Control.KeyDown 事件

定義

命名空間:

System.Windows.Forms

組件:

System.Windows.Forms.dll

來源:

Control.cs

發生於按下按鍵且焦點在控制項時。

C#

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

事件類型

KeyEventHandler

範例

下列程式碼範例會 KeyDown 使用 事件來判斷輸入控制項中的字元類型。

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;
    }
}

下列程式碼範例示範引發 KeyDown 、 KeyUpKeyPress 、事件，以及如何在它們上註冊事件處理常式的順序。

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");
    }
}

備註

主要事件會依下列順序發生：

1. KeyDown

2. KeyPress

3. KeyUp

若只要在表單層級處理鍵盤事件，且無法讓其他控制項接收鍵盤事件，請將 KeyPressEventArgs.Handled 表單 KeyPress 事件處理方法中的 屬性設定為 true 。 控制項會自動處理某些索引鍵，例如 TAB、RETURN、ESC 和方向鍵。 若要讓這些索引鍵引發 KeyDown 事件，您必須覆寫 IsInputKey 表單上每個控制項中的 方法。 覆寫 IsInputKey 的程式碼必須判斷是否按下其中一個特殊按鍵，並傳回 的值 true 。 您可以處理 事件， PreviewKeyDown 並將 屬性設定 IsInputKey 為 true ，而不是覆 IsInputKey 寫 方法。 如需程式碼範例，請參閱 PreviewKeyDown 事件。

如需處理事件的詳細資訊，請參閱 處理和引發事件。

適用於

另請參閱

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