使用LiveData处理事件

package com.example.android.architecture.blueprints.todoapp;
 
import android.arch.lifecycle.LifecycleOwner;
import android.arch.lifecycle.MutableLiveData;
import android.arch.lifecycle.Observer;
import android.support.annotation.MainThread;
import android.support.annotation.Nullable;
import android.util.Log;
 
import java.util.concurrent.atomic.AtomicBoolean;
 
/**
 * A lifecycle-aware observable that sends only new updates after subscription, used for events like
 * navigation and Snackbar messages.
 * <p>
 * This avoids a common problem with events: on configuration change (like rotation) an update
 * can be emitted if the observer is active. This LiveData only calls the observable if there‘s an
 * explicit call to setValue() or call().
 * <p>
 * Note that only one observer is going to be notified of changes.
 */
public class SingleLiveEvent<T> extends MutableLiveData<T> {
 
    private static final String TAG = "SingleLiveEvent";
 
    private final AtomicBoolean mPending = new AtomicBoolean(false);
 
    @MainThread
    public void observe(LifecycleOwner owner, final Observer<T> observer) {
 
        if (hasActiveObservers()) {
            Log.w(TAG, "Multiple observers registered but only one will be notified of changes.");
        }
 
        // Observe the internal MutableLiveData
        super.observe(owner, new Observer<T>() {
            @Override
            public void onChanged(@Nullable T t) {
                if (mPending.compareAndSet(true, false)) {
                    observer.onChanged(t);
                }
            }
        });
    }
 
    @MainThread
    public void setValue(@Nullable T t) {
        mPending.set(true);
        super.setValue(t);
    }
 
    /**
     * Used for cases where T is Void, to make calls cleaner.
     */
    @MainThread
    public void call() {
        setValue(null);
    }
}