Right, I've got a 2 c# programs here. Lets call them A and B. My aim is to send a simple string from B to A.
A is always running. I've overridden the WndProc method to give me messages that are sent to it. B is a program that loads, sends a message and then quits. Let me give you the code to B (bits are missed out, but I've got the important stuff there):
So there we go. I send a reference to a stringbuilder that contains the string that I want to send "hi there".
Here's the relevant bit of A's WndProc:
Now, when I run A in debug mode and run B, I can always catch the code getting to this case. I step it through, and it throws an exception at the PtrToStructure line:
Ok, so some reading about tells me that a stringbuilder is not a blittable structure. So lets try with an int. I send a ref int and try to read it as an int (using typeof(int) and everything). This time, the int I read out is the same as the int value of lParam. So it's reading itself as an int and not the int object I put in in program B (42, btw). Ok, so lets send an int and not a ref int.
WTF? What the hell is null here? certainly not lParam, that's 1274539 or something. Why can't I send even a simple int from one .NET program to another?
Anyone got any ideas?
P.S. I had one idea but not been able to test this one out - is there a danger that B is sending a pointer to the memory for A to get hold of, but then quitting before A can do anything with it and therefore de-allocating it's memory making the pointer not valid?
A is always running. I've overridden the WndProc method to give me messages that are sent to it. B is a program that loads, sends a message and then quits. Let me give you the code to B (bits are missed out, but I've got the important stuff there):
Code:
private const uint WM_USER_SENDTEXT = 0x8001;
[DllImport("user32.dll", CharSet = CharSet.Auto)]
static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, ref StringBuilder lParam);
public arghandler(string assemblyname,string[] args)
{
IntPtr hWnd = FindWindow(null, "ProgramA");
if (hWnd!=IntPtr.Zero)
{
StringBuilder sb = new StringBuilder("hi there");
IntPtr res = SendMessage(hWnd,WM_USER_SENDTEXT,IntPtr.Zero,ref sb);
bool rah = SetForegroundWindow(hWnd);
}
this.Close();
}Here's the relevant bit of A's WndProc:
Code:
case WM_USER_SENDTEXT:
StringBuilder sb = new StringBuilder();
try
{
sb = (StringBuilder)Marshal.PtrToStructure(m.LParam,typeof(StringBuilder));
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
MessageBox.Show("Hey! Got a message here "+sb.ToString());
break;Now, when I run A in debug mode and run B, I can always catch the code getting to this case. I step it through, and it throws an exception at the PtrToStructure line:
Code:
_message "The specified structure must be blittable or have layout information." stringOk, so some reading about tells me that a stringbuilder is not a blittable structure. So lets try with an int. I send a ref int and try to read it as an int (using typeof(int) and everything). This time, the int I read out is the same as the int value of lParam. So it's reading itself as an int and not the int object I put in in program B (42, btw). Ok, so lets send an int and not a ref int.
Code:
_message "Object reference not set to an instance of an object." stringAnyone got any ideas?
P.S. I had one idea but not been able to test this one out - is there a danger that B is sending a pointer to the memory for A to get hold of, but then quitting before A can do anything with it and therefore de-allocating it's memory making the pointer not valid?