Jetpack架构组件Lifecycle使用

Posted 2022-12-14 ganchuanpu

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