Sending Message

Posted on 1998-12-26
Last Modified: 2010-04-04
how do i passing a additional parameter to my message handler ? let say i write my own message and send my additional parameter to my message handler instead of using the LParam and WParam.
Question by:qwertyuiopasdfghjkl
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Expert Comment

ID: 1353156
If your additional data is a record then you use a pointer and send it with the lparam or wparam..

SendMessage(Handle, Message, lparam, longint(@data));
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Expert Comment

ID: 1353157
oh, I forgot, then when you receive it you typecast it like this...

  myrec : TMYREC;
  myRec := TMYREC(msg.lparam^);
 //Then use your record here... It can work for any variable or type or whatever..You just send a pointer with the message...

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Expert Comment

ID: 1353158
is this what you needed??
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Expert Comment

ID: 1353159
Vik's method is a good idea...however, don't you have to pass the pointer thru the LParam?  [If I remember correctly, WParam is a word, and a pointer is a double-word]
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Expert Comment

ID: 1353160
Oppps... Scrappy :) is right... Actualy that's exactly what I've done, but I have a typo that makes it look if I've exchanged the parameters...

This line

SendMessage(Handle, Message, lparam, longint(@data));

should be

SendMessage(Handle, Message, wparam, longint(@data));

sorry for da typo... :))

Does it help now? Am I allowed to answer the q'n?
LVL 12

Expert Comment

ID: 1353161
Scrappy is only half right (sorry to be picky). Yes you should use LParam, but, Wparam in Win32 is a DWORD!



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Expert Comment

ID: 1353162
Yes, Raymond is right. In win16, wParam is 16 bit long, in win32 it is 32 bit long.

However, if you send messages from one application to another, you can't just give in a pointer to a data block, since the pointer will definitely be invalid in the other application's memory context.
So if you're sending this message from one of your applications to another one of your applications, you'll have to look at the WM_COPYDATA message, which is thought for this purpose.
Otherwise (that means if the message is sent and received from the same application) Viktor's solution is right.

Author Comment

ID: 1353163
ok..Viktor can post it as answer now...
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Accepted Solution

viktornet earned 30 total points
ID: 1353164

btw- Madshi is right about the WM_COPYDATA.

Happy New Year (Well almost)


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