Android 官方架构组件之 Lifecycle的学习

Lifecycle:官方介绍
Lifecycle is a class that holds the information about the lifecycle state of a component (like an activity or a fragment) and allows other objects to observe this state.
Lifecycle uses two main enumerations to track the lifecycle status for its associated component。
大概意思是：
生命周期它保存关于组件的生命周期状态（如Activity和Fragment）的信息，并允许其他对象观察此状态。
生命周期使用枚举来跟踪其相关组件的生命周期状态。看源码：（一个记录State，一个记录Event）。

 public static enum State {        DESTROYED,        INITIALIZED,        CREATED,        STARTED,        RESUMED;        private State() {        }        public boolean isAtLeast(@NonNull Lifecycle.State state) {            return this.compareTo(state) >= 0;        }    }    public static enum Event {        ON_CREATE,        ON_START,        ON_RESUME,        ON_PAUSE,        ON_STOP,        ON_DESTROY,        ON_ANY;        private Event() {        }    }

通过一个例子学会控制Activity的生命周期，在各生命周期完成事件：
首先定义一个接口，让其继承LifecycleObserver，在Activity实现此接口：

public interface LifecycleHelper extends LifecycleObserver {    @OnLifecycleEvent(Lifecycle.Event.ON_START)    void onStartLifecycle();    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)    void onCreateLifecycle();    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)    void onResumeLifecycle();    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)    void onPauseLifecycle();    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)    void onStopLifecycle();    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)    void onDestoryLifecycle();}

在onCreate()中订阅：

 getLifecycle().addObserver(this);

在onDestory()解订阅：

 getLifecycle().removeObserver(this);

如下：

public class TeastActivity extends AppCompatActivity implements LifecycleHelper {    @Override    protected void onCreate(@Nullable Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_teast);        getLifecycle().addObserver(this)；    }    @Override    protected void onDestroy() {        super.onDestroy();        getLifecycle().removeObserver(this);    }    @Override    public void onStartLifecycle() {    }        @Override    public void onCreateLifecycle() {    }    @Override    public void onResumeLifecycle() {    }    @Override    public void onPauseLifecycle() {    }    @Override    public void onStopLifecycle() {    }    @Override    public void onDestoryLifecycle() {    }}

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