Lifecycle解耦页面和组件

不使用lifecycle，对程序运行时间进行监控。组件和activity高度耦合（为了实现在后台，不计算程序运行时间）

public class MainActivity extends AppCompatActivity {
    private static final String TAG ="MainActivity" ;
    Chronometer Chronometer;
    Long el=0L;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d(TAG, "onCreate:创建");
        Chronometer = findViewById(R.id.Chronometer);
    }
    @Override
    protected void onResume() {
        Log.d(TAG, "onResume: 可交互");
        super.onResume();
        Chronometer.setBase(SystemClock.elapsedRealtime()-el);
        Chronometer.start();
    }
    @Override
    protected void onStop() {
        Log.d(TAG, "onStop: 后台");
        super.onStop();
        el = SystemClock.elapsedRealtime() - Chronometer.getBase();
        Chronometer.stop();
    }
}

使用lifecycle
我们自定义组件，继承chronometer并实现lifecycle里面的方法。

public class MyChronometer extends Chronometer implements LifecycleObserver {
    long el=0L;
    public MyChronometer(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    private void startMeter(){
     setBase(SystemClock.elapsedRealtime()-el);
     start();
    }
    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
  private void stopMeter(){
        el=SystemClock.elapsedRealtime()-getBase();
        stop();
  }
}

在activity里面

public class Chronometer02Activity extends AppCompatActivity {
   private MyChronometer chronometer;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chronometer);
        chronometer =findViewById(R.id.Chronometer_2);
        getLifecycle().addObserver(chronometer);
    }
}

布局文件

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".Chronometer02Activity">
    <com.example.lifecycletest01.MyChronometer
        android:id="@+id/Chronometer_2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="34sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>