android(计时器)

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical">

    <Chronometer
        android:id="@+id/chronometer"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:textColor="#ff0000"
        android:textSize="60dip" />

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_margin="10dip"
        android:orientation="horizontal">

        <Button
            android:id="@+id/btnStart"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="开始记时" />

        <Button
            android:id="@+id/btnStop"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="停止记时" />

        <Button
            android:id="@+id/btnReset"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="重置" />

        <Button
            android:id="@+id/btn_format"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="格式化" />
    </LinearLayout>


</LinearLayout>

MainActivity.java

package com.example.myapplication3;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.os.SystemClock;
import android.view.View;
import android.widget.Button;
import android.widget.Chronometer;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener, Chronometer.OnChronometerTickListener {
    
    

    private Chronometer chronometer;
    private Button btn_start,btn_stop,btn_base,btn_format;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
    }

    private void initView() {
    
    
        chronometer = (Chronometer) findViewById(R.id.chronometer);
        btn_start = (Button) findViewById(R.id.btnStart);
        btn_stop = (Button) findViewById(R.id.btnStop);
        btn_base = (Button) findViewById(R.id.btnReset);
        btn_format = (Button) findViewById(R.id.btn_format);

        chronometer.setOnChronometerTickListener(this);
        btn_start.setOnClickListener(this);
        btn_stop.setOnClickListener(this);
        btn_base.setOnClickListener(this);
        btn_format.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
    
    
        switch (v.getId()){
    
    
            case R.id.btnStart:
                chronometer.start();// 开始计时
                break;
            case R.id.btnStop:
                chronometer.stop();// 停止计时
                break;
            case R.id.btnReset:
                chronometer.setBase(SystemClock.elapsedRealtime());// 复位
                break;
            case R.id.btn_format:
                chronometer.setFormat("Time：%s");// 更改时间显示格式
                break;
        }

    }

    @Override
    public void onChronometerTick(Chronometer chronometer) {
    
    
        String time = chronometer.getText().toString();
        if(time.equals("00:00")){
    
    
            Toast.makeText(MainActivity.this,"时间到了~",Toast.LENGTH_SHORT).show();
        }
        
    }
}

效果图：