C# – Basic WinForm KeyDown event handling

cevent handlingkeydownwinforms

I'm using WinForms. I've created an event handler for the KeyDown event of the main form, thereby invoking a button's Click event handler.

The Click event handler called is dependent upon the specific key pressed. If a user clicks the button rather than using the key, and then subsequently tries to use the key thereafter, the key (down arrow for example) acts as a tab-cycle, changing focus between each button control on the form (rather than executing the Keydown handler).

Any ideas ?

Best Answer

The problem is, the button has the focus when it is clicked, so subsequent key presses are not caught by the form itself, but by the buttons instead. In the click event handler for the buttons, focus the form:

this.Focus();

That way, focus is restored to the form so the form will listen for the keypress events.

Edit

The real problem, as you have discovered, is that arrow keys are not treated as input keys. To fix this, you need to create a new class that inherits whatever control you want to use. Then, you override the IsInputKey method to treat arrow keys as input keys. Check this link: http://bytes.com/topic/c-sharp/answers/517530-trapping-arrow-keys-usercontrol. This article is also useful: http://msdn.microsoft.com/en-us/library/system.windows.forms.control.isinputkey.aspx.

Related Solutions

C# trying to capture the KeyDown event on a form

Have you set the KeyPreview property of the form to true? That will cause the form to get a "first look" at key events.

Update: getting this to work properly when a Button has focus seems to be a bit tricky. The Button control intercepts the arrow key presses and moves focus to the next or previous control in the tab order in a manner so that the KeyDown, KeyUp and KeyPress events are not raised. However, the PreviewKeyDown event is raised, so that can be used:

private void Form_KeyDown(object sender, KeyEventArgs e)
{
    e.Handled = ProcessKeyDown(e.KeyCode);
}

// event handler for the PreViewKeyDown event for the buttons
private void ArrowButton_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e)
{
    ProcessKeyDown(e.KeyCode);

}

private bool ProcessKeyDown(Keys keyCode)
{
    switch (keyCode)
    {
        case Keys.Up:
            {
                // act on up arrow
                return true;
            }
        case Keys.Down:
            {
                // act on down arrow
                return true;
            }
        case Keys.Left:
            {
                // act on left arrow
                return true;
            }
        case Keys.Right:
            {
                // act on right arrow
                return true;
            }
    }
    return false;
}

Still, the focus moves around in a rather ugly manner...

C# – Up, Down, Left and Right arrow keys do not trigger KeyDown event

I was having the exact same problem. I considered the answer @Snarfblam provided; however, if you read the documentation on MSDN, the ProcessCMDKey method is meant to override key events for menu items in an application.

I recently stumbled across this article from microsoft, which looks quite promising: http://msdn.microsoft.com/en-us/library/system.windows.forms.control.previewkeydown.aspx. According to microsoft, the best thing to do is set e.IsInputKey=true; in the PreviewKeyDown event after detecting the arrow keys. Doing so will fire the KeyDown event.

This worked quite well for me and was less hack-ish than overriding the ProcessCMDKey.

Best Answer

Related Solutions

C# trying to capture the KeyDown event on a form

C# – Up, Down, Left and Right arrow keys do not trigger KeyDown event

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