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A call to PInvoke function 'Testing-Class!Testing_Class.Form1::GetClassName' has unbalanced the stack. This is likely because the managed PInvoke signature does not match the unmanaged target signature. Check that the calling convention and parameters of the PInvoke signature match the target unmanaged signature.

What I have tried:

I have add this

[DllImport("User32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        static extern long GetClassName(IntPtr hwnd, StringBuilder lpClassName, long nMaxCount);

[DllImport("User32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        static extern long GetWindowText(IntPtr hwnd, StringBuilder lpString, long cch);

string GetCaptionOfWindow(IntPtr hwnd)
        {
            string caption = "";
            StringBuilder windowText = null;
            try
            {
                int max_length = GetWindowTextLength(hwnd);
                windowText = new StringBuilder("", max_length + 5);
                GetWindowText(hwnd, windowText, max_length + 2); // Its is giving error here

                if (!String.IsNullOrEmpty(windowText.ToString()) && !String.IsNullOrWhiteSpace(windowText.ToString()))
                    caption = windowText.ToString();
            }
            catch (Exception ex)
            {
                caption = ex.Message;
            }
            finally
            {
                windowText = null;
            }
            return caption;
        }

        string GetClassNameOfWindow(IntPtr hwnd)
        {
            string className = "";
            StringBuilder classText = null;
            try
            {
                int cls_max_length = 1000;
                classText = new StringBuilder("", cls_max_length + 5);
                GetClassName(hwnd, classText, cls_max_length + 2);// Its is giving error here

                if (!String.IsNullOrEmpty(classText.ToString()) && !String.IsNullOrWhiteSpace(classText.ToString()))
                    className = classText.ToString();
            }
            catch (Exception ex)
            {
                className = ex.Message;
            }
            finally
            {
                classText = null;
            }
            return className;
        }

Posted 21-May-18 1:29am

Member 11776570

Updated 21-May-18 1:50am

v3

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Alan N · Accepted Answer · 2018-05-21T01:51:00

A working example is

C#

public static String GetText(IntPtr hWnd) {
  // Allocate correct StringBuilder capacity 
  Int32 length = GetWindowTextLength(hWnd);
  StringBuilder sb = new StringBuilder(length + 1);
  GetWindowText(hWnd, sb, sb.Capacity);
  return sb.ToString();
}

The StringBuilder capacity is set for the text length+1 to allow for a null terminator and very importantly the GetWindowText method is given the correct size. Do not add your own padding! The interop marshaller is being clever and treating the StringBuilder as an array of characters and sb.Capacity is the length of that array.

Alan.