文本框中只能接受數字，其他字符不予處理

今天回覆了一個類似的帖子，這也是我剛剛學習C#的時候想要解決的一個問題，當初想寫一個“家庭小賬本”，可是，怎麼弄都不能實現，總是在KeyDown（）事件中判斷出了輸入的是非數字字符，卻無法阻止文本框接受這個輸入，非數字字符還是顯示出來了。

首先：我還是在VS2003中重複了剛纔的問題

1、添加了一個Windows窗體Form1，在Form1中添加了一個文本框textBox1
2、在textBox1的KeyDown()事件中加入了以下代碼：
private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
 if ( e.KeyValue < 48 && e.KeyValue >57 ) //如果輸入的字符是從 ‘0’ 到 ‘9’
 {
       //什麼都不做
 }
 else
 {
  e.Handled=true; //如果輸入的是非數字字符，則提前將這個事件結束掉，而不添加
  MessageBox.Show( e.Handled.ToString() ）；
 }
}

沒寫完，待續...

MSDN上的例子http://msdn.microsoft.com/library/chs/default.asp?url=/library/CHS/cpref/html/frlrfsystemwindowsformscontrolclasskeydowntopic.asp

[C#] <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

         // 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;

              }

         }