android studio 写一个小计时器（版本二）

as版本：23.3.1patch2

例程：timer

在前一个版本的基本上改的，增加了继续的功能，实现方法稍微不同。

动画演示：

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:id="@+id/main"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".MainActivity"><Buttonandroid:id="@+id/btn_clear"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_marginStart="144dp"android:layout_marginTop="60dp"android:text="清零"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toBottomOf="@+id/btn_stop" /><TextViewandroid:id="@+id/tv_timer"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="Hello World!"android:textSize="30dp"app:layout_constraintBottom_toBottomOf="parent"app:layout_constraintEnd_toEndOf="parent"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toTopOf="parent"app:layout_constraintVertical_bias="0.272" /><Buttonandroid:id="@+id/btn_start"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_marginStart="36dp"android:layout_marginTop="80dp"android:text="开始"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toBottomOf="@+id/tv_timer" /><Buttonandroid:id="@+id/btn_stop"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_marginStart="20dp"android:text="暂停"app:layout_constraintStart_toEndOf="@+id/btn_start"app:layout_constraintTop_toTopOf="@+id/btn_start" /><Buttonandroid:id="@+id/btn_resume"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_marginStart="20dp"android:text="继续"app:layout_constraintStart_toEndOf="@+id/btn_stop"app:layout_constraintTop_toTopOf="@+id/btn_stop" /></androidx.constraintlayout.widget.ConstraintLayout>

mainactivity.java

package com.shudu.timer;
//按钮控制显示计时器。
//开始、暂停、继续、清零四个按钮
//2024.12.30import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;public class MainActivity extends AppCompatActivity {private TextView tvTimer;private Button btnStart, btnPause, btnResume,btnClear;private Handler handler = new Handler();private long startTime=0;private long elapsedTime = 0;private Runnable timerRunnable;private boolean isRunning = false;private boolean isPaused = false;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);EdgeToEdge.enable(this);setContentView(R.layout.activity_main);ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);return insets;});tvTimer = findViewById(R.id.tv_timer);btnStart = findViewById(R.id.btn_start);btnPause = findViewById(R.id.btn_stop);btnResume = findViewById(R.id.btn_resume);btnClear=findViewById(R.id.btn_clear);btnClear.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {clearTimer();}});btnStart.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if (!isRunning) {startTime = System.currentTimeMillis();isRunning = true;handler.postDelayed(updateTimer, 0);}}});btnPause.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if (isRunning &&!isPaused) {isPaused = true;elapsedTime += System.currentTimeMillis() - startTime;handler.removeCallbacks(updateTimer);}}});btnResume.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if (isPaused) {isPaused = false;startTime = System.currentTimeMillis();handler.postDelayed(updateTimer, 0);}}});}private void clearTimer() {isRunning = false;
//        startTime=0;startTime = System.currentTimeMillis();//这行代码什么意思,不写还不行。写成starttime=0也不行。tvTimer.setText("00:00:00");}private Runnable updateTimer = new Runnable() {@Overridepublic void run() {long currentTime;if (isRunning) {if (isPaused) {currentTime = elapsedTime;} else {currentTime = System.currentTimeMillis() - startTime + elapsedTime;}int seconds = (int) (currentTime / 1000);int minutes = seconds / 60;int hours = minutes / 60;seconds %= 60;minutes %= 60;tvTimer.setText(String.format("%02d:%02d:%02d", hours, minutes, seconds));handler.postDelayed(this, 1000);}}};
}