Marshaling Struct for native SendMessage

[michelqa]

Hi,

I need to call a lot of different native SendMessage to retreive
informations from non managed application.

Some win32 messages use struct pointer for lparam....how to create and
marshaling the struct to be able to use it in sendmessage...

Here is an example LM_GETITEM:
http://msdn.microsoft.com/en-us/libr...20(VS.85).aspx
---------------------------------------------------------

[DllImport("user 32.dll")]
public static extern IntPtr SendMessage(Int Ptr hwnd, int msg, IntPtr
wparam, IntPtr lparam);
//...
[StructLayout(La youtKind.Sequen tial)]
public struct LITEM
{
uint mask;
int iLink;
uint state;
uint stateMask;
[MarshalAs(Unman agedType.ByValT Str, SizeConst = 260)]
string szID; //??? is it equivalent to WCHAR ?//
[MarshalAs(Unman agedType.ByValT Str, SizeConst = 260)]
string szUrl; //??? is it equivalent to WCHAR ?//
}

LITEM MyLItem = new LITEM();
int MsgResult = SendMessage(Han dle,LM_GETITEM, IntPtr.Zero,ref
MyLItem); //<----- ???????

I know the information in the struct must be set before calling
sendmessage...t he code is just an incomplete example, but how to
create and marshaling a valid struct to call sendmessage in this
case? Is it possible when the Handle is in a different process??

Thanks for any help and example...

[Pavel Minaev]

Re: Marshaling Struct for native SendMessage

On Jul 13, 1:10 pm, michelqa <miche...@yahoo .cawrote:

Hi,
>
   I need to call a lot of different native SendMessage to retreive
informations from non managed application.
>
Some win32 messages use struct pointer for lparam....how to create and
marshaling the struct to be able to use it in sendmessage...
>
Here is an example LM_GETITEM:http://msdn.microsoft.com/en-us/libr...20(VS.85).aspx
---------------------------------------------------------
>
[DllImport("user 32.dll")]
public static extern IntPtr SendMessage(Int Ptr hwnd, int msg, IntPtr
wparam, IntPtr lparam);
//...
[StructLayout(La youtKind.Sequen tial)]
public struct LITEM
{
        uint mask;
        int iLink;
        uint state;
        uint stateMask;
        [MarshalAs(Unman agedType.ByValT Str, SizeConst = 260)]
        string szID;    //??? is it equivalent to WCHAR  ?//
        [MarshalAs(Unman agedType.ByValT Str, SizeConst = 260)]
        string szUrl;   //??? is it equivalent to WCHAR  ?//
>
}
>
LITEM MyLItem = new LITEM();
int MsgResult = SendMessage(Han dle,LM_GETITEM, IntPtr.Zero,ref
MyLItem);   //<----- ???????
>
I know the information in the struct must be set before calling
sendmessage...t he code is just an incomplete example, but how to
create and marshaling a valid struct to call sendmessage in this
case?

Consider using Marshal.Structu reToPtr() method. You'll need to
allocate a memory block of proper size first, then call StructureToPtr
to marshal your structure into that block in the appropriate format,
and then you can pass the address of that block as IntPtr to
SendMessage.

Is it possible when the Handle is in a different process??

It is, though it has no relevance to P/Invoke marshalling - it's the
SendMessage function itself that checks whether a handle belongs to a
different process, and does any further necessary marshalling to
deliver it properly. However, this SendMessage feature only works for
Win32 predefined message types (with codes less than WM_USER), not for
any custom messages.

[michelqa]

Re: Marshaling Struct for native SendMessage

Thanks for your help... I really need help on this :(

Ok now my code look like this... but sendMessage return 0
- Is anybody can confirm that the code look correct (for passing a
structure pointer to sendmessage??)
- After calling sendmessage how can I access to the structure
information returned by MyLItemPtr???
- Since LM_GETITEM is WM_USER +771.... I suspect I need other
marshaling to get the structure back with the information??

//----------- BEGIN CODE -------------//
[DllImport("user 32.dll")]
public static extern IntPtr SendMessage(Int Ptr hwnd, int msg, IntPtr
wparam, IntPtr lparam);
//...
int WM_USER =1024,
int LM_GETITEM = (WM_USER + 0x303)
int LIF_ITEMINDEX = 1;
int LIF_URL = 8;

//..
[StructLayout(La youtKind.Sequen tial)]
public struct LITEM
{
uint mask;
int iLink;
uint state;
uint stateMask;
[MarshalAs(Unman agedType.ByValT Str, SizeConst = 48)]
string szID; //??? is it equivalent to WCHAR ?//
[MarshalAs(Unman agedType.ByValT Str, SizeConst = 2084)]
string szUrl; //??? is it equivalent to WCHAR ?//
}


LITEM MyLItem = new LITEM();
MyLItem.mask=(u int)LIF_ITEMID | (uint)LIF_URL; //must use these
masks to get the url
MyLItem.iLink=0 ;
IntPtr MyLItemPtr = Marshal.AllocHG lobal(Marshal.S izeOf(MyLItem)) ;
Marshal.Structu reToPtr(MyLItem , MyLItemPtr, false);
IntPtr MsgResult =
Win32.SendMessa ge(Handle,LM_GE TITEM,IntPtr.Ze ro,MyLItemPtr);
MessageBox.Show (MsgResult.ToSt ring()); //this return 0 :(
Marshal.FreeHGl obal(MyLItemPtr );
//----------- END CODE -------------//

Thanks again

[michelqa]

Re: Marshaling Struct for native SendMessage

Still playing with the code all day without any success :(

I desperately need help

[Peter Duniho]

Re: Marshaling Struct for native SendMessage

On Sun, 13 Jul 2008 22:32:31 -0700, michelqa <michelqa@yahoo .cawrote:

Still playing with the code all day without any success :(
>
I desperately need help

For what it's worth, there is a newsgroup specifically dedicated to
interop questions like yours:
microsoft.publi c.dotnet.framew ork.interop

You may have better luck getting your question answered there, especially
if you're in a rush.

Pete

[michelqa]

Re: Marshaling Struct for native SendMessage

Thanks for the suggestion.. I post my problem in this newsgroup also.

For now I will maybe try to recreate this directly in a win32 project
to make sure the problem is not a misunderstandin g of the LM_GETITEM
API....but by looking at the LM_GETITEM in controlSpy my parameters
seems to be ok. (http://www.microsoft.com/downloads/details.aspx?
familyid=19d429 4d-0531-4ec2-8b27-2e463b315f16&di splaylang=en)