Android 使用数据库值更新应用程序视图

Question

So I am currently in the early stages of writing an Android app in Java, using Android Studio. I have the MainActivity, which consists of a TextView and a Button.

The idea is that when I press the button, an entity-objekt is fetched from a Room-Database, a String-Member is extracted from the object and then used to set the new text for the TextView. I would preferably do this in such a way that by pressing the button a new object is fetched from the database and the TextView is updated, all without having to start a new Activity.

The onClick-Method for the button looked something like this in its first version:

private void getFoo() {
    Foo foo = db.fooDao().getRandom();
    String fooName = foo.getFooName();
    textFoo.setText(fooName);
}

The first problem was that I tried fetching the object from database as is, in the main thread, which the compiler was not happy about. Tried to wrap the database interaction into a seperate thread, but then I either had to figure out how to make the value fetched inside the thread to be available outside of it OR I had to nest a call to runOnUiThread in my Thread run() method.

I've had mixed results, with one configuration you could see the new text be displayed on screen, and a split-second after that the app crashed.

Can I make this work as an update of my view within the same Activity or should I instead just start a new one?

Answer 1

Okay I have overlooked a different SO question that perfectly solved my problem. My code for my getFoo now basically looks like this and fulfils the intended function:

private void getFoo() {
    class LoadFooTask extends AsyncTask<Void, Void, Foo> {
        @Override
        protected Foo doInBackground(Void... voids) {
            return db.fooDao().getRandom();
        }

        @Override
        protected void onPostExecute(Foo foo) {
            String FooName = foo.getFooName();
            textFoo.setText(fooName);
        }
    }
    LoadDishTask loadDishTask = new LoadDishTask();
    loadDishTask.execute();
}

The asynchronous task of loading from the database is done inside the doInBackground() method and the UI update is done on the main thread via the onPostExecute() method.