如何将 Timer 传递给 EventHandler？

Question

我想要的是有一个ComboBox，它在SelectedIndexChanged 上会改变一个Timer.Interval。我的代码基本上是这样的：

public Form1()
{
    InitializeComponent();
    Timer AutoRefresh = new Timer();
    AutoRefresh.Tick += new EventHandler(AutoRefresh_Tick);
    var RefreshIntervals = new[] { "4 hours", "2 hours", "1 hour", "15 minutes", "10 seconds" };
    comboBox1.DataSource = RefreshIntervals;
    comboBox1.SelectedIndexChanged += new EventHandler(comboBox1_SelectedIndexChanged);
}

void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    if (AutoRefresh.Enabled == true)
        AutoRefresh.Enabled = false;
    if (comboBox1.SelectedText == "4 hours")
        AutoRefresh.Interval = 14400000;
    else if (comboBox1.SelectedText == "2 hours")
        AutoRefresh.Interval = 7200000;
    else if (comboBox1.SelectedText == "1 hour")
        AutoRefresh.Interval = 3600000;
    else if (comboBox1.SelectedText == "15 minutes")
        AutoRefresh.Interval = 900000;
    else if (comboBox1.SelectedText == "10 seconds")
        AutoRefresh.Interval = 10000;
    AutoRefresh.Enabled = true;
}

现在，显然这不起作用，因为 comboBox1_SelectedIndexChanged() 没有对 Timer 变量的引用。

如何修改我的代码以将AutoRefresh 传递给comboBox1_SelectedIndexChanged()？

也许是指出我还是 C# 新手的好时机。请善待。

Answer 1

一种方法是将 Time 对象声明为类的成员。然后你就可以在事件中访问它了。

你也应该删除'throw new NotImplementedException();'来自您的事件，因为此语句引发异常

Answer 2

在字段中提取局部变量表单构造函数，现在计时器将在处理程序中可见

Timer AutoRefresh;   
public Form1()
{
  InitializeComponent();
 AutoRefresh = new Timer();
  AutoRefresh.Tick += new EventHandler(AutoRefresh_Tick);

 resh.Interval = 10000;
  AutoRefresh.Enabled = true;

}

Answer 3

根据您的评论，SqlDependency 类可能对您很有效：

...程序...查询填充DataTable 以进行显示的SQL DB。我想用这个组合框和 Timer 来自动刷新 DataTable ...

Answer 4

您需要将计时器放入您班级的field。

Answer 5

我在你的代码中发现一个错误

void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
  throw new NotImplementedException(); // remove this line

Answer 6

我做了一些重构，发现代码中有另一个错误 看看这个方法在我的项目中可以正常工作

void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (AutoRefresh.Enabled)
            AutoRefresh.Enabled = false;
        var selectedItem = comboBox1.SelectedItem.ToString();

        switch (selectedItem)
        {
            case "4 hours":
                AutoRefresh.Interval = 14400000;
                break;
            case "2 hours":
                AutoRefresh.Interval = 7200000;
                break;
            case "1 hour":
                AutoRefresh.Interval = 3600000;
                break;
            case "15 minutes":
                AutoRefresh.Interval = 900000;
                break;
            case "10 seconds":
                AutoRefresh.Interval = 10000;
                break;
        }
        AutoRefresh.Enabled = true;
    }

您应该使用 SelectedItem 属性而不是 SelectedText

Answer 7

namespace WindowsFormsApplication1
{
    using System;
    using System.Windows.Forms;

    public partial class Form1 : Form
    {
        /// <summary>
        /// The default constructor.
        /// I used the designer, so the InitializeComponent method contains the timer and combobox initialization.
        /// </summary>
        public Form1()
        {
            InitializeComponent();
        }

        /// <summary>
        /// Occurs when the combo box selection changes.
        /// </summary>
        /// <param name="sender">The sender object, i.e., the combobox</param>
        /// <param name="e">The event arguments.</param>
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (autoRefresh.Enabled == true)
            {
                autoRefresh.Enabled = false;
            }

            // so I can easily change the time scale when debugging, I'm using a multiplier
            const int multiplier = 10000;

            // notice I'm using SelectedItem because the event triggered was index changed, not text changed
            var selectedInterval = comboBox1.SelectedItem.ToString();

            // if a valid entry wasn't selected, then we'll disable the timer
            var enabled = true;

            switch (selectedInterval)
            {
                case "4 hours":
                    autoRefresh.Interval = 1440 * multiplier;
                    break;
                case "2 hours":
                    autoRefresh.Interval = 720 * multiplier;
                    break;
                case "1 hour":
                    autoRefresh.Interval = 360 * multiplier;
                    break;
                case "15 minutes":
                    autoRefresh.Interval = 90 * multiplier;
                    break;
                case "10 seconds":
                    autoRefresh.Interval = 1 * multiplier;
                    break;
                default:
                    // we didn't choose a valid entry, or picked blank line
                    enabled = false;
                    break;
            }

            autoRefresh.Enabled = enabled;
        }

        /// <summary>
        /// Occurs every time the timer reaches its interval
        /// </summary>
        /// <param name="sender">The sender object, i.e., the timer.</param>
        /// <param name="e">The event arguments.</param>
        private void AutoRefresh_Tick(object sender, EventArgs e)
        {
            // to ensure the next timer triggers at the desired interval
            // stop the timer while doing the operations in this method (they could be lengthy)
            // and then restart the timer before exiting
            autoRefresh.Enabled = false;

            // give a visual indicator of the timer ticking.
            // Here is where you would do your DB operation.
            MessageBox.Show(string.Format("Hello! time={0}:{1}", DateTime.Now.ToLongTimeString(), DateTime.Now.Millisecond));

            autoRefresh.Enabled = true;
        }
    }
}