如何防止C＃中的表单的keydown事件多次触发？ [英] How can I prevent the keydown event of a form in C# from firing more than once?

问题描述

根据官方文档，KeyDown事件在Windows窗体控件只发生一次，但是很容易证明该事件会一直按住一个键：

  private void textBox1_KeyDown（object sender，KeyEventArgs e）
 {
 label1.Text = string.Format（{0}，globalCounter ++）; 
} 
  

你如何消费这个事件，使它只能触发一次？

解决方案

我通常是一个VB人，但这似乎适用于我作为演示代码，使用表单本身作为输入源：

 命名空间WindowsFormsApplication1 
 {
 public partial class Form1：Form 
 {
 private bool _keyHeld; 
 public Form1（）
 {
 InitializeComponent（）; 
 this.KeyUp + = new KeyEventHandler（Form1_KeyUp）; 
 this.KeyDown + = new KeyEventHandler（Form1_KeyDown）; 
 this._keyHeld = false; 
} 
 
 void Form1_KeyUp（object sender，KeyEventArgs e）
 {
 this._keyHeld = false; 
} 
 
 void Form1_KeyDown（object sender，KeyEventArgs e）
 {
 if（！this._keyHeld）
 {
 this._keyHeld = true; 
 if（this.BackColor == Control.DefaultBackColor）
 {
 this.BackColor = Color.Red; 
} 
 else 
 {
 this.BackColor = Control.DefaultBackColor; 
} 
} 
 else 
 {
 e.Handled = true; 
} 
} 
} 
} 
  

如果您一次按住多个键，则逻辑会略有粗略，但是似乎只是从最后一个按键被触发事件，所以我不认为这是一个问题。 >

我在VB中的TextBox中测试了这个，它工作正常。不知道在c＃中应该遵循的继承约定，所以我把它作为这个答案的直接表单。

再次对任何总代码格式化错误表示歉意，这不是我惯用的语言。

According to the official documentation, the KeyDown event on a Windows Forms control occurs only once, but it is easy to demonstrate that the event fires continually aslong as a key is held down:

    private void textBox1_KeyDown(object sender, KeyEventArgs e)
    {
        label1.Text = string.Format("{0}", globalCounter++);
    }

How can you consume the event so that it fires only once?

解决方案

I'm generally a VB guy, but this seems to work for me as demo code, using the form itself as the input source:

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        private bool _keyHeld;
        public Form1()
        {
            InitializeComponent();
            this.KeyUp += new KeyEventHandler(Form1_KeyUp);
            this.KeyDown += new KeyEventHandler(Form1_KeyDown);
            this._keyHeld = false;
        }

        void Form1_KeyUp(object sender, KeyEventArgs e)
        {
            this._keyHeld = false;
        }

        void Form1_KeyDown(object sender, KeyEventArgs e)
        {
            if (!this._keyHeld)
            {
                this._keyHeld = true;
                if (this.BackColor == Control.DefaultBackColor)
                {
                    this.BackColor = Color.Red;
                }
                else
                {
                    this.BackColor = Control.DefaultBackColor;
                }
            }
            else
            {
                e.Handled = true;
            }
        }
    }   
}

I think the logic gets a little sketchy if you're holding down multiple keys at a time, but that seems to only fire the event from the last key that was pressed anyway, so I don't think it becomes an issue.

I tested this in a TextBox in VB, and it worked fine. Wasn't sure on the inheritance conventions I should follow in c#, so I left it as a straight Form for this answer.

Apologies for any gross code formatting errors, again, this isn't my usual language.

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