[RESOLVED] IntPtr vs HandleRef

Hello all,
I'm making a wrapper DLL for my Windows API functions that I use a lot. Now anyone who has worked with windows API knows that probably 80% of the windows API calls use one or more handles as argument(s). Now I've read that sometimes GC will collect the IntPtr and then your PInvoke will fail.
I've got a few questions.

#1 Why/when use HandleRef Over IntPtr
#2 What is the correct method of declaring a HandleRef ( what is the wrapper ?)

And I have a few other questions.
#3 You can import a external function using the DLLImport Attribute or using a 'Declare' and 'lib' Which one is the best/correct ? (to me the DLLImport attribute looks so much more legit than the 'declare' and 'lib')
#4 I Want to create a Wrapper for SendMessage But It can have various return data types (and probably various argument datatypes) Is it correct If I just make the return type Object ? Or would I need to make a class just for SendMessage ?

EDIT #5 What is the difference between Intptr and a normal Integer ? it seems like they both just contain numeric data ?

1. HandleRef is not really an alternative to an IntPtr. A HandleRef itself contains an IntPtr, as well as a managed reference to the object that that IntPtr refers to. As the documentation says, you would use a HandleRef when that object is not referenced anywhere else in managed code. If there are no references to a managed object then that object is eligible for garbage collection, so a HandleRef exists simply to create a managed reference, thus preventing the object being garbage collected.
2. You invoke the constructor with the New keyword, just as you do with a class, and pass the object and the IntPtr.
3. 'Declare' is a VB6 holdover. DllImport is the .NET way to call an unmanaged function.
4. For the different parameter types, you should overload the method. For the different return types, you could just declare a single method with return type Object, but I would tend to declare multiple methods with different names and return types as appropriate.
5. An IntPtr is specifically intended to store a value that represents a handle or a pointer, while an Integer stores things like counts, etc. You would never, for example, multiply two IntPtrs together. You could use Integers all the time but it's a metter of intent.

At some point however a function only allows a HandleRef as a parameter and not the IntPtr. Just go with IntPtr as long the parameters work, and as soon the GetLastError returns a "invalid parameter" error you might have to use a HandleRef instead.

Since API's don't continue until the function completed, a handleref is usually useless. A few functions that require a handleref:

Code:

---

    <Runtime.InteropServices.DllImport("user32.dll", EntryPoint:="GetWindowLong")> _
    Private Shared Function GetWindowLongPtr32(ByVal hWnd As Runtime.InteropServices.HandleRef, ByVal nIndex As Integer) As Long
    End Function
    <Runtime.InteropServices.DllImport("user32.dll", EntryPoint:="GetWindowLongPtr")> _
    Private Shared Function GetWindowLongPtr64(ByVal hWnd As Runtime.InteropServices.HandleRef, ByVal nIndex As Integer) As Long
    End Function
    Private Declare Function GetWindowRect Lib "user32" (ByVal hWnd As System.Runtime.InteropServices.HandleRef, ByRef lpRect As API.WRECT) As Boolean
    Private Declare Function GetClientRect Lib "user32" (ByVal hWnd As System.Runtime.InteropServices.HandleRef, ByRef lpRect As API.WRECT) As Boolean

---

Thank you very much for the replies :)
I was thinking about sendmessage.
Would it work if I created a class(of returntype)

like

Code:

---

Class SendMessage(Of returntype)

    Function sendmessage(...) As returntype

    End Function

End Class

---

Assuming that Function SendMessage is the wrapper to the Windows API ?

Sure it would work, but there are ALOT of messages. There are WM_ messages, but also for buttons, textboxes, checkboxes, radiobuttons, listview, listboxes, pictureboxes, alot. If you were to change all these messages to functions/subs, it would become an ENORMOUS class.

I recommend storing all these messages in an enumeration and keep all regular non-argument messages in a single function, and the more argument heavy functions (get text) in a separate one.

