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">

    <Button
        android: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" />

    <TextView
        android: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" />

    <Button
        android: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" />

    <Button
        android: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" />

    <Button
        android: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
//2024.12.30

import 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;
    @Override
    protected 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() {
            @Override
            public void onClick(View v) {
                clearTimer();
            }
        });
        btnStart.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (!isRunning) {
                    startTime = System.currentTimeMillis();
                    isRunning = true;
                    handler.postDelayed(updateTimer, 0);
                }
            }
        });

        btnPause.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (isRunning &&!isPaused) {
                    isPaused = true;
                    elapsedTime += System.currentTimeMillis() - startTime;
                    handler.removeCallbacks(updateTimer);
                }
            }
        });

        btnResume.setOnClickListener(new View.OnClickListener() {
            @Override
            public 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() {
        @Override
        public 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);
            }
        }
    };
}