TOPIC:

USING System.Runtime.InteropServices // put this at the top of the prg file

...

// The delegate needs to have the same parameters and return type as the function/method to be associated with
DELEGATE EnumChildWindows_Delegate(hWnd AS PTR, lParam AS DWORD ) AS LOGIC 

...

METHOD GetAllControls()
	LOCAL ___aControls := {} AS ARRAY

	LOCAL oArrayHandle AS GCHandle
	oArrayHandle := GCHandle.Alloc( ___aControls ) // create a handle to the managed object (array)
		
	LOCAL oEnumDelegate AS EnumChildWindows_Delegate
	oEnumDelegate := __GetCtrl // instantiate the delegate (managed function pointer) to our callback function

	LOCAL hWnd AS PTR
	hWnd := oSurface:Handle()

	// pass to EnumChildWindows() a managed pointer (via the delegate) to the 
	// callback function and the handle of the array as a pointer:
	EnumChildWindows(hWnd , Marshal.GetFunctionPointerForDelegate( oEnumDelegate ), GCHandle.ToIntPtr( oArrayHandle ) )
		
	// we don't need it anymore, release memory
	oArrayHandle:Free()
	// make sure the delegate is not collected by the GC, while it is still 
	// being used by the win32 code of EnumChildWindows(), before we reach here
	GC.KeepAlive( oEnumDelegate )
RETURN ___aControls

...

FUNC __GetCtrl(hWnd AS PTR, lParam AS DWORD ) AS LOGIC
	LOCAL oArrayHandle AS GCHandle
	oArrayHandle := GCHandle.FromIntPtr( (IntPtr) lParam ) // retrieve back the handle to the array

	LOCAL aControls AS ARRAY
	aControls := (ARRAY) oArrayHandle:Target // retrieve the original array object
	
	LOCAL oObj AS USUAL
	oObj := GetObjectByHandle( hWnd )
	IF oObj != null_object
		AAdd( aControls, oObj )
	ENDIF
RETURN TRUE

METHOD ShowControls()
LOCAL a AS ARRAY
LOCAL i AS DWORD  	
	
	a := SELF:GetAllControls()  // John's method	
	
	? ALen ( a )
	
	FOR i := 1 TO ALen ( a )
		
		? a[i]
		
	NEXT
	
	?
	? 
	
	a := SELF:GetAllChildren() // existing VO method	
	
	? ALen ( a )
	
	FOR i := 1 TO ALen ( a )
		
		? a[i]
		
	NEXT

	RETURN SELF