[移动开发]LifecycleObserver解耦Activity和组件

实现一个监视看手机时长的应用
自定义MyChronometer

package com.example.jetpack;

import android.content.Context;
import android.os.SystemClock;
import android.util.AttributeSet;
import android.widget.Chronometer;

import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.LifecycleObserver;
import androidx.lifecycle.OnLifecycleEvent;

import java.util.Observer;

public class MyChronometer extends Chronometer implements LifecycleObserver {
    long pauseTime;
    public MyChronometer(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    public void onStart(){
        setBase(SystemClock.elapsedRealtime()-pauseTime);
        start();
    }
    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    public void onStop(){
        pauseTime=SystemClock.elapsedRealtime()-getBase();
        stop();
    }
}

添加lifecycle监听

//        不要忘记add生命周期监听，否则lifecycle无效
        getLifecycle().addObserver(chronometer);

package com.example.jetpack;

import android.os.Bundle;
import android.os.SystemClock;
import android.widget.Chronometer;

import androidx.appcompat.app.AppCompatActivity;

public class MainLifeCycleActivity extends AppCompatActivity {
    private MyChronometer chronometer;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        chronometer = (MyChronometer) findViewById(R.id.chronometer);
//        不要忘记add生命周期监听，否则lifecycle无效
        getLifecycle().addObserver(chronometer);

    }


}

<?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"
 >

    <com.example.jetpack.MyChronometer
        android:id="@+id/chronometer"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>