Lifecycles

Lifecycles

计时器

• activity_main.xml

<?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=".MainActivity">

    <com.example.mylifecycles.MyChronometer
        android:id="@+id/meter"
        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>

• MainActivity.java

package com.example.mylifecycles;

import androidx.appcompat.app.AppCompatActivity;

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

public class MainActivity extends AppCompatActivity {

    private MyChronometer chronometer;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        chronometer = findViewById(R.id.meter);
        getLifecycle().addObserver(chronometer);

    }
}

• MyChronometer.java

package com.example.mylifecycles;

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;

public class MyChronometer extends Chronometer implements LifecycleObserver {
    private static long elapsedTime; // static 时，屏幕旋转时时间不会复位

    public MyChronometer(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    private void pauseMeter(){
        elapsedTime = SystemClock.elapsedRealtime() - getBase();
        stop();
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    private void resumeMeter(){
        setBase(SystemClock.elapsedRealtime() - elapsedTime);
        start();
    }
}