Messages (C++)

Description

This is an example demonstrating the usage of the SendGetIntMessage, SendStructMessage, SendGetStructMessage, and SendTextMessage message functions. This example uses four buttons and six text edit boxes, as follows:

• Button1 SendGetIntMessage
• Button2 SendStructMessage
• Button3 SendGetStructMessage
• Button4 SendTextMessage

• IntEdit For int inputs
• StructEdit1 & StructEdit2 For struct inputs (ints)
• GetStructEdit1 & GetStructEdit2 For struct inputs (ints)
• TextEdit for text input

Note: This example works correctly when the default STRICT conditional define is set. However, the example generates unresolved external errors with the NO_STRICT conditional define set.

This example uses three custom message structures defined in the header:

struct TMyIntMessage { Cardinal Msg; int* wparam; int* lparam; LRESULT Result; };

struct TMyTextMessage { Cardinal Msg; int wparam; String lparam; LRESULT Result; };

struct MStruct { int m_a; int m_b; };

struct TMyStruct { Cardinal Msg; int wparam; MStruct* lparam; LRESULT Result; };

Furthermore it uses four message handling functions described in the header, along with a message map:

Code

MESSAGE void __fastcall UserIntHandler(TMyIntMessage &msg);
MESSAGE void __fastcall UserStructHandler(TMyStruct &msg);
MESSAGE void __fastcall UserGetStructHandler(TMyStruct &msg);
MESSAGE void __fastcall UserTextHandler(TMyTextMessage &msg);
 
BEGIN_MESSAGE_MAP
        MESSAGE_HANDLER(WM_INTMESSAGE, TMyIntMessage, UserIntHandler);
        MESSAGE_HANDLER(WM_GETSTRUCTMESSAGE, TMyStruct, UserGetStructHandler);
        MESSAGE_HANDLER(WM_STRUCTMESSAGE, TMyStruct, UserStructHandler);
        MESSAGE_HANDLER(WM_TEXTMESSAGE, TMyTextMessage, UserTextHandler);
END_MESSAGE_MAP(TComponent)
 
*/
 
void __fastcall TForm4::UserIntHandler(TMyIntMessage &msg){
        MessageDlg("Int message received: " + IntToStr(*msg.lparam),
                        mtInformation, TMsgDlgButtons() << mbOK, 0);
 
        *msg.lparam = *msg.lparam + 50;
}
void __fastcall TForm4::UserStructHandler(TMyStruct &msg){
        MessageDlg("Struct received: " + IntToStr(msg.lparam->m_a) +
                                " " + IntToStr(msg.lparam->m_b),
                        mtInformation, TMsgDlgButtons() << mbOK, 0);
}
void __fastcall TForm4::UserGetStructHandler(TMyStruct &msg){
        MessageDlg("Struct received: " + IntToStr(msg.lparam->m_a) +
                        "" + IntToStr(msg.lparam->m_b),
                        mtInformation, TMsgDlgButtons() << mbOK, 0);
        msg.lparam->m_a = msg.lparam->m_a + 50;
        msg.lparam->m_b = msg.lparam->m_b + 50;
}
void __fastcall TForm4::UserTextHandler(TMyTextMessage &msg){
        MessageDlg("Text received: " + msg.lparam,
                        mtInformation, TMsgDlgButtons() << mbOK, 0);
}
void __fastcall TForm4::Button1Click(TObject *Sender)
{
        int wparam = 0;
        int lparam = StrToIntDef(IntEdit->Text,0);
        int lbase = lparam;
 
        SendGetIntMessage(Handle,WM_INTMESSAGE,wparam,lparam);
 
        if (lbase != lparam)
        {
                MessageDlg("Value modified by handler function: " +
                                        IntToStr(lparam),
                                        mtInformation, TMsgDlgButtons() << mbOK, 0);
                IntEdit->Text = IntToStr(lparam);
        }
 
}
//---------------------------------------------------------------------------
 
void __fastcall TForm4::Button2Click(TObject *Sender){
        int wparam = 0;
        String lparam = TextEdit->Text;
 
        SendTextMessage(Handle,WM_TEXTMESSAGE,wparam,lparam);
}
//---------------------------------------------------------------------------
 
void __fastcall TForm4::Button3Click(TObject *Sender)
{
        int wparam = 0;
        MStruct lparam;
 
        lparam.m_a = StrToIntDef(StructEdit1->Text,0);
        lparam.m_b = StrToIntDef(StructEdit2->Text,0);
 
        SendStructMessage(Handle, WM_STRUCTMESSAGE, wparam, &lparam);
}
//---------------------------------------------------------------------------
 
void __fastcall TForm4::Button4Click(TObject *Sender)
{
        int wparam = 0;
        MStruct lparam, lbase;
 
        lparam.m_a = StrToIntDef(GetStructEdit1->Text,0);
        lparam.m_b = StrToIntDef(GetStructEdit2->Text,0);
 
        lbase = lparam;
 
        SendStructMessage(Handle, WM_GETSTRUCTMESSAGE, wparam, &lparam);
 
        if (lbase.m_a != lparam.m_a) {
        MessageDlg("Struct modified by handler function: " +
                                        IntToStr(lparam.m_a) + " " + IntToStr(lparam.m_b),
                                        mtInformation, TMsgDlgButtons() << mbOK, 0);
                GetStructEdit1->Text = IntToStr(lparam.m_a);
                GetStructEdit2->Text = IntToStr(lparam.m_b);
        }
}
//---------------------------------------------------------------------------

Uses

• Winapi.Messages.SendGetIntMessage ( fr | de | ja )
• Winapi.Messages.SendStructMessage ( fr | de | ja )
• Winapi.Messages.SendGetStructMessage ( fr | de | ja )
• Winapi.Messages.SendTextMessage ( fr | de | ja )

See Also

• MessageDlg (C++)