This is named "struct" to be consistent with the Windows API name, but it is defined as a class since it is passed as a pointer (AKA reference) in SetWindowsHookEx and CallNextHookEx. Or it can be defined as a struct and passed with ref (ByRef in VB.NET).

///     SetWindowsHookEx can be used to inject a DLL into another process. A 32-bit DLL cannot be injected into a

///     of hooks in other processes, it is required that a 32-bit application call SetWindowsHookEx to inject a 32-bit

///     DLL into 32-bit processes, and a 64-bit application call SetWindowsHookEx to inject a 64-bit DLL into 64-bit

///     context; specifically, on the thread that called SetWindowsHookEx. This means that the hooking application must

static extern IntPtr SetWindowsHookEx(HookType hookType, HookProc lpfn, IntPtr hMod, uint dwThreadId);

Private Shared Function SetWindowsHookEx(ByVal hookType As HookType, ByVal lpfn As HookProc, ByVal hMod As IntPtr, ByVal dwThreadId As UInteger) As IntPtr

    hHook = SetWindowsHookEx(HookType.WH_KEYBOARD_LL, hook, hModule, 0);

Remember to call UnhookWindowsHookEx using the handle returned by SetWindowsHookEx

     SetWindowsHookEx(HookType.WH_KEYBOARD, this.myCallbackDelegate, IntPtr.Zero, AppDomain.GetCurrentThreadId());

     protected static extern IntPtr SetWindowsHookEx(HookType code, HookProc func, IntPtr hInstance, int threadID);

    SetWindowsHookEx(HookType.WH_KEYBOARD, Me.myCallbackDelegate, IntPtr.Zero, AppDomain.GetCurrentThreadId())

    Friend Shared Function SetWindowsHookEx(ByVal idHook As Integer, ByVal lpfn As HookProc, ByVal hInstance As IntPtr, ByVal threadId As Integer) As Integer

[SetWindowsHookEx] on MSDN

///     Removes a hook procedure installed in a hook chain by the SetWindowsHookEx function.

///     handle obtained by a previous call to <see cref="SetWindowsHookEx" />.

See SetWindowsHookEx, CallNextHookEx