Inherit event procedure

[xenon54]

Hi, All!

Code: Pascal  [Select][+][-]

1.  
2. type
3.  
4.   TMyEvent = procedure(Sender: TObject) of object;
5.  
6.   TNewClass = class(TObject)
7.  
8.   end;
9.  
10.   TAClass = class
11.     private
12.       FOnEvent : TMyEvent;
13.  
14.     public
15.       property OnEvent : TMyEvent read FOnEvent write FOnEvent;
16.   end;
17.  
18.  
19.   SomeVar : TAClass;
20.  
21.   ...
22.  
23. begin
24.  
25.   ...
26.  
27.   SomeVar := TAClass.Create;
28.   SomeVar.OnEvent := @onEv;
29.  
30.   ...
31.  
32.   procedure TForm1.onEv(Sender: TNewClass);
33.   begin
34.  
35.   end;  
36.  
37.  

In this example copiller shows me error

Code: Pascal  [Select][+][-]

1. Error: Incompatible types: got "<procedure variable type of procedure(TObject) of object;Register>" expected "<procedure variable type of procedure(TNewClass ) of object;Register>"
2.  

What to do with this?

I dont want to do any like this in any usage of this...

Code: Pascal  [Select][+][-]

1.  
2.   procedure TForm1.onEv(Sender: TObject);
3.   var
4.     a : TNewClass;
5.   begin
6.  
7.     a := TNewClass(Sender);
8.  
9.   end;  
10.  
11.  
12.  

[howardpc]

In the declaration of TForm1 you have to declare the procedure with exactly the same signature:

Code: Pascal  [Select][+][-]

1.   TForm1 = class(TForm)
2.     procedure BlahBlah;
3.     ...
4.   private
5.     ...
6.   public
7.     procedure OnEv(Sender: TObject);
8.   end;

Only then can you write in some other TForm1 method

Code: Pascal  [Select][+][-]

1. SomeVar.OnEvent := @onEv;

 
BTW, what you call TMyEvent is called TNotifyEvent everywhere else in the LCL.

Why the duplication?

[xenon54]

In the declaration of TForm1 you have to declare the procedure with exactly the same signature:

Code: Pascal  [Select][+][-]

1.   TForm1 = class(TForm)
2.     procedure BlahBlah;
3.     ...
4.   private
5.     ...
6.   public
7.     procedure OnEv(Sender: TObject);
8.   end;

Only then can you write in some other TForm1 method

Code: Pascal  [Select][+][-]

1. SomeVar.OnEvent := @onEv;

 
BTW, what you call TMyEvent is called TNotifyEvent everywhere else in the LCL.

Why the duplication?

Thx for your reply, howardpc.

Duplication is just for example.

Maybe i m bad to understand my problem. Your reply about blahblah procedure unclear for me.

I meant that I would like to use the inherited type of class as Event param, but compiller gives me error.


Maybe a real example is better.


I use LNet component TLTcp in console application.
There is OnReceive event in this class. And as param in that procedure(event) have (aSocket : TLSocket).
I have inherited class TMySocket from TLSocket whit some new properties and methods.

And when i want to declare OnReceive event with my class as param, i got error.


I can do this

Code: Pascal  [Select][+][-]

1. procedure TSomeApplication.OnReceive(aSocket : TLsocket);
2. var
3.   t : TMySocket;
4. begin
5.   t := TMySocket(aSocket);
6.   ...
7. end;
8.  

but, its not elegant from me. Is there any way to do this right?

[lucamar]

The problem in your first post is here:

Code: Pascal  [Select][+][-]

1.   procedure TForm1.onEv(Sender: TNewClass);

As declared the event handler must have a TObject as parameter; otherwise you're trying to assign incompatible types.

