C# Signature:

[DllImport("user32.dll",SetLastError = true)]
static extern bool GetWindowInfo(IntPtr hwnd, ref WINDOWINFO pwi);

VB Signature:

Public Declare Auto Function GetWindowInfo Lib "user32" _
(ByVal hwnd As IntPtr, ByRef pwi As WINDOWINFO) As Boolean

VB.Net Signature:

<DllImport("User32.dll",SetLastError = True)> _
Public Function GetWindowInfo(ByVal hwnd As IntPtr, ByRef pwi As WINDOWINFO) As Boolean
End Function

User-Defined Types:

None.

Notes:

You must assign the cbSize parameter prior to calling GetWindowInfo(). For example:

In C#

    WINDOWINFO info = new WINDOWINFO();
    info.cbSize = (uint)Marshal.SizeOf(info);
    GetWindowInfo(Handle, ref info);

In VB

    Dim instance As Process
    Dim info As New WINDOWINFO
    info.cbSize = Convert.ToUInt32(Marshal.SizeOf(info))

To get a WINDOWINFO see http://pinvoke.net/default.aspx/Structures.WINDOWINFO

* WARNING * The size of this (http://pinvoke.net/default.aspx/Structures.WINDOWINFO) structure is 96 bytes, while what the function expects is 60 bytes. The structure format is wrong.

The correct structure format is as follows:

    [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
    public struct tagWINDOWINFO
    {
        /// DWORD->unsigned int
        public uint cbSize;

        /// RECT->tagRECT
        public tagRECT rcWindow;

        /// RECT->tagRECT
        public tagRECT rcClient;

        /// DWORD->unsigned int
        public uint dwStyle;

        /// DWORD->unsigned int
        public uint dwExStyle;

        /// DWORD->unsigned int
        public uint dwWindowStatus;

        /// UINT->unsigned int
        public uint cxWindowBorders;

        /// UINT->unsigned int
        public uint cyWindowBorders;

        /// ATOM->WORD->unsigned short
        public ushort atomWindowType;

        /// WORD->unsigned short
        public ushort wCreatorVersion;
    }

with tagRECT being:

    [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
    public struct tagRECT
    {

        /// LONG->int
        public int left;

        /// LONG->int
        public int top;

        /// LONG->int
        public int right;

        /// LONG->int
        public int bottom;
    }

* UPDATE * The proposed "fixed" structure above is the same. The difference is in the fact that the default packing size in managed code is 8 bytes, while the default packing in unmanaged code is 4 bytes. So, when marshalled to the API, the struct size is 60.

By the way, the StructLayoutAttribute is optional, because the C# compiler applies by default the Sequential layout kind on structures (but not on classes).

Tips & Tricks:

Note that the members of the RECT structure should be int, not long. In some other API functions they are long, so this can be confusing.

Sample Code:

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Alternative Managed API:

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