How to send object instances to WndProc

Question

I'm using my custom class that describes some states and values:

  class MyClass
    {
        int State;
        String Message;
        IList<string> Values;
    }

Because of application architecture, for forms interaction is used messages and its infrastructure (SendMessage/PostMessage, WndProc). The question is - how, using SendMessage/PostMessage, to send an instance of MyClass to WndProc? In my code PostMessage is defined next way:

[DllImport("user32.dll", SetLastError = true)]
public static extern bool PostMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);

So, I need that below my custom message number somehow to send and an MyClass instance, so in WndProc I could use it for logics needs. It's possible?

Don't; it's a bad idea. Why do you need to do this? – SLaks Jun 28 '11 at 15:09 — SLaks, Jun 28 '11 at 15:09

score 2 · Accepted Answer · edited May 23 '17 at 12:04

You won't be able to do that. Pointers in a managed language mean nothing, they are often relocated and killed when no longer referenced. Well maybe you would be able to achieve something that kinda works this way (in process), with unsafe code and pinned pointers but that will be your doom.

If you want only inprocess communication then beware of cross thread communication implications.

If you need cross process communication see this thread: IPC Mechanisms in C# - Usage and Best Practices

Edit:

Sending uniqueID through SendMessage to fetch serialized object. I don't advise to to this since it is hacking and bug prone but you requested:

when sending the message:

IFormatter formatter = new BinaryFormatter();
string filename = GetUniqueFilenameNumberInFolder(@"c:\storage"); // seek a freee filename number -> if 123.dump is free return 123 > delete those when not needed anymore
using (FileStream stream = new FileStream(@"c:\storage\" + filename + ".dump", FileMode.Create))
{
   formatter.Serialize(stream, myClass);
}
PostMessage(_window, MSG_SENDING_OBJECT, IntPtr.Zero, new IntPtr(int.Parse(filename)));

when receiving in WndProc:

if (msg == MSG_SENDING_OBJECT)
{
    IFormatter formatter = new BinaryFormatter();
    MyClass myClass;
    using (FileStream stream = new FileStream(@"c:\storage\" + lParam.ToInt32().ToString() + ".dump", FileMode.Open))
    {
        myClass = (MyClass)formatter.Deserialize(stream);
    }
    File.Delete(@"c:\storage\" + lParam.ToInt32().ToString() + ".dump");
}

Sorry for typos in the code, I'm writing this ad hoc and cannot test...

The application have to be runned more that once instance, but it should only one instance remain - every new instance "add" some new data. To accomplish the single-instance logics is used Mutex class - if the logics detects that an instance is already running - it will send an message using SendMessage/PostMessage, where additionally should be send and the new data - in my case that data is wrapped in a class instance. The question - how to send that class instance to be processed in form's WndProc? Or could You propose another way. — DreadAngel, Jun 28 '11 at 15:42
If I understood correctly, I cant help you with this. It seems awful design. This kind of requirement fits a client-server application. That probably is of no use to you since you already have something to extend. — Marino Šimić, Jun 28 '11 at 16:24
Maybe you can serialize that object somewhere and store that cached object with a predetermined index. Then send this index instead of the pointer, fetch the object from the storage with the index you get from the Param, and deserialize it. — Marino Šimić, Jun 28 '11 at 16:28
Ok - I admit that I could serialize - and have an string... Could You provide a piece of code that reflects that? Both SendMessage(..) and Wndroc catch block? — DreadAngel, Jun 28 '11 at 16:39

How to send object instances to WndProc

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