LifeCycles的认识

简化关于生命周期回调的代码;

计时器例子

package com.esdut.lifecycles;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.os.SystemClock;
import android.widget.Chronometer;
//stop() 只能停止视图刷新 不能影响时间的停留
public class MainActivity extends AppCompatActivity {
    Chronometer chronometer;
    private long esapsedTime;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        chronometer = findViewById(R.id.meter);
//        chronometer.setBase(System.currentTimeMillis()); //UNIX 时间  1970 1-1 到现在为止的毫秒数
//        chronometer.setBase(SystemClock.elapsedRealtime());//手机从上一次开机到现在, 只跟系统启动有关
        //不写的话系统自动帮写SystemClock.elapsedRealtime()
        chronometer.start();
    }

    @Override
    protected void onPause() {
        super.onPause();
        esapsedTime = SystemClock.elapsedRealtime() - chronometer.getBase();
        chronometer.stop();
    }

    @Override
    protected void onResume() {
        super.onResume();
        chronometer.setBase(SystemClock.elapsedRealtime() - esapsedTime);
        chronometer.start();
    }
}

改进 —> 新建观察者类

package com.esdut.lifecycles;

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

import androidx.annotation.NonNull;
import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.LifecycleEventObserver;
import androidx.lifecycle.LifecycleOwner;
import androidx.lifecycle.OnLifecycleEvent;

public class MyChronometer extends Chronometer implements LifecycleEventObserver {
    private long elapsedTime;
    public MyChronometer(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    private void pauseMeter() {
        elapsedTime = SystemClock.elapsedRealtime() - getBase();
    }
    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    private void resumeMeter(){
        setBase(SystemClock.elapsedRealtime() - elapsedTime);
        start();
    }

    @Override
    public void onStateChanged(@NonNull LifecycleOwner source, @NonNull Lifecycle.Event event) {

    }
}