) {
                Image image = null;
                try {
                    image = reader.acquireLatestImage();
                    ByteBuffer buffer = image.getPlanes()[0].getBuffer();
                    byte[] bytes = new byte[buffer.capacity()];
                    buffer.get(bytes);
                    //CONVERTION BYTES[] TO BITMAP
                    Bitmap bitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.length);

                    //create a new folder in external storage directory
                    String lorealFolder = "coffretPics";
                    File f = new File(Environment.getExternalStorageDirectory(), lorealFolder);
                    if (!f.exists()) {
                        f.mkdirs();
                    }

                    initPopup(bitmap);
                    popAddName.show();

                    file = new File(Environment.getExternalStorageDirectory() + "/" + lorealFolder + "/" + UUID.randomUUID().toString() + ".jpg");


                    save(bytes);


                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    {
                        if (image != null)
                            image.close();
                    }
                }
            }

            private void save(byte[] bytes) throws IOException {
               /* OutputStream outputStream = null;
                try {
                    outputStream = new FileOutputStream(file);
                    outputStream.write(bytes);
                } finally {
                    if (outputStream != null) {
                        outputStream.close();
                    }
                }*/
            }
        };

Can someone please tell me what's the problem ?

Answer 1

Updated answer:

Create a class called AppExecutors

public class AppExecutors {
    // For Singleton instantiation
    private static final Object LOCK = new Object();
    private static AppExecutors sInstance;
    private final Executor diskIO;
    private final Executor mainThread;
    private final Executor networkIO;

    private AppExecutors(Executor diskIO, Executor networkIO, Executor mainThread) {
        this.diskIO = diskIO;
        this.networkIO = networkIO;
        this.mainThread = mainThread;
    }

    public static AppExecutors getInstance() {
        if (sInstance == null) {
            synchronized (LOCK) {
                sInstance = new AppExecutors(Executors.newSingleThreadExecutor(),
                        Executors.newFixedThreadPool(3),
                        new MainThreadExecutor());
            }
        }
        return sInstance;
    }

    public Executor diskIO() {
        return diskIO;
    }

    public Executor mainThread() {
        return mainThread;
    }

    public Executor networkIO() {
        return networkIO;
    }

    private static class MainThreadExecutor implements Executor {
        private Handler mainThreadHandler = new Handler(Looper.getMainLooper());

        @Override
        public void execute(@NonNull Runnable command) {
            mainThreadHandler.post(command);
        }
    }

And get the main thread like:

        AppExecutors.getInstance().mainThread().execute(new Runnable() {
        @Override
        public void run() {
            // Do the work on UI thread here.
        }
    });

That should fix your problem.