为什么这个用于制作 5 秒计时器的简单修改（对工作代码）不起作用？

Question

我有一个简单的 C# 程序（我使用的是 Visual Studio 2010）-只需一个表单上的按钮-如下面最底部的链接所示- 当按下此按钮时，它会在消息框中显示每秒经过的时间。

这在这个程序中没有错误，它在下面给出并且完全工作。 它的工作原理是在按下按钮后将变量 starttodisplaytimeronscreen 设置为 true - 这是一个标志 - 并且一旦设置为 true 它可以显示每秒显示的消息框。 这是工作代码（我正在使用的完整程序）

using System;
using System.Timers;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace finitetimerprogram
{
public partial class Form1 : Form
{
 int thetimeinsecs = 0;// is the number of seconds as an integer that have elapsed since button pressed
  bool starttodisplaytimeronscreen = false;// this is a flag that set to true if button is pressed
  System.Timers.Timer mytimer = new System.Timers.Timer();

  private void customfn(object source, ElapsedEventArgs e)
        {
      if (starttodisplaytimeronscreen == true)
   {  // starttodisplaytimeronscreen becomes true if the button is clicked
                thetimeinsecs = thetimeinsecs + 1;
  MessageBox.Show("seconds since  pressed= " + thetimeinsecs.ToString(), "seconds since pressed= " + thetimeinsecs.ToString());
            }
        }

        public Form1()
        {  // this function is called continually from since when the form is shown onscreen
            InitializeComponent();
            mytimer.Elapsed += new ElapsedEventHandler(customfn);
            mytimer.Interval = 1000;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            starttodisplaytimeronscreen = true;
            mytimer.Start();
        }


    }
}

现在我想修改这个程序，让它在 5 秒后停止显示计时器- 换句话说，单击按钮会激活一个 5 秒计时器，该计时器显示为 在屏幕上显示为 1、2、3、4 和 5 秒的五个消息框。 然后，如果用户再次（再一次）按下按钮，则一旦计时器停止，它将再次启动 5 秒计时器（假设在这种情况下，每次用户想要创建 5 秒计时器时，仅单击一次按钮）。

我已经通过添加简单的代码来做到这一点

  if (thetimeinsecs > 5)
 {// this if statement stop the timer after 5 seconds but doesnt work
  starttodisplaytimeronscreen = false;// supposed to stop displaying the message box after 5 secods
  thetimeinsecs = 0;
   mytimer.Stop();
        }

在 5 秒后重置计时器，将标志 starttodisplaytimeronscreen 重置为 false。将 timeinsecs 重置为零，并使用 mytimer.Stop() 停止计时器。 我遇到的问题是这样一个简单的代码来修改工作代码（上面最初给出）以使 5 秒计时器不起作用。所以我的问题是为什么它不起作用？ - 有什么简单的方法来解决它？

下面是完整的非工作代码 - 只是为了清楚起见。

using System;
using System.Timers;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace finitetimerprogram
{
    public partial class Form1 : Form
    {
       int thetimeinsecs = 0;// is the number of seconds as an integer that have elapsed since button pressed
        bool starttodisplaytimeronscreen = false;// this is a flag that set to true if button is pressed
        System.Timers.Timer mytimer = new System.Timers.Timer();

        private void customfn(object source, ElapsedEventArgs e)
        {
            if (starttodisplaytimeronscreen == true)
            {  // starttodisplaytimeronscreen becomes true if the button is clicked
                thetimeinsecs = thetimeinsecs + 1;
                MessageBox.Show("seconds since  pressed= " + thetimeinsecs.ToString(), "seconds since pressed= " + thetimeinsecs.ToString());   
            }


            if (thetimeinsecs > 5)
            {// this if statment stop the timer after 5 seconds but doesnt work
                starttodisplaytimeronscreen = false;// supposed to stop displaying the message box after 5 secods
                thetimeinsecs = 0;
                mytimer.Stop();
            }

        }

        public Form1()
        {  // this function is called continually from since when the form is shown onscreen
            InitializeComponent();
            mytimer.Elapsed += new ElapsedEventHandler(customfn);
            mytimer.Interval = 1000;

        }

        private void button1_Click(object sender, EventArgs e)
        {
            starttodisplaytimeronscreen = true;
            mytimer.Start();
        }

shows what happens after 6 seconds since the button was pressed

Answer 1

简单的解决方法是如下所示交换你的函数行：

private void customfn(object source, ElapsedEventArgs e)
{
    if (thetimeinsecs >= 5)
    {// this if statment stop the timer after 5 seconds but doesnt work
        starttodisplaytimeronscreen = false;// supposed to stop displaying the message box after 5 secods
        thetimeinsecs = 0;
        mytimer.Stop();
    }

    if (starttodisplaytimeronscreen == true)
    {  // starttodisplaytimeronscreen becomes true if the button is clicked
        thetimeinsecs = thetimeinsecs + 1;
        MessageBox.Show("seconds since  pressed= " + thetimeinsecs.ToString(), "seconds since pressed= " + thetimeinsecs.ToString());
    }

}

如果你想进一步改进它，你可以通过稍微改变逻辑来摆脱starttodisplaytimeronscreen。我会把它留给你。