Control.KeyDown 事件

定义

命名空间:

System.Windows.Forms

程序集:

System.Windows.Forms.dll

Source:

Control.cs

在控件有焦点的情况下按下键时发生。

C#

public event System.Windows.Forms.KeyEventHandler? KeyDown;

事件类型

KeyEventHandler

示例

下面的代码示例使用 KeyDown 事件来确定在 控件中输入的字符的类型。

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;
            }
        }
    }
    //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)
    {
        // Stop the character from being entered into the control since it is non-numerical.
        e.Handled = true;
    }
}

下面的代码示例演示了引发 KeyDown、 、 KeyUpKeyPress 事件的顺序，以及如何在它们上注册事件处理程序。

C#

public partial class Form2 : Form
{
    public Form2()
    {
        InitializeComponent();
        textBox2.Multiline = true;
        textBox2.ScrollBars = ScrollBars.Both;

        //Setup events that listens on keypress
        textBox1.KeyDown += TextBox1_KeyDown;
        textBox1.KeyPress += TextBox1_KeyPress;
        textBox1.KeyUp += TextBox1_KeyUp;
    }

    // Handle the KeyUp event to print the type of character entered into the control.
    private void TextBox1_KeyUp(object sender, KeyEventArgs e)
    {
        textBox2.AppendText( $"KeyUp code: {e.KeyCode}, value: {e.KeyValue}, modifiers: {e.Modifiers}" + "\r\n");
    }

    // Handle the KeyPress event to print the type of character entered into the control.
    private void TextBox1_KeyPress(object sender, KeyPressEventArgs e)
    {
        textBox2.AppendText( $"KeyPress keychar: {e.KeyChar}" + "\r\n");
    }

    // Handle the KeyDown event to print the type of character entered into the control.
    private void TextBox1_KeyDown(object sender, KeyEventArgs e)
    {
        textBox2.AppendText( $"KeyDown code: {e.KeyCode}, value: {e.KeyValue}, modifiers: {e.Modifiers}" + "\r\n");
    }
}

注解

关键事件按以下顺序发生：

1. KeyDown

2. KeyPress

3. KeyUp

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，请将窗体的事件KeyPress处理方法中的 属性设置为 。KeyPressEventArgs.Handledtrue 某些键（如 TAB、RETURN、ESC 和箭头键）由控件自动处理。 若要让这些键引发 KeyDown 事件，必须覆盖 IsInputKey 窗体上每个控件中的 方法。 替代 的代码 IsInputKey 需要确定是否按下了一个特殊键并返回值 true。 可以处理 PreviewKeyDown 事件并将 属性设置为 IsInputKeytrue，而不是重写 IsInputKey 方法。 有关代码示例，请参阅 PreviewKeyDown 事件。

有关处理事件的详细信息，请参阅 处理和引发事件。

适用于

另请参阅

• KeyEventArgs
• KeyEventHandler
• OnKeyDown(KeyEventArgs)
• KeyUp
• KeyPress
• PreviewKeyDown