RangerZhou

Read the fucking source code

0%

Android - Jetpack套件之 Lifecycle 使用

发表于 更新于 分类于 阅读次数：

Android Jetpack 套件之 Lifecycle 使用；

Jetpack 和 Lifecycle

Jetpack 是一个由多个库组成的套件，可帮助开发者遵循最佳做法，减少样板代码并编写可在各种 Android 版本和设备中一致运行的代码，让开发者集中精力编写重要的代码。

Jetpack 组件包括 4 个方面：架构（Architecture）、基础（Architecture）、行为（Behavior）、界面（UI）：

Jetpack 架构

而 Lifecycle 是用于帮助开发者管理Activity和Fragment 的生命周期，它是LiveData和ViewModel的基础，属于 Android 架构组件；

Lifecycle 使用方式

1
getLifecycle().addObserver(Observer);

被观察者(LifecycleOwner)

被观察者需要实现 LifecycleOwner 接口，比如对于 Activity，Activity —> AppCompatActivity —> FragmentActivity —> ComponentActivity —> LifecycleOwner，最终实现 LifecycleOwner 接口;

观察者(Observer)

其中 Observer 有 3 种：LifecycleEventObserver、DefaultLifecycleObserver、LifecycleObserver；

LifecycleEventObserver 接口

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
getLifecycle().addObserver(new LifecycleEventObserver() {
    @Override
    public void onStateChanged(@NonNull LifecycleOwner source, @NonNull Lifecycle.Event event) {
        switch (event){
            case ON_CREATE:
                Log.d(TAG, "ON_CREATE");
                break;
            case ON_RESUME:
                Log.d(TAG, "ON_RESUME");
                break;
            //...
            case ON_ANY:
                Log.d(TAG, "ON_ANY");
                break;
        }
    }
});

DefaultLifecycleObserver 接口

1
2
3
4
5
6
7
8
9
10
11
12
getLifecycle().addObserver(new DefaultLifecycleObserver() {
    @Override
    public void onCreate(@NonNull LifecycleOwner owner) {
        Log.d(TAG, "ON_CREATE");
    }

    @Override
    public void onResume(@NonNull LifecycleOwner owner) {
        Log.d(TAG, "ON_RESUME");
    }

});

LifecycleObserver 接口

通过 OnLifecycleEvent 注解的方式实现

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
getLifecycle().addObserver(new LifecycleObserver() {
    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    void onCreate(LifecycleOwner owner) {
        Log.d(TAG, "ON_CREATE");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    void onResume(LifecycleOwner owner) {
        Log.d(TAG, "ON_RESUME");
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_ANY)
    void onAny(LifecycleOwner owner) {
        Log.d(TAG, "ON_ANY");
    }
});

使用注解的方式已经废弃

优先级

那么这三种方式的优先级是什么呢，我们来看看 LifecycleEventObserver 接口和 DefaultLifecycleObserver 接口的注释：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
/**
 * Class that can receive any lifecycle change and dispatch it to the receiver.
 * <p>
 * If a class implements both this interface and
 * {@link androidx.lifecycle.DefaultLifecycleObserver}, then
 * methods of {@code DefaultLifecycleObserver} will be called first, and then followed by the call
 * of {@link LifecycleEventObserver#onStateChanged(LifecycleOwner, Lifecycle.Event)}
 * <p>
 * If a class implements this interface and in the same time uses {@link OnLifecycleEvent}, then
 * annotations will be ignored.
 */
public interface LifecycleEventObserver extends LifecycleObserver {}

/**
 * Callback interface for listening to {@link LifecycleOwner} state changes.
 * If a class implements both this interface and {@link LifecycleEventObserver}, then
 * methods of {@code DefaultLifecycleObserver} will be called first, and then followed by the call
 * of {@link LifecycleEventObserver#onStateChanged(LifecycleOwner, Lifecycle.Event)}
 * <p>
 * If a class implements this interface and in the same time uses {@link OnLifecycleEvent}, then
 * annotations will be ignored.
 */
@SuppressWarnings("unused")
public interface DefaultLifecycleObserver extends FullLifecycleObserver {}

可以看出，如果一个观察者同时实现了 LifecycleEventObserver 和 DefaultLifecycleObserver，那么 DefaultLifecycleObserver 要先于 LifecycleEventObserver 执行，如果同时也添加了 OnLifecycleEvent 注解，那么注解部分会被忽略掉；

Reference

Donate comment here.