Problem with SendMessage

Question

I am developing an application using C# having similar functionality of copy,paste as in Windows. I have added menu items and linked with respective applications.

Please look at the following image for getting more idea.

Items added to shell menu http://softwaregenius.net/myimages/menu.jpg

Like we select multiple items in windows explorer, you need to select multiple files and/or folders and then select OS Util->FastCopy. A form is opened as shown below

Form shown on FastCopy http://softwaregenius.net/myimages/fastcopy1.jpg

The application is working perfectly. The major problem here is that after selecting the files all these files are opening up within there respective softwares. That is if i selected word document then the filename is added to FastCopy form but the is also opening up within Word also.

When i investigate i found that this problem is due to SendMessage. I have to use PostMessage instead of SendMessage. But when i do so the application is not working.

Below is my Main function coding in C# 2005

static class Program
{
    static Mutex mutex = new Mutex(true, "{8F6F0AC4-B9A1-45fd-A8CF-72F04E6BDE92}");
    [STAThread]
    static void Main(string[] args)
    {
        string fileName = "";
        if (args.Length > 0)
        {
            fileName = args[0];
        }
        if (mutex.WaitOne(TimeSpan.Zero, true))
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            frmFastCopy frm = new frmFastCopy();
            frm.AddItemToList(fileName);
            Application.Run(frm);

        }
        else
        {
            //The following message is sent just to show up the form
            NativeMethods.PostMessage(
                    (IntPtr)NativeMethods.HWND_BROADCAST,
                    NativeMethods.WM_SHOWME,
                    IntPtr.Zero,
                    IntPtr.Zero);

            //Send the filename
            SendFileName(fileName);
        }
    }

    static void SendFileName(string s)
    {
        Win32.CopyDataStruct cds = new Win32.CopyDataStruct();

        cds.cbData = (s.Length + 1) * 2;
        cds.lpData = Win32.LocalAlloc(0x40, cds.cbData);
        Marshal.Copy(s.ToCharArray(), 0, cds.lpData, s.Length);
        cds.dwData = (IntPtr)1;
        Win32.SendMessage((IntPtr)NativeMethods.HWND_BROADCAST, Win32.WM_COPYDATA, IntPtr.Zero, ref cds);
        //NativeMethods.PostMessage((IntPtr)NativeMethods.HWND_BROADCAST, Win32.WM_COPYDATA, cds.lpData, IntPtr.Zero);
    }
}

}

---

Below is the copy for WndProc and other code from within the Form

public partial class frmFastCopy : Form { delegate void AddItemToListDelegate(string itm);

    public frmFastCopy()
    {
        InitializeComponent();
    }

    public void AddItemToList(string itm)
    {
        if (lvFilesAndFolders.InvokeRequired)
        {
            AddItemToListDelegate m = new AddItemToListDelegate(AddItemToList);
            this.Invoke(m, new object[] { itm });
        }
        else
        {
            lvFilesAndFolders.Items.Add(itm);
        }
    }
    protected override void WndProc(ref Message m)
    {
        if (m.Msg==NativeMethods.WM_SHOWME)
        {
                ShowMe();
        }
        if (m.Msg==Win32.WM_COPYDATA)
        {
                //string s = Marshal.PtrToStringUni(m.LParam);
                MessageBox.Show("Got message");

                Win32.CopyDataStruct st = (Win32.CopyDataStruct)Marshal.PtrToStructure(m.LParam, typeof(Win32.CopyDataStruct));
                string strData = Marshal.PtrToStringUni(st.lpData);
                AddItemToList(strData);
        }
        base.WndProc(ref m);
    }
    private void ShowMe()
    {
        this.Show();
        if (WindowState == FormWindowState.Minimized)
        {
            WindowState = FormWindowState.Normal;
        }
        // get our current "TopMost" value (ours will always be false though)
        bool top = TopMost;
        // make our form jump to the top of everything
        TopMost = true;
        // set it back to whatever it was
        TopMost = top;
    }

---

Here is the NativeCode class

internal class NativeMethods
{
    public const int HWND_BROADCAST = 0xffff;
    public static readonly int WM_SHOWME = RegisterWindowMessage("WM_SHOWME");
    [DllImport("user32")]
    public static extern bool PostMessage(IntPtr hwnd, int msg, IntPtr wparam, IntPtr lparam);
    [DllImport("user32")]
    public static extern int RegisterWindowMessage(string message);

}

I know you guys are genius. Could someone tell me where should i make changes to that the selected files should be opened or rather how i should use postmessage.

Thanks for sharing your valuable time.

Regards

Irfan

Answer 1

Please look at my comment (I wonder why you don't use the Clipboard class here). But ignoring that: Why do you broadcast the message?

Can you locate your application (by name, window class, whatever) and only send the message to your own application ?

---

To elaborate on the message handling: You say regarding HWND_BROADCAST in the comments below:

Thats nothing but the global handle to my application.

No, it's not. It is a special value that tells Windows "this message is for all applications". You are sending a WM_SHOWME to all applications. Which is why I asked why you would want to do that?

Please see this post on the old new things blog regarding message broadcasts.