C# Keys Enumeration Confused: Keys.Alt or Keys.RButton | Keys.ShiftKey | Keys.Alt

Question

I was trying to test whether the Alt key was pressed.

I had a check similar to:

private void ProcessCmdKey(Keys keyData)
{
 if (keyData == Keys.Alt)
 {
  System.Console.WriteLine ("Alt Key Pressed");
 } 
}

Anyways needless to say when I breakpointed when I had pressed the Alt key the debugger told me the key that was pressed was actually Keys.RButton | Keys.ShiftKey | Keys.Alt

Can anyone shed some light on what is going on or perhaps point me to an article that can explain?

Thanks FZ

Edit: I am still a bit lost as to why the ENUM would have have other bit values set and not simply the Alt key? I understand that the enum can include more than 1 state with the flags attrivbute but I am not sure why it does if all I pressed was Alt?

Answer 1

If you want to test whether Alt is part of the pressed keys, you can perform a bitwise test;

if((keyData & Keys.Alt) == Keys.Alt) {...}

Answer 2

Keys is a Flags Enumeration. This means it can have more than one value at a given time. You should check it like so:

if ( (keyData & Keys.Alt) == Keys.Alt)
{
   // Alt was pressed!
}

Answer 3

Enum with FlagsAttribute are implemented using bits.
See this link for a good start - http://msdn.microsoft.com/en-us/library/cc138362.aspx

EDIT: Are you pressing RIGHT (mouse button) with Shift key during the operation, to select/highlight something, while debugging?