How to: Determine Which Modifier Key Was Pressed
When you create an application that accepts the user's keystrokes, you may also want to monitor for modifier keys such as the SHIFT, ALT, and CTRL keys. When a modifier key is pressed in combination with other keys, or with mouse clicks, your application can respond appropriately. For example, if the letter S is pressed, this may simply cause an "s" to appear on the screen, but if the keys CTRL+S are pressed, the current document may be saved. If you handle theevent, the property of the received by the event handler specifies which modifier keys are pressed. Alternatively, the property of KeyEventArgs specifies the character that was pressed as well as any modifier keys combined with a bitwise OR. However, if you are handling the event or a mouse event, the event handler does not receive this information. In this case, you must use the property of the class. In either case, you must perform a bitwise AND of the appropriate value and the value you are testing. The Keys enumeration offers variations of each modifier key, so it is important that you perform the bitwise AND with the correct value. For example, the SHIFT key is represented by , , and The correct value to test SHIFT as a modifier key is Shift. Similarly, to test for CTLR and ALT as modifiers you should use the and values, respectively.
Visual Basic programmers can also access key information through theproperty. For more information, see
To determine which modifier key was pressed
Use the bitwise AND operator with the ModifierKeys property and a value of the Keys enumeration to determine whether a particular modifier key is pressed. The following code example shows how to determine whether the SHIFT key is pressed within a KeyPress event handler.