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Erik Doekes
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 Posted: Wed Jan 19, 2005 7:46 am Post subject: Pass event function as constructor parameter? |
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Hello!
-Is it possible to pass a function name as a parameter to a class
constructor which then can set the OnMoved property of one of the VCL
attributes of the class?
-How do I do that? (I mean, I can set XX->OnMoved=Form1->SplitterMoved, but
I don't know the "type" of a function, which would be required to be able to
pass it as an argument)
Maybe it's not even relevant, but for your background information here is my
problem in more detail:
I've created a VCL-based class called TransactionRow, which consists of a
panel with editing fields and splitters.
The instances of TransactionRow will be placed below each other on the
screen (as well as contained in a TList in the main form MainForm).
Now, the splitters have to interact - if one is moved, then all the others
do as well, as well as do the splitters of one instance of another class,
HeaderPanel. So I wrote a function instantiateSplitter which was called by
the constructors of both TransactionRow and HeaderPanel. Parameters are a
pointer to the spliter, the owner component, the parent control and its left
position. Among the properties set were Parent, Left and Minsize but also
OnMoved = MainForm->SplitterMoved.
So far so good. But now, I want to separate out TransactionRow into its own
unit file and here the problems start. TransactionRow.cpp will be called
before the main form has been instantiated and thus BC++ cannot find
MainForm. Placing the function instantiateSplitter inside the main unit will
not help either, since I then have to call MainForm->instantiateSplitter
from the TransactionRow class constructor.
Should I abandon my thoughts of separating out TransactionRow.cpp? I don't
like the idea of having to call a function from the main form each time a
TransactionRow is created.
An alternative might be to send the function OnMoved as a parameter to the
constructor of TransactionRow. That's an idea I really like, but don't know
how to do.
Even if you think I should use something else like e.g. a ListView, I would
appreciate a specific answer to the function parameter question.
Grateful for your help on this one,
/Erik
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Hans Galema
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| Posted: Wed Jan 19, 2005 12:29 pm Post subject: Re: Pass event function as constructor parameter? |
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Erik Doekes wrote:
| Quote: | -Is it possible to pass a function name as a parameter to a class
constructor which then can set the OnMoved property of one of the VCL
attributes of the class?
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Yes. Demo follows where the constructor of TForm2 takes a function
of an instance of TForm1 as parameter:
Unit1.cpp
void __fastcall TForm1::Button1Click(TObject *Sender)
{
ShowMessage ( "Hello this is Button1");
}
void __fastcall TForm1::Button2Click(TObject *Sender)
{
TForm2 *Form2 = new TForm2 ( this, &Button1Click);
Form2->Show();
}
Unit2.hpp
typedef void __fastcall (__closure *TFunc)(TObject *Sender);
class TForm2 : public TForm
{
__published: // IDE-managed Components
TButton *Button1;
private: // User declarations
public: // User declarations
__fastcall TForm2(TComponent* Owner);
__fastcall TForm2(TComponent* Owner, TFunc );
};
Unit2.cpp:
__fastcall TForm2::TForm2(TComponent* Owner, TFunc Func)
: TForm(Owner)
{
Button1->OnClick = Func;
}
Hans.
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Remy Lebeau (TeamB)
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| Posted: Wed Jan 19, 2005 6:15 pm Post subject: Re: Pass event function as constructor parameter? |
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"Hans Galema" <notused (AT) notused (DOT) nl> wrote
| Quote: | typedef void __fastcall (__closure *TFunc)(TObject *Sender);
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Use the VCL's existing TNotifyEvent type instead. Especilly since the
OnClick event is declared as a TNotifyEvent in the first place.
Gambit
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Hans Galema
Guest
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| Posted: Thu Jan 20, 2005 12:54 pm Post subject: Re: Pass event function as constructor parameter? |
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Remy Lebeau (TeamB) wrote:
| Quote: | typedef void __fastcall (__closure *TFunc)(TObject *Sender);
Use the VCL's existing TNotifyEvent type instead. Especilly since the
OnClick event is declared as a TNotifyEvent in the first place.
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First did that indeed. But could not get it working so I decided
to do it from scratch. It was the & in &Button1Click which
I had not forseen and am still amazed of. Indeed TNotifyEvent
is the same typedef.
Hans.
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