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Autohighlight active control (MDI Form)

This is a very simple and useful solution to highlight input controls without writting a function for each control. Only include a module with the code shown below (rename MDIFORM with your MDIForm) and call SetHook at the MDIForm_Load function and and Unhook at the MDIForm_QueryUnload function. Please vote, if you think its a good solution.

Side Effects
When running this progam in the IDE do not use the STOP-Button to exit the program, because the unhook function will not be executed and the IDE crashes!!!

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(5(5 Vote))

Option Explicit
' USER32 functions
Private Declare Function SetWindowsHookEx Lib "user32" Alias "SetWindowsHookExA" _
 (ByVal idHook As Long, ByVal lpfn As Long, ByVal hmod As Long, ByVal dwThreadId As Long) As Long
Private Declare Function CallNextHookEx Lib "user32" _
 (ByVal hHook As Long, ByVal ncode As Long, ByVal wParam As Long, lParam As Any) As Long
Private Declare Function UnhookWindowsHookEx Lib "user32" (ByVal hHook As Long) As Long
' KERNEL32 functions
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
 (hpvDest As Any, hpvSource As Any, ByVal cbCopy As Long)
' CONSTANTS
Private Const WH_CALLWNDPROC = 4
Public Const WM_SETFOCUS = &H7
Public Const WM_KILLFOCUS = &H8
' STRUCTS
Private Type CWPSTRUCT
 lParam As Long
 wParam As Long
 message As Long
 hwnd As Long
End Type
' REST
Public hHook As Long
'
Public Function SetHook()
If Not hHook Then
 hHook = SetWindowsHookEx(WH_CALLWNDPROC, AddressOf WndProc, App.hInstance, App.ThreadID)
End If
End Function
'
Private Function WndProc(ByVal idHook As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Dim CWP As CWPSTRUCT
Dim C As Control
On Local Error Resume Next
CopyMemory CWP, ByVal lParam, Len(CWP)
WndProc = CallNextHookEx(hHook, idHook, wParam, ByVal lParam)
Select Case CWP.message
Case WM_SETFOCUS, WM_KILLFOCUS
  For Each C In MDIFORM.ActiveForm.Controls
  Err.Clear
  If CWP.hwnd = C.hwnd Then
   If Err.Number = 0 Then
    If CWP.message = WM_SETFOCUS Then
     If (TypeOf C Is TextBox) Or _
      (TypeOf C Is ComboBox) Then
      C.BackColor = &H80000018
     End If
    Else
     If (TypeOf C Is TextBox) Or _
      (TypeOf C Is ComboBox) Then
      C.BackColor = &H80000005
     End If
    End If
    Exit For
   End If
  End If
  Next
End Select
End Function
'
Public Function UnHook()
If hHook Then
 UnhookWindowsHookEx hHook
End If
End Function