Ensure statement is executed only once when a key is pressed and held.

问题

If you press and hold the 5 key on the numpad it will continue to execute a statement in the KeyDown event handler. How can i ensure the statement is executed only once, even if i hold the key down?

Thanks for your attention.

private void form_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
   if (e.KeyCode == Keys.NumPad5)
   {
        dados.enviar("f"); //I want this to run only once!
   }
}

回答1:

You can set flag on key down and reset it on key up.

    private bool isPressed = false;
    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_KeyDown(object sender, KeyEventArgs e)
    {
        if(e.KeyCode == Keys.B && !isPressed )
        {
            isPressed = true;
            // do work
        }
    }

    private void Form1_KeyUp(object sender, KeyEventArgs e)
    {
        if (isPressed )
            isPressed = false;
    }

回答2:

bool alreadyPressed = false;
...

if (e.KeyCode == Keys.NumPad5 && ! alreadyPressed)
{
    alreadyPressed = true;
    ...

来源：https://stackoverflow.com/questions/9251522/ensure-statement-is-executed-only-once-when-a-key-is-pressed-and-held