android-live-data.md

title: Android: Live Data tags: android,android-lifecycle

Live data is a way for you to observe changes to data. Let's use it in a ViewModel:

import android.arch.lifecycle.LiveData;
import android.arch.lifecycle.MutableLiveData;
import android.arch.lifecycle.ViewModel;

public class MyViewModel extends ViewModel {
    public MutableLiveData<String> text = new MutableLiveData<>();

    public LiveData<String> getText() {
        return text;
    }

    public void setText(String text) {
        this.text.setValue(text);
    }
}

Instead of having a plain String we have a MutableLiveData object. And when we want to update data we use setValue.

getText() returns a LiveData object. Let's see how we use that in our activity or fragment:

MyViewModel vm = ViewModelProviders.of(this).get(MyViewModel.class);

vm.getText().observe(this, new Observer<String>() {
    @Override
    public void onChanged(@Nullable String s) {
        ((TextView)findViewById(R.id.aTextView)).setText(s);
    }
});

We observe it. So when it changes we update our view.