Passing messages from Delphi DLL to application - delphi

Question

I have a delphi application loading a delphi dll which will send messages back to it. For testing, I have the dll sending message to another application, but they are not showing up.
dll code
type
TSampleRecord = packed record
card : string[50];
end;
var
handle: HWND;
procedure PrepareDLL(AppHandle : HWND); stdcall;
begin
handle := AppHandle;
end;
procedure ConfigccDLL(Variables: PChar); stdcall;
var
sampleRecord: TSampleRecord;
copyDataStruct: TCopyDataStruct;
receiverHandle: HWND;
begin
sampleRecord.card := 'FakeCard';
copyDataStruct.dwData := Integer(2);
copyDataStruct.cbData := SizeOf(sampleRecord);
copyDataStruct.lpData := #sampleRecord;
receiverHandle := FindWindow(PChar('TReceiverMainForm'),PChar('ReceiverMainForm'));
SendMessage(receiverHandle, WM_COPYDATA, Integer(Handle), Integer(#copyDataStruct));
end;
Receiver code
type
TSampleRecord = packed record
card : string[50];
end;
TReceiverMainForm = class(TForm)
cdMemo: TMemo;
procedure FormCreate(Sender: TObject);
private
procedure WMCopyData(var Msg : TWMCopyData); message WM_COPYDATA;
procedure HandleCopyDataRecord(copyDataStruct : PCopyDataStruct);
end;
var
ReceiverMainForm: TReceiverMainForm;
implementation
procedure TReceiverMainForm.FormCreate(Sender: TObject);
begin
cdMemo.Clear;
end;
procedure TReceiverMainForm.HandleCopyDataRecord(
copyDataStruct: PCopyDataStruct);
var
CodeRcvd: string;
sampleRecord : TSampleRecord;
begin
sampleRecord.card := TSampleRecord(CopyDataStruct.lpData^).card;
CodeRcvd := '$B';
cdMemo.Lines.Add(Format('Received record at %s',[DateToStr(Now)]));
cdMemo.Lines.Add(CodeRcvd);
cdMemo.Lines.Add(Format('sampleRecord.card = %s',[sampleRecord.card]));
cdMemo.Lines.Add(Format('sampleRecord size: %d %d',[SizeOf(sampleRecord), copyDataStruct.cbData]));
end;
procedure TReceiverMainForm.WMCopyData(var Msg: TWMCopyData);
begin
cdMemo.Lines.Add(Format('WM_CopyData from: %d',[msg.From]));
HandleCopyDataRecord(Msg.CopyDataStruct);
msg.Result := cdMemo.Lines.Count;
end;
end.
PrepareDLL gets passed the handle of the delphi application which calls the DLL.
The last two functions aren't implemented yet. I can post the receiver code if needed but it is working fine with other delphi applications built to be 'sender's.
The functions themselves get called fine, ShowMessage() function calls work.
I've checked the return code of SendMessage and RaiseLastError and they both state success.
I have a feeling this might have to do with UIPI but I've checked the 'integrity' of both applications with ProcessExplorer and they are both set to Medium.
This is on Windows Vista.

Answer 1

It does not work for me on Windows 10 only if Receiver is run as administrator. In this case you'll need following to allow it.
type
TChangeFilterStruct = packed record
cbSize: DWORD;
ExtStatus: DWORD;
end;
PChangeFilterStruct = ^TChangeFilterStruct;
const
MSGFLT_ALLOW = 1;
MSGFLT_DISALLOW = 2;
MSGFLT_RESET = 0;
{$WARN SYMBOL_PLATFORM OFF}
function ChangeWindowMessageFilterEx(Wnd: HWND; Message: UINT; Action: DWORD;
ChangeFilterStruct: PChangeFilterStruct): Bool; stdcall; external 'User32.dll' delayed;
{$WARN SYMBOL_PLATFORM ON}
ChangeWindowMessageFilterEx(ReceiverWindowHandle, WM_COPYDATA, MSGFLT_ALLOW, nil);
Update
Actually this function only exists since Windows 7, for Vista you need to use
ChangeWindowMessageFilter