private void tBox_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.KeyChar == 0x20) e.KeyChar = (char)0;  //禁止空格键
            if ((e.KeyChar == 0x2D) && (((TextBox)sender).Text.Length == 0)) return;   //处理负数
            if (e.KeyChar > 0x20)
            {
                try
                {
                    double.Parse(((TextBox)sender).Text + e.KeyChar.ToString());
                }
                catch
                {
                    e.KeyChar = (char)0;   //处理非法字符
                }
            }
        }

private void TextBox_KeyPress(object sender, KeyPressEventArgs e)
   {
    if(e.KeyChar!=8&&!Char.IsDigit(e.KeyChar))
    {
      e.Handled = true;
    }
   }
或者private void TextBox_KeyPress(object sender, KeyPressEventArgs e)
   {
    if(e.KeyChar!='\b'&&!Char.IsDigit(e.KeyChar))
    {
      e.Handled = true;
    }

}

private void textBox1_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
if(e.KeyChar!='\b')//这是允许输入退格键
{
if((e.KeyChar<'0')||(e.KeyChar>'9'))//这是允许输入0-9数字
{
e.Handled = true;
}
}
} 

private void button1_Click(object sender, EventArgs e) 
{ 
string text = this.textBox1.Text; 
if (text != null) 
MessageBox.Show(text); 
} 

private void textBox1_Validating(object sender, CancelEventArgs e) 
{ 
const string pattern = @"^\d+\.?\d+$"; 
string content = ((TextBox)sender).Text; 

if (!(Regex.IsMatch(content, pattern))) 
{ 
errorProvider1.SetError((Control)sender, "只能输入数字!"); 
e.Cancel = true; 
} 
else 
errorProvider1.SetError((Control)sender, null); 
}

private void textBox1_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
if(e.KeyChar=='.' && this.textBox1.Text.IndexOf(".")!=-1)
{
e.Handled=true;
}

if(!((e.KeyChar>=48 && e.KeyChar<=57) || e.KeyChar=='.' || e.KeyChar==8))
{
e.Handled=true;
}

}

  private void tbx_LsRegCapital_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (!Char.IsNumber(e.KeyChar) && !Char.IsPunctuation(e.KeyChar) && !Char.IsControl(e.KeyChar))
            {
                e.Handled = true;//消除不合适字符
            }
            else if (Char.IsPunctuation(e.KeyChar))
            {
                if (e.KeyChar != '.' || this.textBox1.Text.Length == 0)//小数点
                {
                    e.Handled = true;
                }
                if (textBox1.Text.LastIndexOf('.') != -1)
                {
                    e.Handled = true;
                }
            }      
        }

利用ASCII码处理办法、
{

            if ((e.KeyChar <= 48 || e.KeyChar >=57) && (e.KeyChar != 8) && (e.KeyChar != 46))
              e.Handled = true;
================48代表0，57代表9，8代表空格，46代表小数点
}

C#设置textBox只能输入数字（正数，负数，小数）简单实现

C#中设置TextBox控件中仅可以输入数字且设置上限

首先设置只可以输入数字：

　　首先设置TextBox控件的KeyPress事件：当用户按下的键盘的键不在数字位的话，就禁止输入

1    private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
2         {
3             if (e.KeyChar != 8 && !Char.IsDigit(e.KeyChar))//如果不是输入数字就不让输入
4             {
5                 e.Handled = true;
6             }
7         }

设置上限：

　　设置TextBox的TextChanged事件如下

 1  private void textBox1_TextChanged(object sender, EventArgs e)
 2         {
 3             int iMax = 100;//首先设置上限值
 4             if (textBox1.Text != null && textBox1.Text != "")//判断TextBox的内容不为空，如果不判断会导致后面的非数字对比异常
 5             {
 6                 if (int.Parse(textBox1.Text) > iMax)//num就是传进来的值,如果大于上限（输入的值），那就强制为上限-1，或者就是上限值？
 7                 {
 8                     textBox1.Text = (iMax - 1).ToString();
 9                 }
10             }
11         }

C#  winform中文本框限制只能输入数字和字母，退格键：

选择文本框的KeyPress事件，添加以下代码