取消按键事件 [英] Cancel Key press event

问题描述

我怎样才能返回键，是说如果我想允许在文本框中只有整数值，我怎么能不允许用户在不进入其他的值，那么整数，对于，按键事件，我知道还有其他办法。如表达式的字符串值相匹配，但我想不分配无效值的文本框

How can I return the key, mean if I want to allow only integer value in the textbox , how can I don't allow user to not enter value other then integer, regarding, keypress event, I know there are other ways such as expression to match the string value, but I want to not assign invalid value to the textbox.

如果（（值> 0急症;及（价值< = 9））
，则分配
，否则
返回

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

推荐答案

使用Handled属性

Use the Handled Property

e.Handled = true;

$ b $从MSDN b

例如：链接

Example from MSDN: link

// 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;
    }
}

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