Winform中Control.KeyDown 事件（整理自MSDN）

事件说明：

在控件有焦点的情况下按下键时发生（这里也没说是任意键，因为有些键在KeyDown中也是处理不了的）。

原型：

public event KeyEventHandler KeyDown

 

相关键事件按下列顺序发生：

1. KeyDown

2. KeyPress

3. KeyUp

注意：

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。某些键，如 Tab、Return、Esc 和箭头键，由控件自动处理。为使这些键引发 KeyDown 事件，必须在窗体上的每个控件中重写 IsInputKey 方法。用于重写 IsInputKey 的代码需要确定是否按下了某个特殊键，并且需要返回一个 true 值。

 

下面的代码示例使用 KeyDown 事件来确定输入到控件中的字符类型：

// 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;    }}

事件参数说明：

KeyEventArgs

为 KeyDown 或 KeyUp 事件提供数据。

参数说明：

KeyEventArgs（指定用户曾按下的键以及是否曾同时按下修改键：Ctrl、Alt 和 Shift 键）随着 KeyDown 或 KeyUp 事件的每一次发生而被传递。

当用户按下任意键时，发生 KeyDown 事件。当用户释放该键时，发生 KeyUp 事件。如果键被按住，那么，每次键重复时，KeyDown 事件都重复发生；但当用户释放该键时，仅发生一次 KeyUp 事件。

按下某个键时，还发生 KeyPress 事件。KeyPressEventArgs 随着 KeyPress 事件的每一次发生而被传递，并指定每次按键结果所形成的字符。

 

下面的代码示例演示如何检测按键的状态:

private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e){    // Determine whether the key entered is the F1 key. If it is, display Help.    if(e.KeyCode == Keys.F1 && (e.Alt || e.Control || e.Shift))    {        // Display a pop-up Help topic to assist the user.        Help.ShowPopup(textBox1, "Enter your name.", new Point(textBox1.Bottom, textBox1.Right));    }    else if(e.KeyCode == Keys.F2 && e.Modifiers == Keys.Alt)    {        // Display a pop-up Help topic to provide additional assistance to the user.        Help.ShowPopup(textBox1, "Enter your first name followed by your last name. Middle name is optional.",            new Point(textBox1.Top, this.textBox1.Left));    }}

 

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;    }}

只是拷贝了部分代码。

 

参数属性的说明：

KeyData 属性说明：

一个 Keys，表示按下的键的键代码以及修饰符标志（指示同时按下的 Ctrl、Shift 和 Alt 键的组合）。

可使用来自 Keys 的常数从 KeyData 属性提取信息。使用位 AND 运算符将由 KeyData 返回的数据与 Keys 中的常数进行比较，从而获得有关用户按下的键的信息。若要确定是否已按了特定的修改键，请使用 Control、Shift 和 Alt 属性。

KeyValue 属性说明：

KeyCode 属性的整数表示形式。