I added all functions in the start, but the message list is simply too large. I did make separate structures for the SendKey commands though.

vb Code:

Public Class WM
        Public Enum SC 'System Commands
            CLOSE = &HF060
            CONTEXTHELP = &HF180
            CDEFAULT = &HF160
            HOTKEY = &HF150
            HSCROLL = &HF080
            ISSECURE = &H1
            KEYMENU = &HF100
            MAXIMIZE = &HF030
            MINIMIZE = &HF020
            MONITORPOWER = &HF170
            MouseMenu = &HF090
            MOVE = &HF010
            NEXTWINDOW = &HF040
            PREVWINDOW = &HF050
            RESTORE = &HF120
            SCREENSAVE = &HF140
            Size = &HF000
            TASKLIST = &HF130
            VSCROLL = &HF070
        End Enum
 
        Public Enum msg As UInteger
            USER = &H400&
            ACTIVATE = &H6
            ACTIVATEAPP = &H1C
            ASKCBFORMATNAME = &H30C
            CANCELJOURNAL = &H4B
            CANCELMODE = &H1F
            CHANGECBCHAIN = &H30D
            Chr = &H102
            CHARTOITEM = &H2F
            CHILDACTIVATE = &H22
            CHOOSEFONT_GETLOGFONT = (USER + 1)
            CHOOSEFONT_SETFLAGS = (USER + 102)
            CHOOSEFONT_SETLOGFONT = (USER + 101)
            CLEAR = &H303
            CLOSE = &H10
            Command = &H111
            COMMNOTIFY = &H44 ' no longer suported
            COMPACTING = &H41
            COMPAREITEM = &H39
            CONVERTREQUESTEX = &H108
            Copy = &H301
            COPYDATA = &H4A
            CREATE = &H1
            CTLCOLORBTN = &H135
            CTLCOLORDLG = &H136
            CTLCOLOREDIT = &H133
            CTLCOLORLISTBOX = &H134
            CTLCOLORMSGBOX = &H132
            CTLCOLORSCROLLBAR = &H137
            CTLCOLORSTATIC = &H138
            CUT = &H300
            DDE_FIRST = &H3E0
            DDE_ACK = (DDE_FIRST + 4)
            DDE_ADVISE = (DDE_FIRST + 2)
            DDE_DATA = (DDE_FIRST + 5)
            DDE_EXECUTE = (DDE_FIRST + 8)
            DDE_INITIATE = (DDE_FIRST)
            DDE_LAST = (DDE_FIRST + 8)
            DDE_POKE = (DDE_FIRST + 7)
            DDE_REQUEST = (DDE_FIRST + 6)
            DDE_TERMINATE = (DDE_FIRST + 1)
            DDE_UNADVISE = (DDE_FIRST + 3)
            DEADCHAR = &H103
            DELETEITEM = &H2D
            DESTROY = &H2
            DESTROYCLIPBOARD = &H307
            DEVMODECHANGE = &H1B
            DRAWCLIPBOARD = &H308
            DRAWITEM = &H2B
            DROPFILES = &H233
            ENABLE = &HA
            ENDSESSION = &H16
            ENTERIDLE = &H121
            ENTERMENULOOP = &H211
            ERASEBKGND = &H14
            EXITMENULOOP = &H212
            FONTCHANGE = &H1D
            GETFONT = &H31
            GETDLGCODE = &H87
            GETHOTKEY = &H33
            GETMINMAXINFO = &H24
            GETTEXT = &HD
            GETTEXTLENGTH = &HE
            HOTKEY = &H312
            HSCROLL = &H114
            HSCROLLCLIPBOARD = &H30E
            ICONERASEBKGND = &H27
            IME_CHAR = &H286
            IME_COMPOSITION = &H10F
            IME_COMPOSITIONFULL = &H284
            IME_CONTROL = &H283
            IME_ENDCOMPOSITION = &H10E
            IME_KEYDOWN = &H290
            IME_KEYLAST = &H10F
            IME_KEYUP = &H291
            IME_NOTIFY = &H282
            IME_SELECT = &H285
            IME_SETCONTEXT = &H281
            IME_STARTCOMPOSITION = &H10D
            INITDIALOG = &H110
            INITMENU = &H116
            INITMENUPOPUP = &H117
            KEYDOWN = &H100
            KEYFIRST = &H100
            KEYLAST = &H108
            KEYUP = &H101
            KILLFOCUS = &H8
            LBUTTONDBLCLK = &H203
            LBUTTONDOWN = &H201
            LBUTTONUP = &H202
            MBUTTONDBLCLK = &H209
            MBUTTONDOWN = &H207
            MBUTTONUP = &H208
            MDIACTIVATE = &H222
            MDICASCADE = &H227
            MDICREATE = &H220
            MDIDESTROY = &H221
            MDIGETACTIVE = &H229
            MDIICONARRANGE = &H228
            MDIMAXIMIZE = &H225
            MDINEXT = &H224
            MDIREFRESHMENU = &H234
            MDIRESTORE = &H223
            MDISETMENU = &H230
            MDITILE = &H226
            MEASUREITEM = &H2C
            MENUCHAR = &H120
            MENUSELECT = &H11F
            MOUSEACTIVATE = &H21
            MOUSEFIRST = &H200
            MOUSELAST = &H209
            MOUSEMOVE = &H200
            MOVE = &H3
            NCACTIVATE = &H86
            NCCALCSIZE = &H83
            NCCREATE = &H81
            NCDESTROY = &H82
            NCHITTEST = &H84
            NCLBUTTONDBLCLK = &HA3
            NCLBUTTONDOWN = &HA1
            NCLBUTTONUP = &HA2
            NCMBUTTONDBLCLK = &HA9
            NCMBUTTONDOWN = &HA7
            NCMBUTTONUP = &HA8
            NCMOUSEMOVE = &HA0
            NCPAINT = &H85
            NCRBUTTONDBLCLK = &HA6
            NCRBUTTONDOWN = &HA4
            NCRBUTTONUP = &HA5
            NEXTDLGCTL = &H28
            NULL = &H0
            PAINT = &HF
            PAINTCLIPBOARD = &H309
            PAINTICON = &H26
            PALETTECHANGED = &H311
            PALETTEISCHANGING = &H310
            PARENTNOTIFY = &H210
            PASTE = &H302
            PENWINFIRST = &H380
            PENWINLAST = &H38F
            POWER = &H48
            Print = &H317
            PSD_ENVSTAMPRECT = (USER + 5)
            PSD_FULLPAGERECT = (USER + 1)
            PSD_GREEKTEXTRECT = (USER + 4)
            PSD_MARGINRECT = (USER + 3)
            PSD_MINMARGINRECT = (USER + 2)
            PSD_PAGESETUPDLG = (USER)
            PSD_YAFULLPAGERECT = (USER + 6)
            QUERYDRAGICON = &H37
            QUERYENDSESSION = &H11
            QUERYNEWPALETTE = &H30F
            QUERYOPEN = &H13
            QUEUESYNC = &H23
            QUIT = &H12
            RBUTTONDBLCLK = &H206
            RBUTTONDOWN = &H204
            RBUTTONUP = &H205
            RENDERALLFORMATS = &H306
            RENDERFORMAT = &H305
            SETCURSOR = &H20
            SETFOCUS = &H7
            SETFONT = &H30
            SETHOTKEY = &H32
            SETREDRAW = &HB
            SETTEXT = &HC
            Size = &H5
            SIZECLIPBOARD = &H30B
            SPOOLERSTATUS = &H2A
            SYSCHAR = &H106
            SYSCOLORCHANGE = &H15
            SYSCOMMAND = &H112
            SYSDEADCHAR = &H107
            SYSKEYDOWN = &H104
            SYSKEYUP = &H105
            SHOWWINDOW = &H18
            Timer = &H113
            TIMECHANGE = &H1E
            UNDO = &H304
            VKEYTOITEM = &H2E
            VSCROLL = &H115
            VSCROLLCLIPBOARD = &H30A
            WINDOWPOSCHANGED = &H47
            WINDOWPOSCHANGING = &H46
            WININICHANGE = &H1A
        End Enum 'Window Messages
 
