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。

ackage com.example.lifecycledemo1;

import android.arch.lifecycle.Lifecycle;
import android.arch.lifecycle.LifecycleObserver;
import android.arch.lifecycle.OnLifecycleEvent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        getLifecycle().addObserver(new MyObserver());//1
    }

    public class MyObserver implements LifecycleObserver{

        @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
        void onResume(){
            Log.d(TAG, "Lifecycle call onResume");
        }
        @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
        void onPause(){
            Log.d(TAG, "Lifecycle call onPause");
        }
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.d(TAG, "onResume");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.d(TAG, "onPause");

    }
}

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

public class MyPresenter implements IPresenter {
    private static final String TAG = "test";

    @Override
    public void onResume() {
        Log.d(TAG, "Lifecycle call onResume");
    }

    @Override
    public void onPause() {
        Log.d(TAG, "Lifecycle call onPause");
    }
}

interface IPresenter extends LifecycleObserver {

    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    void onResume();

    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    void onPause();
}

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：

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "test";
    private IPresenter mPresenter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mPresenter = new MyPresenter();
        getLifecycle().addObserver(mPresenter);
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.d(TAG, "onResume");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.d(TAG, "onPause");

    }
}

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MyPresent