Subclassing and Hooking with Visual Basic

Caveats

Performance might be an issue when you use the WH_KEYBOARD and WH_KEYBOARD_LL hooks, especially with system-wide and low-level keyboard hooks. You should use these hooks judiciously.

The low-level keyboard hook forces every thread to receive messages from a single queue. This is how 16-bit Windows operating systems work. Therefore, the operating system cannot take advantage of multitasking. A problem that occurs in all 16-bit Windows operating systems can now occur in 32-bit Windows operating systems: a single application can hang all applications, even the desktop.

Because low-level keyboard hooks serialize all input to all windows, there is a large performance penalty. You should be careful when using hooks such as these. When you use these hooks, install them for as little time as possible.

Also, when using the WH_KEYBOARD_LL low-level keyboard hook, note that the debug hook cannot receive the input to this hook before the hook is called. The debug hook works normally with the keyboard hook (WH_KEYBOARD). Chapter 21 describes the debug hook.

When using Windows NT or Windows 2000 along with the enhanced Windows keyboards, note that the keys, which are duplicated on the left and right, now have different virtual key codes. Here is a list of left and right virtual key codes:

VK_LWIN and VK_RWIN

The left and right virtual key codes for the Windows keys

VK_LSHIFT and VK_RSHIFT

The left and right virtual key codes for the shift keys

VK_LCONTROL and VK_RCONTROL

The left and ...