        Public Shared Function GETTEXTLENGTH(ByVal hwnd As IntPtr) As Integer
            Return DefWindowProc(hwnd, 14, 0, 0) + 1
        End Function
        Public Shared Property TEXT(ByVal hwnd As IntPtr) As String
            Get
                Dim length As Integer = GETTEXTLENGTH(hwnd)
                Dim Handle As IntPtr = Runtime.InteropServices.Marshal.AllocHGlobal(length)
                DefWindowProc(hwnd, 13, length, Handle)
                Return Runtime.InteropServices.Marshal.PtrToStringAnsi(Handle)
            End Get
            Set(ByVal value As String)
                DefWindowProc(hwnd, &HC, IntPtr.Zero, Runtime.InteropServices.Marshal.StringToHGlobalAnsi(value))
            End Set
        End Property
        Public Shared Property FONT(ByVal hwnd As IntPtr) As System.Drawing.Font
            Get
                Return System.Drawing.Font.FromHfont(SendMessage(hwnd, msg.GETFONT))
            End Get
            Set(ByVal value As System.Drawing.Font)
                SendMessage(hwnd, msg.SETFONT, value.ToHfont, True)
            End Set
        End Property
        Public Shared Function CLOSE(ByVal hwnd As IntPtr) As Integer
            Return DefWindowProc(hwnd, msg.CLOSE, 0, 0)
        End Function
        Public Shared Function DESTROY(ByVal hwnd As IntPtr) As Integer
            Return DefWindowProc(hwnd, msg.DESTROY, 0, 0)
        End Function
        Public Shared Function CLEAR(ByVal hwnd As IntPtr) As Integer
            Return DefWindowProc(hwnd, msg.CLEAR, 0, 0)
        End Function
        Public Shared Function UNDO(ByVal hwnd As IntPtr) As Integer
            Return DefWindowProc(hwnd, msg.UNDO, 0, 0)
        End Function
 
