Question

I’m trying to send the MCM_GETSELRANGE windows message to a standard MonthCalendar. Based on the documentation I have tried the following with no luck (the dates come back as nothing [as in they are not set to anything other than zero], however I do get a non-zero return value which seems to indicate that it succeeded?):

using System;
using System.Runtime.InteropServices;

namespace GetSelRange
{
    class Program
    {
        static void Main(string[] args)
        {
            IntPtr targetWindowHandle = new IntPtr(68684130);
            SYSTEMTIME[] dateRange = new SYSTEMTIME[2];
            IntPtr success = SendMessage(targetWindowHandle, MCM_GETSELRANGE, IntPtr.Zero, dateRange);
        }

        #region Win32API

        const uint MCM_FIRST = 0x1000;
        const uint MCM_GETSELRANGE = MCM_FIRST + 5;

        [StructLayout(LayoutKind.Sequential)]
        private struct SYSTEMTIME
        {
            [MarshalAs(UnmanagedType.U2)]
            public ushort Year;
            [MarshalAs(UnmanagedType.U2)]
            public ushort Month;
            [MarshalAs(UnmanagedType.U2)]
            public ushort DayOfWeek;
            [MarshalAs(UnmanagedType.U2)]
            public ushort Day;
            [MarshalAs(UnmanagedType.U2)]
            public ushort Hour;
            [MarshalAs(UnmanagedType.U2)]
            public ushort Minute;
            [MarshalAs(UnmanagedType.U2)]
            public ushort Second;
            [MarshalAs(UnmanagedType.U2)]
            public ushort Milliseconds;
        }

        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, SYSTEMTIME[] lParam);

        #endregion
    }
}

pinvoke.net does not seem to have any suggestions as to how this should be called.

Thank you

Answer 1

Clearly you are sending this to a window that belongs to another process. That cannot work like this, the SYSTEMTIME array is only valid in your process, not the other one. This considerably complicates the code, you have to allocate memory in the target process.

I’ll briefly describe the pinvoke required, you should have no trouble googling sample code from the api function names. First you need GetWindowThreadProcessId() to get the ID of the process that owns the window. OpenProcess() to open a handle to it. VirtualAllocEx() to allocate the memory.

SendMessage() to send the message as you did before, passing the pointer you got from VirtualAllocEx(). ReadProcessMemory() to read the array content out of the process. Clean up with VirtualFreeEx() and CloseHandle(). It is not unlikely you will be battling security problems btw, these are privileged functions.