取消按键事件

Question

如何返回键值？也就是说，如果我想在文本框中只允许整数值，怎样可以防止用户输入非整数值呢？关于 KeyPress 事件，我知道还有其他方法可以匹配字符串值，但我想要的是不允许在文本框中输入无效的值。

if (( value >0 a&&(value <=9)) then 
    assigned
else 
    return

- Asim Sajjad

Answer 1

使用 Handled 属性。

e.Handled = true;

MSDN上的示例：链接

// 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;
            }
        }
    }
    //If shift key was pressed, it's not a number.
    if (Control.ModifierKeys == Keys.Shift) {
        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;
    }
}

- RvdK

Answer 2

您可以按照以下方式使用keypress事件。将e.Handled设置为true以取消用户输入。

    private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
    {
        if (!Char.IsDigit(e.KeyChar)) e.Handled = true;
    }

- m.zam

Answer 3

创建一个包含允许用户输入的字符的字符串。

使用 KeyDown 或 KeyUp 处理特殊键。

private void tbN1_KeyPress(object sender, KeyPressEventArgs e)
{
    String sKeys = "1234567890ABCDEF";
    if (!sKeys.Contains(e.KeyChar.ToString().ToUpper()))
        e.Handled = true;
}

- MrCris

Answer 4

从技术上讲，这是错误的，因为您标记了您的问题WPF。但是，既然您接受了其他Windows Forms答案，我将发布我的解决方案，该解决方案适用于实数而非整数。它还本地化为仅接受当前语言环境的小数分隔符。

private void doubleTextBox_KeyPress (object sender, KeyPressEventArgs e)
{
  var textBox = sender as TextBoxBase;
  if (textBox == null)
      return;

  // did the user press their locale's decimal separator?
  if (e.KeyChar.ToString() == CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator)
  {
      if (textBox.Text.Length == 0) // if empty, prefix the decimal with a 0
      {
          textBox.Text = "0" + CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator;
          e.Handled = true;
          textBox.SelectionStart = textBox.TextLength;
      }
      // ignore extra decimal separators
      else if (textBox.Text.Contains(CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator))
          e.Handled = true;
  }
  // allow backspaces, but no other non-numeric characters;
  // note that arrow keys, delete, home, end, etc. do not trigger KeyPress
  else if (e.KeyChar != '\b' && (e.KeyChar < '0' || e.KeyChar > '9'))
      e.Handled = true;
}

- Matt Chambers

Answer 5

对于WPF，使用类似以下代码的PreviewTextInput事件：

// Filter out non-numeric keys.
private void MyApp_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
String sKeys = "1234567890";
if (!sKeys.Contains(e.Text))
    e.Handled = true;
}

- Skyfish

Answer 6

你可以继承自TextBox，然后：

Protected Overrides Sub OnTextInput(ByVal e As System.Windows.Input.TextCompositionEventArgs)

        Dim newChar As Char = Convert.ToChar(e.Text)
        If Not [Char].IsDigit(newChar) Then e.Handled = True

End Sub

C# 版本

protected override void OnTextInput(System.Windows.Input.TextCompositionEventArgs e)
{    
    char newChar = Convert.ToChar(e.Text);        
    if (!Char.IsDigit(newChar)) e.Handled = true; 
}

- Drake

Answer 7

你可以使用 MaskedTextBox 并强制其仅接受整数。

- MadBoy

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对于WPF，您可能需要参考这个页面：https://dev59.com/sXRB5IYBdhLWcg3w4bAo - Vlad