Note that, though I advice seriously against it, you can always use absolute to hard-cast the passed object, so you could do, for example:

Code: Pascal  [Select][+][-]

1. procedure TForm1.onEv(Sender: TObject);
2. var
3.   NewObject: TMyClass absolute Sender;
4. begin
5.   NewObject.SomeMyClassMethod();
6.   {... etc ...}
7. end;

[xenon54]

The problem in your first post is here:

Code: Pascal  [Select][+][-]

1.   procedure TForm1.onEv(Sender: TNewClass);

As declared the event handler must have a TObject as parameter; otherwise you're trying to assign incompatible types.

Note that, though I advice seriously against it, you can always use absolute to hard-cast the passed object, so you could do, for example:

Code: Pascal  [Select][+][-]

1. procedure TForm1.onEv(Sender: TObject);
2. var
3.   NewObject: TMyClass absolute Sender;
4. begin
5.   NewObject.SomeMyClassMethod();
6.   {... etc ...}
7. end;

And what the diference btw

Code: Pascal  [Select][+][-]

1.  
2. procedure TForm1.onEv(Sender: TObject);
3. var
4.   NewObject: TMyClass absolute Sender;
5. begin
6.   NewObject.SomeMyClassMethod();
7.   {... etc ...}
8. end;
9.  
10.  

and

Code: Pascal  [Select][+][-]

1.  
2. procedure TForm1.onEv(Sender: TObject);
3. var
4.   NewObject: TMyClass;
5. begin
6.   NewObject := TMyClass(Sender);
7.   {... etc ...}
8. end;
9.  
10.  

?

[lucamar]

Very little. Basically you save up one line. But note that the more correct, safest way is to do something like:

Code: Pascal  [Select][+][-]

1. procedure TForm1.onEv(Sender: TObject);
2. var
3.   NewObject: TMyClass;
4. begin
5.   if Sender.InheritsFrom(TMyClass) then begin
6.     NewObject := TMyClass(Sender);
7.     {... etc ...}
8.   end;
9. end;

or

Code: Pascal  [Select][+][-]

1. procedure TForm1.onEv(Sender: TObject);
2. var
3.   NewObject: TMyClass;
4. begin
5.   if Sender is TMyClass then begin
6.     NewObject := TMyClass(Sender);
7.     {... etc ...}
8.   end;
9. end;

or, if you don't mind the ocassional error:

Code: Pascal  [Select][+][-]

1. procedure TForm1.onEv(Sender: TObject);
2. var
3.   NewObject: TMyClass;
4. begin
5.   NewObject := Sender as TMyClass;
6.   {... etc ...}
7. end;

[xenon54]

Very little. Basically you save up one line. But note that the more correct, safest way is to do something like:

Code: Pascal  [Select][+][-]

1. procedure TForm1.onEv(Sender: TObject);
2. var
3.   NewObject: TMyClass;
4. begin
5.   if Sender.InheritsFrom(TMyClass) then begin
6.     NewObject := TMyClass(Sender);
7.     {... etc ...}
8.   end;
9. end;

or

Code: Pascal  [Select][+][-]

1. procedure TForm1.onEv(Sender: TObject);
2. var
3.   NewObject: TMyClass;
4. begin
5.   if Sender is TMyClass then begin
6.     NewObject := TMyClass(Sender);
7.     {... etc ...}
8.   end;
9. end;

or, if you don't mind the ocassional error:

Code: Pascal  [Select][+][-]

1. procedure TForm1.onEv(Sender: TObject);
2. var
3.   NewObject: TMyClass;
4. begin
5.   NewObject := Sender as TMyClass;
6.   {... etc ...}
7. end;

Thx for reply. In my case, i totally know that my class is inherits from sender.

I just search way to override param class.

[PascalDragon]

I just search way to override param class.

You simply can't. If the event is declared as procedure(Sender: TObject) of object, then you must give it a method declared as procedure BlaBla(Sender: TObject). And if it's declared as procedure(Socket: TLSocket) of object, then you must use a method declared as procedure BlaBla(Socket: TLSocket). If you want something else then you have to cast (be it with a hard cast or an absolute).