1.直接添加如下依赖就可以满足日常的工作，如果缺少哪个库，再去单独添加就好了
- implementation "android.arch.lifecycle:extensions:1.1.1"
添加这一句代码就依赖了如下的库。
2.先不谈Activity和Fragment中如何使用，先举一个Lifecycle的简单例子。
- 1 ackage com.example.lifecycledemo1;
- 2
- 3 import android.arch.lifecycle.Lifecycle;
- 4 import android.arch.lifecycle.LifecycleObserver;
- 5 import android.arch.lifecycle.OnLifecycleEvent;
- 6 import android.support.v7.app.AppCompatActivity;
- 7 import android.os.Bundle;
- 8 import android.util.Log;
- 9
- 10 public class MainActivity extends AppCompatActivity {
- 11
- 12 private static final String TAG = "MainActivity";
- 13
- 14 @Override
- 15 protected void onCreate(Bundle savedInstanceState) {
- 16 super.onCreate(savedInstanceState);
- 17 setContentView(R.layout.activity_main);
- 18 getLifecycle().addObserver(new MyObserver());//1
- 19 }
- 20
- 21 public class MyObserver implements LifecycleObserver{
- 22
- 23 @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
- 24 void onResume(){
- 25 Log.d(TAG, "Lifecycle call onResume");
- 26 }
- 27 @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
- 28 void onPause(){
- 29 Log.d(TAG, "Lifecycle call onPause");
- 30 }
- 31 }
- 32
- 33 @Override
- 34 protected void onResume() {
- 35 super.onResume();
- 36 Log.d(TAG, "onResume");
- 37 }
- 38
- 39 @Override
- 40 protected void onPause() {
- 41 super.onPause();
- 42 Log.d(TAG, "onPause");
- 43
- 44 }
- 45 }
先实现MyObserver，对ON_CREATE和ON_RESUME事件进行监听。因为在Android Support Library 26.1.0 及其之后的版本，Activity和Fragment已经默认实现了LifecycleOwner接口，所以在注释1处可以直接使用getLifecycle方法获取Lifecycle对象，这样MyObserver就可以观察MainActivity的生命周期变化了，LifecycleOwner可以理解为被观察者，MainActivity默认实现了LifecycleOwner接口，也就是说MainActivity是被观察者。
运行程序，打印的log如下所示。
- D/MainActivity: onResume
- D/MainActivity: Lifecycle call onResume
- D/MainActivity: Lifecycle call onPause
- D/MainActivity: onPause
3.MVP的例子
- 1 public class MyPresenter implements IPresenter {
- 2 private static final String TAG = "test";
- 3
- 4 @Override
- 5 public void onResume() {
- 6 Log.d(TAG, "Lifecycle call onResume");
- 7 }
- 8
- 9 @Override
- 10 public void onPause() {
- 11 Log.d(TAG, "Lifecycle call onPause");
- 12 }
- 13 }
- 14
- 15 interface IPresenter extends LifecycleObserver {
- 16
- 17 @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
- 18 void onResume();
- 19
- 20 @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
- 21 void onPause();
- 22 }
IPresenter接口继承自LifecycleObserver接口，MyPresenter又实现了IPresenter接口，这样MyPresenter成为了一个观察者。
接在在MainActivity中加入MyPresenter：
- 1 public class MainActivity extends AppCompatActivity {
- 2
- 3 private static final String TAG = "test";
- 4 private IPresenter mPresenter;
- 5 @Override
- 6 protected void onCreate(Bundle savedInstanceState) {
- 7 super.onCreate(savedInstanceState);
- 8 setContentView(R.layout.activity_main);
- 9 mPresenter = new MyPresenter();
- 10 getLifecycle().addObserver(mPresenter);
- 11 }
- 12
- 13 @Override
- 14 protected void onResume() {
- 15 super.onResume();
- 16 Log.d(TAG, "onResume");
- 17 }
- 18
- 19 @Override
- 20 protected void onPause() {
- 21 super.onPause();
- 22 Log.d(TAG, "onPause");
- 23
- 24 }
- 25 }
MainActivity成为了被观察者，当它的生命周期发生变化时，MyPresenter就可以观察到，这样就不需要在MainActivity的多个生命周期方法中调用MyPresenter的方法了。
打印的日志如下：
- D/test: onResume
- D/test: Lifecycle call onResume
- D/test: Lifecycle call onPause
- D/test: onPause
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