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Editorial Team
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Asked: 2026-05-20T14:13:21+00:00

According to my research, when I run C# executable which opens WinForm, within .NET,

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According to my research, when I run C# executable which opens WinForm, within .NET, they don’t offer the function to access those WinForm object from separate c# process (separate file I mean) but win32 API does.

Then I came across 3 functions from API.

FindWindow();
GetWindowLong();
CallWindowProc()

I need to call it from top down to the bottom but then I got stuck by CallWIndowProc() because
I can’t figure what I should pass for last 3 arguments.

private static extern UIntPtr CallWindowProc(IntPtr a, IntPtr b, uint c, IntPtr d, IntPtr e);

c, d and e

According to the doc, it should be some sort of “message” which is int. But where can I get such value???

http://msdn.microsoft.com/en-us/library/ms633571(v=vs.85).aspx

Code:

 [DllImportAttribute("User32.dll")]
 private static extern IntPtr FindWindow(String ClassName, String WindowName);
 [DllImportAttribute("User32.dll")]
 private static extern long GetWindowLong(IntPtr a, int b);
 [DllImportAttribute("User32.dll")]
 private static extern UIntPtr CallWindowProc(IntPtr a, IntPtr b, uint c, IntPtr d, IntPtr e);

 [STAThread]
 static void Main(string[] args)
 {
    IntPtr lResult;
    uint lMsg = 0;
    IntPtr HWND = FindWindow("WindowsFormsApplication1.Form1", "Form1");
    int GWL_WNDPROC = -4;
    long WNDPROC = GetWindowLong(HWND, GWL_WNDPROC);
    lResult = CallWindowProc(WNDPROC, HWND, lMsg, 0, 0);
 }

Clarification

OK.. I should have made it clear.. my goal is to run following chunk of code against the WebForm being executed. (I’ts WatiN)

var t = new Thread(() =>
{
  Settings.AutoStartDialogWatcher = false;
  var ie = new IE(form1.webBrowser1.ActiveXInstance);
  ie.GoTo("http://www.google.com");
  ie.TextField(Find.ByClass("lst")).TypeText("this is awesome!!");
  ie.Button(Find.ByName("btnG")).Click();
});
t.SetApartmentState(ApartmentState.STA);
t.Start();
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1 Answer

  1. Editorial Team

    What message you are trying to send to callWinProc?

    Arguments are

    nProc is a value returned previously by SubClassWindow() (Source Window).

    hWnd is the handle to the window that was subclassed (target window).

    nMsg is the message (one of the WM_* values defined in WINDOWS.CH, basically kind of event or message like click is one message). For complete system messages see http://msdn.microsoft.com/en-us/library/ms644927(v=vs.85).aspx#system_defined

    wParam depends on nMsg. For click, it takes left or right click

    lParam depends on nMsg. for click it takes the location as lparam

    you can see wparam and lparam defination for each message.

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