C#文本框中只能接受数字，其他字符不予处理

1、添加了一个Windows窗体Form1，在Form1中添加了一个文本框textBox1
2、在textBox1的KeyDown()事件中加入了以下代码：
private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
if ( e.KeyValue < 48 && e.KeyValue >57 ) //如果输入的字符是从 ‘0’ 到 ‘9’
{
//什么都不做
}
else
{
e.Handled=true; //如果输入的是非数字字符，则提前将这个事件结束掉，而不添加
MessageBox.Show( e.Handled.ToString() ）；
}
}
没写完，待续...
MSDN上的例子

[C#]
// Boolean flag used to determine when a character other than a number is entered.
private bool nonNumberEntered = false;

// Handle the KeyDown event to determine the type of character entered into the control.
private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
// Initialize the flag to false.
nonNumberEntered = false;

// Determine whether the keystroke is a number from the top of the keyboard.
if (e.KeyCode < Keys.D0 || e.KeyCode > Keys.D9)
{
// Determine whether the keystroke is a number from the keypad.
if (e.KeyCode < Keys.NumPad0 || e.KeyCode > Keys.NumPad9)
{
// Determine whether the keystroke is a backspace.
if(e.KeyCode != Keys.Back)
{
// A non-numerical keystroke was pressed.
// Set the flag to true and evaluate in KeyPress event.
nonNumberEntered = true;
}
}
}
}

// This event occurs after the KeyDown event and can be used to prevent
// characters from entering the control.
private void textBox1_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
// Check for the flag being set in the KeyDown event.
if (nonNumberEntered == true)
{
// Stop the character from being entered into the control since it is non-numerical.
e.Handled = true;
}
}