observer pattern in Android

Question

I have a problem. 1. I have two threads 'worker' and 'UI' thread. 2. worker keep on waiting for data from server, when gets it notifies to UI thread. 3. On update UI Toast a msg on screen. Step 3 is problem as it says

android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

using mHandler, runOnUIThread slows down the UI thread (UI displays webview), as I have to continuously check for data from server.

Thanks in advance.

Answer 1

Use AsyncTask to implement this. Override doInBackground to get the data (it is executed on the separate thread), then override onPostExecute() to show the toast (it is executed on the UI thread).

Here is good example http://www.screaming-penguin.com/node/7746

And here is javadoc http://developer.android.com/intl/zh-TW/reference/android/os/AsyncTask.html

UPD: Example on how to handle partial progress.

    class ExampleTask extends AsyncTask<String, String, String>{

    @Override
    protected String doInBackground(String... params) {
        while(true){
            //Some logic on data recieve..
            this.publishProgress("Some progress");
            //seee if need to stop the thread.
            boolean stop = true;
            if(stop){
                break;
            }
        }
        return "Result";
    }

    @Override
    protected void onProgressUpdate(String... values) {
        super.onProgressUpdate(values);
        //UI tasks on particular progress...
    }
}

Answer 2

I would use a service, and bind your activity to the service. Then the service can send a broadcast when it has new data