KeyDown recognizes the left and right directional arrow keys, but not up and down

问题

With the code below, the Left and Right arrow keys function as expected, but the up and down arrows are not recognized (stepping through it, the first two conditions are met where appropriate, but the second two never are):

private void textBox1_KeyDown(object sender, KeyEventArgs e) {
    TextBox tb = (TextBox)sender;

    if (e.KeyCode.Equals(Keys.Left)) {
        SetFocusOneColumnBack(tb.Name);
        e.Handled = true;
        return;
    }
    if (e.KeyCode.Equals(Keys.Right)) {
        SetFocusOneColumnForward(tb.Name);
        e.Handled = true;
        return;
    }
    if (e.KeyCode.Equals(Keys.Up)) {
        SetFocusOneRowUp(tb.Name);
        e.Handled = true;
        return;
    }
    if (e.KeyCode.Equals(Keys.Down)) {
        SetFocusOneRowDown(tb.Name);
        e.Handled = true;
        return;
    }
}

Why would this be, and how can I fix it?

UPDATE

Here's what I see when I hover over e.Keycode while stepping through. If I pressed

...Left arrow key, I see: e.KeyCode = "LButton | MButton | Space"
...Right arrow key, I see: e.KeyCode = "LButton | RButton | MButton | Space"
...Up arrow key, I see: e.KeyCode = "RButton | MButton | Space"
...Down arrow key, I see: e.KeyCode = "Backspace | Space"

This has got me baffled (what it's showing me), but on keyleft and keyright, my code is entered - it never is for keyup and keydown, no matter how hard I clench my teeth.

回答1:

Windows captures certain keys for UI navigation before they every get sent to your form. If you want to override this behavior you need to overload the IsInputKey method (and subclass the text field):

    protected override bool IsInputKey(Keys keyData)
    {
        if (keyData == Keys.Right)
            return true;
        return base.IsInputKey(keyData);
    }

回答2:

I find that using the PreviewKeyDown does work (I had to remove the "e.Handled = true" code, as it doesn't apply in the PreviewKeyDown event):

private void textBoxQH1_PreviewKeyDown(object sender,   PreviewKeyDownEventArgs e) {
    TextBox tb = (TextBox)sender;

    if (e.KeyCode.Equals(Keys.Up)) {
        SetFocusOneRowUp(tb.Name);
        return;
    }
    if (e.KeyCode.Equals(Keys.Down)) {
        SetFocusOneRowDown(tb.Name);
        return;
    }
}

So, three different events were needed to handle the various keys I was looking for: KeyPress for regular characters, KeyDown for non-characters (left and right arrow keys) and this one (PreviewKeyDown) for the up and down arrow keys.

回答3:

You can use this code:

private void TextBox1_KeyDown(object sender, KeyEventArgs e)
{
    switch (e.KeyCode)
    {
        case Keys.Up:
            //Do stuff
            break;
        case Keys.Down:
            //Do stuff
            break;
        case Keys.Left:
            //Do stuff
            break;
        case Keys.Right:
            //Do stuff
            break;
    }
}

回答4:

Well too late for the party but if anyone is interested, use e.KeyValue instead, as an example, e.KeyValue for left arrow key is 37 and for right arrow key 39 and so on.

来源：https://stackoverflow.com/questions/10520472/keydown-recognizes-the-left-and-right-directional-arrow-keys-but-not-up-and-dow

标签

winforms

keydown

keycode

arrow-keys