在onChanged（）回调，Livedata中解析不同的对象

Question

I want to listen to value changes in different fields in an activity. So I have implemented the Observer interface, and bind these fields. How do I differentiate which value is changed in onChanged() since there is one callback for both variables or what is the best practice/efficient way (in terms of memory consumption) to parse incoming objects in onChanged() ?

public abstract class BaseActivity extends AppCompatActivity implements Observer {

    public MutableLiveData<Integer> status;
    public MutableLiveData<UserAccount> userAccount;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        status.observe(this, this);
        userAccount.observe(this, this);
    }

    @Override
    public void onChanged(@NonNull Object o) {
        // Best practice to parse/know different object types?
    }
}

Answer 1

You should avoid implementing in this manner since the types (Integer,UserAccount) for the Observer is different.

Since there is not status object indicating which MutableLiveData obj received the value, one work around is to use instanceOf operator in onChanged and check if its Integer or UserAccount .

I would recommend you to avoid this since it would not be a great design and difficult to maintain.

You can make it separation of concern by creating two Observers one with Observer<Integer> and another with Observer<UserAccount> as follows:

class StatusObserver implements Observer<Integer> {
    @Override
    public void onChanged(@NonNull Integer status) {
        // do something
    }
}

class UserAccountObserver implements Observer<UserAccount> {
    @Override
    public void onChanged(@NonNull UserAccount userAccount) {
        // do something
    }
}

This is much cleaner approach, easy to maintain and since you have separated it, changes to handling of status won't impact handling of userAccount.

Alternatively, you can implement them as anonymous classes as follows:

status.observe(this, new Observer<Integer>() {
    @Override
    public void onChanged(@Nullable final Integer integer) {

    }
});