Jetpack架構組件（二）Lifecycle使用

1.直接添加如下依賴就可以滿足日常的作業，如果缺少哪個庫，再去單獨添加就好了

implementation "android.arch.lifecycle:extensions:1.1.1"

添加這一句代碼就依賴了如下的庫，

2.先不談Activity和Fragment中如何使用，先舉一個Lifecycle的簡單例子，

 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     @Override15     protected void onCreate(Bundle savedInstanceState) {16         super.onCreate(savedInstanceState);17         setContentView(R.layout.activity_main);18         getLifecycle().addObserver(new MyObserver());//119     }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     @Override34     protected void onResume() {35         super.onResume();36         Log.d(TAG, "onResume");37     }38 39     @Override40     protected void onPause() {41         super.onPause();42         Log.d(TAG, "onPause");43 44     }45 }

先實作MyObserver，對ON_CREATE和ON_RESUME事件進行監聽，因為在Android Support Library 26.1.0 及其之后的版本，Activity和Fragment已經默認實作了LifecycleOwner介面，所以在注釋1處可以直接使用getLifecycle方法獲取Lifecycle物件，這樣MyObserver就可以觀察MainActivity的生命周期變化了，LifecycleOwner可以理解為被觀察者，MainActivity默認實作了LifecycleOwner介面，也就是說MainActivity是被觀察者，
運行程式，列印的log如下所示，

D/MainActivity: onResumeD/MainActivity: Lifecycle call onResumeD/MainActivity: Lifecycle call onPauseD/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     @Override10     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介面繼承自LifecycleObserver介面，MyPresenter又實作了IPresenter介面，這樣MyPresenter成為了一個觀察者，
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     @Override14     protected void onResume() {15         super.onResume();16         Log.d(TAG, "onResume");17     }18 19     @Override20     protected void onPause() {21         super.onPause();22         Log.d(TAG, "onPause");23 24     }25 }

MainActivity成為了被觀察者，當它的生命周期發生變化時，MyPresenter就可以觀察到，這樣就不需要在MainActivity的多個生命周期方法中呼叫MyPresenter的方法了，
列印的日志如下：

D/test: onResumeD/test: Lifecycle call onResumeD/test: Lifecycle call onPauseD/test: onPause

標籤：Android

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