        Public Shared Function SYSCOMMAND(ByVal hwnd As IntPtr, ByVal command As SC, Optional ByVal lparam As Integer = 0) As Boolean
            Return DefWindowProc(hwnd, WM.msg.SYSCOMMAND, command, lparam)
        End Function
        Public Shared Function SYSCOMMAND(ByVal hwnd As IntPtr, ByVal command As SC, ByVal x As Short, ByVal y As Short) As Boolean
            Return DefWindowProc(hwnd, WM.msg.SYSCOMMAND, command, New DWORD(x, y).Integer1)
        End Function
    End Class

Don't mind the DefWindowProc, I named it like that by mistake in the beginning :D
If you really want everything in your class, make subclasses with a "msg" enum inside.

Cool, Thanks :) I'll Post My SendMessage Implimentation When i'm Done.

I tried And It seems like I could not create a Generic Implementation of SendMessage. It looks like I will have to Import It each time I need to use it. I got an error .

Quote:

---

PInvoke restriction: cannot return variants.

---

How do you mean a "generic implementation"? Not sure what you are trying to do...
You need SendMessage declared shared, since it is an API. It is independent of your own program.

Every API MUST return a certain type. You can not return an Object, since it can not convert the result to it.
It is like converting a stone to a box of stones.

Note that SendMessage always returns a Boolean or Integer indicating if the API succeeded, so no need to return other types.
For the arguments related: both Lparam and Wparam are always integer or pointer values. In case you have to pass a StringBuilder, you actually pass a pointer to this String in memory.
You could allocate a String in memory instead and send the pointer to that string to SendMessage.

You could also use multiple implementations of SendMessage (like I did):

Code:

---

    Public Shared Function SendMessage(ByVal hWnd As IntPtr, ByVal Msg As UInteger) As Boolean
        Return SendMessage(hWnd, Msg, 0, 0)
    End Function
    Public Shared Function SendMessage(ByVal hWnd As IntPtr, ByVal Msg As UInteger, ByVal wParam As IntPtr) As Boolean
        Return SendMessage(hWnd, Msg, wParam, 0)
    End Function
    Public Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hWnd As IntPtr, ByVal Msg As UInteger, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As Boolean
    Public Declare Function SendMessageO Lib "user32" Alias "SendMessageA" (ByVal hWnd As IntPtr, ByVal Msg As UInteger, Optional ByVal wParam As Object = Nothing, Optional ByVal lParam As Object = Nothing) As Boolean

---

Quote:

---

Originally Posted by BlindSniper

What is the difference between Intptr and a normal Integer ? it seems like they both just contain numeric data ?

---

I should also have mentioned that an Integer is 32-bit on all systems while an IntPtr is 32-bit on 32-bit systems and 64-bit on 64-bit systems.

Strange, I'll keep that in Mind :)

Quote:

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Originally Posted by BlindSniper

Strange, I'll keep that in Mind :)

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Not really. An IntPtr is supposed to store a pointer, i.e. a memory address. Obviously memory addresses are 32-bits wide on 32-bit systems and 64-bits wide on 64-bit systems.