Change a dialog's message while using AsyncTask?

Question

I looked at a few other questions regarding a similar issue, and I figured out that I need to use the onProgressUpdate method to change the message of ProgressDialog.

For example, I have code like this that runs in the AsyncTask's doInBackGround (this is just a very small sample):

        byte[] data = getBytesFromFile(image);

        String lineEnd = "\r\n";
        String twoHyphens = "--";
        String boundary = "*****";
        pictures.dia.setProgress(30);
        pictures.dia.setMessage("Data beginning upload sequence...");

        URL connectURL = new URL(this.base_url);
        HttpURLConnection conn = (HttpURLConnection) connectURL.openConnection();
        conn.setDoInput(true);
        conn.setDoOutput(true);
        conn.setUseCaches(false);
        conn.setRequestMethod("POST");

        conn.setRequestProperty("Connection", "Keep-Alive");
        conn.setRequestProperty("Content-Type", "multipart/form-data, boundary=" + boundary);

        DataOutputStream dos = new DataOutputStream(conn.getOutputStream());
        pictures.dia.setProgress(40);
        pictures.dia.setMessage("Output Stream prepared...");

When I originally run thus, I get a Leaky Window error saying that I can't change dia's message outside of AsyncTask.

So my question is, how do I use onProgressUpdate to set the message of dia when dia's progress reaches a certain number? (i.e., when dia's progress = 30, make it say "Data beginning upload sequence...")
onProgressUpdate must obviously always be checking dia's progress (like a listener, I suppose)[if it doesn't already do this, how can I make it do this?]

Moonlighting

Answer 1

You need to implement the onProgressUpdate method of AsyncTask. Create a new class that holds the progress percentage and the message only to be the onProgressUpdate method's only parameter.

In the onProgressUpdate, call dia.setProgress and dia.setMessage.

In your doInBackground method, call publishProgress with an instance of your new class that contains the new percentage and message. That will cause the AsyncTask to call onProgressUpdate on the main thread.

For example:

private static class TaskProgress {
    final int percentage;
    final String message;

    TaskProgress(int percentage, String message) {
        this.percentage = percentage;
        this.message = message;
    }
}

In your AsyncTask (replace the ?s with the correct types for your implementation):

public ProgressAsyncTask extends AsyncTask<?, TaskProgress, ?> {

    public void onProgressUpdate(TaskProgress progress) {
         pictures.dia.setProgress(progress.percentage);
         pictures.dia.setMessage(progress.message);
    }

    public ? doInBackground(?... params) {
        // ... your code       
        publishProgress(new TaskProgress(30, "A new update"));
        // ... your code 
    }

}

Ineptitude

Okay, I see how this works. I have one problem right now: I'm getting an error when I put publishProgress(new TaskProgress(10, "Beginning sequence...")); in some runnable code. My runnable is called in the doInBackground method, but isn't physically in that method. Also, the runnable later calls another method from another class, where I can't use publishProgress. Any way around this? – Moonlighting

Note: if I try Task.publishProgress(new TaskProgress(10, "My message here..."));, it says that publishProgress is not visible from the AsyncTask. Not sure if that helps or not. – Moonlighting

You have to call publishProgress inside your doInBackground method. – Ineptitude

Thats not the problem. All my doInBackground method is is uploader.run(), where I run my Runnable code that is outside the doInBackground method. Do you see the problem here? doInBackground calls the runnable and nothing more, and I don't want to put the runnable inside doInBackground. – Moonlighting

Answer 2

You're right in that you should put the code for updating the views in dia in the onProgressUpdate method. To ensure that onProgressUpdate is called, though, you need to make calls to publishProgress. Basically, you call publishProgress from your background thread and then the system, at some undefined time in the future, will invoke onProgressUpdate on the UI thread.

Okajima

So instead of pictures.dia.setProgress(some number), I should use publishProgress(some number)? OK, from there though, how does onProgressUpdate display the right message I want? – Moonlighting