Lifecycle 是一个持有(如 Activity 或 Fragment )生命周期状态信息的类,并且允许其它对象观察这个状态。从而在外部实现监听,能够使我们及时释放资源,避免内存泄露和程序崩溃。
常见的观察生命周期的方式,如MVP中在 Presenter 中对 Activity 或 Fragment 的生命周期进行观察,我们要在 Presenter 中定义方法,在 Activity 或 Fragment 中调用,通过这种方式进行观察,这样代码量大而且也比较繁琐,使用 Lifecycle 组件就能简化很多,下面通过 Lifecycle 与 Presenter 管理生命周期的方式进行比较。
在 Presenter 中处理 Activity 和 Fragment 的生命周期,如下:
// 定义Contract
public interface ContentContract {
// ......
abstract class Presenter {
public abstract void onCreate();
public abstract void onStart();
public abstract void onResume();
public abstract void onStop();
public abstract void onPause();
public abstract void onDestroy();
}
}
// 定义Presenter
public class ContentPresenter extends ContentContract.Presenter {
private static final String TAG = ContentPresenter.class.getSimpleName();
@Override
public void onCreate() {
Log.e(TAG, "Presenter ----- onCreate()");
}
@Override
public void onStart() {
Log.e(TAG, "Presenter ----- onStart()");
}
@Override
public void onResume() {
Log.e(TAG, "Presenter ----- onResume()");
}
@Override
public void onStop() {
Log.e(TAG, "Presenter ----- onStop()");
}
@Override
public void onPause() {
Log.e(TAG, "Presenter ----- onPause()");
}
@Override
public void onDestroy() {
Log.e(TAG, "Presenter ----- onDestroy()");
}
}
// Activity中使用
public class ContentActivity extends AppCompatActivity {
private ContentPresenter mPresenter = new ContentPresenter();
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_content);
mPresenter.onCreate();
}
@Override
protected void onStart() {
super.onStart();
mPresenter.onStart();
}
@Override
protected void onResume() {
super.onResume();
mPresenter.onResume();
}
@Override
protected void onPause() {
super.onPause();
mPresenter.onPause();
}
@Override
protected void onStop() {
super.onStop();
mPresenter.onStop();
}
@Override
protected void onDestroy() {
super.onDestroy();
mPresenter.onDestroy();
}
}
需要实现 LifecycleObserver 接口,并添加事件注解。
// 定义Lifecycle
public class MainLifecycleListener implements LifecycleObserver {
private static final String TAG = MainLifecycleListener.class.getSimpleName();
@OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
public void onCreate() {
Log.e(TAG, "LifecycleObserver ----- onCreate()");
}
@OnLifecycleEvent(Lifecycle.Event.ON_START)
public void onStart() {
Log.e(TAG, "LifecycleObserver ----- onStart()");
}
@OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
public void onResume() {
Log.e(TAG, "LifecycleObserver ----- onResume()");
}
@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
public void onStop() {
Log.e(TAG, "LifecycleObserver ----- onStop()");
}
@OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
public void onPause() {
Log.e(TAG, "LifecycleObserver ----- onPause()");
}
@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
public void onDestroy() {
Log.e(TAG, "LifecycleObserver ----- onDestroy()");
}
/**
* 每次生命周期发生变化时都会被触发
*/
// @OnLifecycleEvent(Lifecycle.Event.ON_ANY)
// public void onAny(){
// Log.e(TAG, "LifecycleObserver ----- onAny()");
// }
}
public class MainActivity extends AppCompatActivity {
private MainLifecycleListener mListener = new MainLifecycleListener();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// 添加观察者
getLifecycle().addObserver(mListener);
}
@Override
protected void onDestroy() {
super.onDestroy();
// 移除观察者
getLifecycle().removeObserver(mListener);
}
}
可以看到代码量少了很多,简化了很多,观察生命周期也比较简单。