Multiple UI Threads with one Working Thread

Question

I have an app with following Diagram:

Start Screen -> Control Screen <-> Settings Screen <-> Message Screen

The Working-Thread that always have to run is a HTTP Request which gathers Information constantly so it is started at Start Screen.

The Start Screen jumps into Control Screen.

The Information gathered in Working-Thread have to be passed to the Message Screen and being displayed all, even if I change to Settings or Control Screen. Is this made by running 2 UI Threads simultaneausly to update the Message Screen in the background? (I first throught about What's app where the Messages are constantly displayed)

so the information gathered have to be stored in a class and then printed at once in the Message Screen when I start Message Screen Activity? — ionman, Jul 13 '16 at 12:42

score 1 · Accepted Answer · answered Jul 13 '16 at 12:37

1

There is usually only 1 UI thread. If you want to have longer running tasks (especially if you want them to keep going regardless of the UI) then you should use a service. The service can to it's work in the background even when the app is closed. This way you can have one class responsible for all of your network traffic and data collection and all of your activities can just bind to that.

answered Jul 13 '16 at 12:37

CaseyB

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I informed myself about services now and it is what I searched for! Thanks for the hint! (even if its a bit tricky with the binder ;) ) – ionman Jul 13 '16 at 18:18

score 1 · Answer 2 · edited May 23 '17 at 12:14

First of all, there is only ONE UI Thread, and it is the main thread that runs the application, looking at this answer will help you understand Threads in android much better:

The UIThread is the main thread of execution for your application. This is where most of your application code is run. All of your application components (Activities, Services, ContentProviders, BroadcastReceivers) are created in this thread, and any system calls to those components are performed in this thread.

Now, you want to perform actions that require access to the UI Thread(e.g. displaying something on the screen, animating a view, ...etc), So, you have more than an option to achieve that:

1- use the method runOnUIThread():

This method uses the current Activity context or the application context in order to run the wrapped-in-it code inside the UI thread(main thread), only you have to use its signature anywhere in the running activity:

runOnUiThread(new Runnable() {
    @Override
    public void run() {
        mInfo.setText(str);
    }
});

or even you can run it from outside the current activity by holding the activity or the application context anywhere and hence you will be able to run it even from a normal class:

MainActivity.mContext.runOnUiThread(new Runnable() {
    @Override
    public void run() {
        mInfo.setText(str);
    }
});

2- use AsyncTask:

AsyncTask is the android way to do a background work in a background thread then apply the result to the main thread(UI Thread).

All you have to do is use the method doInBackground() provided by AsyncTask in order to handle background work that has to be done in a worker thread(like handling HTTP requests in your case), and then use the method postExecute() in order to reflect the result to the UI Thread:

private class LongOperation extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... params) {
        // handle your worker thread work here
        return "result";
    }

    @Override
    protected void onPostExecute(String result) {
        // update your UI here
    }

}

have a look here to put your hands better on it.

I haven't known the onPostExecute stuff, I update the UI in runonUIThread() Method. Thanks! I already use AsyncTask and doInBackground but a Service fits it better it seems. Even if more complicated. — ionman, Jul 13 '16 at 18:16

Multiple UI Threads with one Working Thread

2 Answers2