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
}

来自：http://bbs.bccn.net/thread-205138-1-1.html