缩放位图并上传到服务器，ui线程阻塞

Question

I'm working on an Android app where I need to upload an image to a server.

Before I upload the image, I'm scaling it to a max width/height of 500 with Bitmap.createScaledBitmap()

The problem I have is that the UI thread get's stuck even though I do both steps in a background thread.

My code looks like this:

dialog = ProgressDialog.show(this, "", "Loading...", true);
// upload the image to the server
Thread t = new Thread() {
    @Override
    public void run() {
        bmp = BitmapHelper.scaleBmp(bmp, 500);//bmp is a private class Bitmap
        try {
            HttpResponse response = Helper.uploadBitmap(bmp);
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                response.getEntity().getContent(), "UTF-8"));
            StringBuilder builder = new StringBuilder();
            for (String line = null; (line = reader.readLine()) != null;) {
                builder.append(line).append("\n");
            }
            finalResult = new JSONObject(builder.toString());
        } catch (Exception e) {
            e.printStackTrace();
        }
        handler.post(new Runnable() {
            @Override
            public void run() {
                handleData();
            }
        });
    }
};
t.run();

Any help on how to do this correctly would be really appreciated!

EDIT: adding handleData() function

public void handleData() {
    take.setVisibility(View.VISIBLE);
    select.setVisibility(View.VISIBLE);

    process.setVisibility(View.GONE);
    select_new.setVisibility(View.GONE);

    message = "An error occured! Please try again.";
    boolean success = false;
    try {
        success = finalResult.getBoolean("success");
        url = "http://url";
        url += finalResult.getString("path");
        thumbnail = finalResult.getString("thumbnail");
    } catch (Exception e) {
        e.printStackTrace();
        Log.e(TAG, e.getMessage());
    }
    if (success) {
        message = "Picture was uploaded successfuly!";
    }
    dialog.dismiss();
    Config.toast(this, message);

    Thread t = new Thread() {
        @Override
        public void run() {
            final Bitmap b = HttpHelper.getBitmapFromURL(thumbnail);
            preview_image.post(new Runnable() {
                @Override
                public void run() {
                    preview_image.setImageBitmap(b);
                    preview_image.setVisibility(View.VISIBLE);
                    preview_image.setOnClickListener(context);
                }
            });
        }
    };
    t.run();
}

Answer 1

I think the problem is you are starting a new thread and then inside of it you're using Handler to post another runnable . So, the Handler is associated with this new Thread and you cannot manipulate the UI thread from that thread . It seems to me that you really should be using an AsyncTask , which provides a convenience for switching from background threads to the UI thread very easily.

http://developer.android.com/reference/android/os/AsyncTask.html

Answer 2

You are not starting new threads. You are creating thread objects but you never start new threads. Instead, you just execute the method run in the current thread. For reference how to start a new thread see Defining and Starting a Thread .

As @LuxuryMode says, AsyncTask is a very good alternative on Android for long running operations that should not block the ui thread.

Answer 3

除了其他发布者所说的以外，运行线程是通过调用start（）而不是run（）来完成的。