AfterScroll Event in a derived class

[hansaplast]

Hi,

I'm trying to write an AfterScroll event for my TDBApp class but dunno
how to implement this.

I want to do someting like this in my App.

// MyApp.cpp
#include DBApp.h
void MyApp::somefunction()
{
TDBApp *pDBApp = new TDBApp(NULL);

// How do I implement this functionality??
pDBApp->AfterScroll = MyOwnAfterScrollFunction;
}

void MyApp::MyOwnAfterScrollFunction(/*With params*/){
// Do something...
}


// DBApp.h
class TDBApp : public TDatabase {
// ...
protected:
TTable *pArchive;
// ...
public:
// Overriding the default constructor
virtual __fastcall TDmsDB(Classes::TComponent* AOwner);
}

// DBApp.cpp
__fastcall TDmsDB::TDmsDB(Classes::TComponent*
AOwner):TDatabase(AOwner)
{
pArchive->AfterScroll = ArchiveAfterScroll;
// TDatabase Specific...
// pArchive->AfterScroll is fired as soon as the application
// scrolls from one record to another.
}

void __fastcall TDmsDB::ArchiveAfterScroll(TDataSet * DataSet)
{
if (pArchive->Active) {
// ...
// *HERE I want to FIRE the "DBApp::AfterScroll" Event
// to whatever function is attached to it
// How to do this???
// ...
}
}

Regards,

Hanza

 

[Supernat03]

As a simple example:

MyClass.h file
class MyClass : TObject
{
private:
TNotifyEvent FOnSomething;
public:
__published:
__property TNotifyEvent OnSomething = {read=FOnSomething, write=FOnSomething};
};

MainForm.h file
class TMainForm : TForm
{
//usual stuff here...
MyClass *Mine;
void __fastcall SomeFunction(void);
void __fastcall HandleOnSomething(TObject *Sender);
}

MainForm.cpp file
void __fastcall MainForm::SomeFunction(void)
{
Mine = new MyClass(SomeParameters);
Mine->OnSomething = HandleOnSomething;
delete Mine;
}

Now, assume you want to pass in parameters other than TObject *Sender.

Let's look at what TNotifyEvent really is. It's a function prototype.

typedef void __fastcall (__closure *TNotifyEvent) (System::TObject* Sender);

So, follow that concept with your own function. Say you want to pass in 2 integers to the event handler.

typedef void __fastcall (__closure *TOnSomethingEvent) (int Int1, int Int2);

Now just replace TNotifyEvent with TOnSomethingEvent in your class definition. Then replace the parameters in your main form's event handler function. That's all there is to it!

Good luck,
Chris

 

[hansaplast]

Thanks Super,

Got the idea.
Next problem is that I don't know how to fire the Event I've just created. How do I execute the function which "FOnSomething" points to?

 

[hansaplast]

Nevermind

The Sollution:
OnSomething(/*TObject*/);

Thankz anyway

 

[hansaplast]

Just to complete things. It could be handy for other programmers
Let me show you what I have:

// MyDB.h
(irrelevant function prototypes are left away)

class TMyDB : public TDatabase {
private:
// typedef void __fastcall (__closure *TDataSetNotifyEvent)(TDataSet* DataSet);
TDataSetNotifyEvent FAfterScroll;

protected:
void __fastcall AppAfterScroll(TDataSet *DataSet);

public:
void __fastcall FireScrollEvent(TDataSet * DataSet);

__published:
__property TDataSetNotifyEvent AfterScroll = { read=FAfterScroll, write=FAfterScroll };


// MyDB.cpp
#include "mydb.h"

// Assign "AfterScroll" a value in the constructor
__fastcall TMyDB::TMyDB(Classes::TComponent* AOwner):TDatabase(AOwner)
{
// Assign a function which handles the AfterScroll Event
// AfterScroll MUST HAVE A VALUE!
AfterScroll = AppAfterScroll;
}

// Just a function to point out how you can fire an AfterScroll Event
void __fastcall TMyDB::FireScrollEvent(TDataSet * DataSet)
{
AfterScroll(DataSet);
}


void __fastcall TMyDB::AppAfterScroll(TDataSet * DataSet)
{
/* This Function MUST EXIST. Its the default handler for the AfterScroll event*/
/* If AfterScroll is overridden. i.e. "AfterScroll = AnOtherFunction" this Function will be bypassed */
}