Question

Can anyone explain why the check for Alt+Left Arrow key is triggered on a Alt+Right Arrow key press within the ProcessCmdKey method? When I originally coded this method, everything worked. I am beginning to question all my key handlers, but wanted to know if there was a good explaination or if I am missing something. All other key combinations work as expected.

Protected Overrides Function ProcessCmdKey(ByRef msg As Message, ByVal keyData As Keys) As Boolean
    If (keyData And Keys.Alt) = Keys.Alt Then
        If (keyData And Keys.Left) = Keys.Left Then
            'when Alt+Right key is pressed
            '   this executes, except when a breakpoint is set anywhere within this method
            '   this still executes in released code
            Debug.WriteLine("WTF!")
        End If
    End If
    Return MyBase.ProcessCmdKey(msg, keyData)
End Function

The work around is to check for the key press as If keyData = (Keys.Alt Or Keys.Left) Then

[update]
Ah, I got it. Thank you Mitch. I did check for that, but missed it.

? convert.ToString(Keys.Left, 2)
"100101"
? convert.ToString(Keys.Right,2)
"100111"

Still would like to know why hitting the breakpoint changes behavior.

[update]
Thank you again Mitch. Since it wasn’t reproducible for you, I suspect the solutions .suo file is corrupt. I deleted this file and now hitting the breakpoint has no affect.

Answer 1

Keys.Left  = 37 = 32 + 4     + 1
Keys.Right = 39 = 32 + 4 + 2 + 1

So bitwise, Keys.Right includes Key.Left. Therefore Anding with Keys.Left return True in either case.