通过

Control.KeyPress 事件

  • 项目

在控件有焦点的情况下按下键时发生。

**命名空间:**System.Windows.Forms
**程序集:**System.Windows.Forms（在 system.windows.forms.dll 中）

语法

声明
Public Event KeyPress As KeyPressEventHandler
用法
Dim instance As Control
Dim handler As KeyPressEventHandler

AddHandler instance.KeyPress, handler

public event KeyPressEventHandler KeyPress

public:
event KeyPressEventHandler^ KeyPress {
    void add (KeyPressEventHandler^ value);
    void remove (KeyPressEventHandler^ value);
}

/** @event */
public void add_KeyPress (KeyPressEventHandler value)

/** @event */
public void remove_KeyPress (KeyPressEventHandler value)

JScript 支持使用事件，但不支持进行新的声明。

备注

键事件按下列顺序发生：

  1. KeyDown

  2. KeyPress

  3. KeyUp

非字符键不会引发 KeyPress 事件；但非字符键却可以引发 KeyDown 和 KeyUp 事件。

使用 KeyChar 属性在运行时对键击进行取样，并且使用或修改公共键击的子集。

若要仅在窗体级别处理键盘事件而不允许其他控件接收键盘事件，请将窗体的 KeyPress 事件处理方法中的 KeyPressEventArgs.Handled 属性设置为 true。

有关处理事件的更多信息，请参见 使用事件。

示例

下面的代码示例使用 KeyPress 事件来禁止向控件输入字符。

    ' Boolean flag used to determine when a character other than a number is entered.
    Private nonNumberEntered As Boolean = False
   
   
    ' Handle the KeyDown event to determine the type of character entered into the control.
    Private Sub textBox1_KeyDown(sender As Object, e As System.Windows.Forms.KeyEventArgs) _
         Handles textBox1.KeyDown
        ' 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 OrElse e.KeyCode > Keys.D9 Then
            ' Determine whether the keystroke is a number from the keypad.
            If e.KeyCode < Keys.NumPad0 OrElse e.KeyCode > Keys.NumPad9 Then
                ' Determine whether the keystroke is a backspace.
                If e.KeyCode <> Keys.Back Then
                    ' A non-numerical keystroke was pressed. 
                    ' Set the flag to true and evaluate in KeyPress event.
                    nonNumberEntered = True
                End If
            End If
        End If
    End Sub 'textBox1_KeyDown
   
   
    ' This event occurs after the KeyDown event and can be used 
    ' to prevent characters from entering the control.
    Private Sub textBox1_KeyPress(sender As Object, e As System.Windows.Forms.KeyPressEventArgs) _
        Handles textBox1.KeyPress
        ' Check for the flag being set in the KeyDown event.
        If nonNumberEntered = True Then
            ' Stop the character from being entered into the control since it is non-numerical.
            e.Handled = True
        End If
    End Sub 'textBox1_KeyPress
End Class 'Form1 

// 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;
    }
}

   // Boolean flag used to determine when a character other than a number is entered.
private:
   bool nonNumberEntered;

   // Handle the KeyDown event to determine the type of character entered into the control.
   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.
   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;
      }
   }

// Boolean flag used to determine when a character other than a number 
// is entered.
private boolean 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.get_KeyCode().CompareTo(Keys.D0)) < 0 
        || (e.get_KeyCode().CompareTo(Keys.D9) > 0)) {

        // Determine whether the keystroke is a number from the keypad.
        if ((e.get_KeyCode().CompareTo(Keys.NumPad0) < 0 
            || (e.get_KeyCode().CompareTo(Keys.NumPad9)) > 0)) {

            // Determine whether the keystroke is a backspace.
            if (!(e.get_KeyCode().Equals(Keys.Back))) {
                    // A non-numerical keystroke was pressed.
                    // Set the flag to true and evaluate in KeyPress event.
                    nonNumberEntered = true;
            }
        }
    }
} //textBox1_KeyDown

// 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.set_Handled(true);
    }
} //textBox1_KeyPress

平台

Windows 98、Windows 2000 SP4、Windows CE、Windows Millennium Edition、Windows Mobile for Pocket PC、Windows Mobile for Smartphone、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition

.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。

版本信息

.NET Framework

受以下版本支持：2.0、1.1、1.0

.NET Compact Framework

受以下版本支持：2.0、1.0

请参见

参考

Control 类
Control 成员
System.Windows.Forms 命名空间
KeyChar
OnKeyPress
IsInputChar
KeyUp
Control.KeyDown 事件