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Josep Seto · Guest

Hello,

To simplify the action of a Cancel button in a form wich modifies an object
inherited from TComponent I use the following strategy.

__fastcall TFormA::TFormA(TComponent *Owner, TMyComponent *pMyComponent) :
TForm(Owner)
{
myComponent=pMyComponent;
}

void __fastcall TFormA::FormShow(TObject *Sender)
{
//Update form controls from myComponent properties
myComponent->Backup();
}

void __fastcall TFormA::btCancelClick(TObject *Sender)
{
myComponent->Restore();
Close();
}

void __fastcall TFormA::btOkClick(TObject *Sender)
{
//myComponent properties updated on the fly, so nothing to do here
Close();
}

void __fastcall TMyComponent::Backup()
{
memStream->Seek(0,soFromBeginning);
memStream->WriteComponent(this);
}

void __fastcall TMyComponent::Restore()
{
memStream->Seek(0,soFromBeginning);
memStream->ReadComponent(this);
}

What i'm doing is making a backup of the component properties into a memory
stream before anything is changed in the dialog and if the user decides to
discard the changes, then I restore the original state of the component
reading the component from the stream.
The problem is that it only works if the properties are different to the
default values after saving the component in the stream. That is, the first
time the form is shown, lets say myProperty shows the default value of 0.
The user changes it to 1 (myComponent->myProperty=1) in some part of the
form, but then decides to cancel it pressing Cancel button. This will call
myComponent->Restore() to get back to the initial values. As at the begining
myProperty had the default value, it wasn't saved to the stream because it
had the default value, and when the component is read from the stream,
myProperty is not modified because it wan't saved to the stream and
therefore not readed.

Is there any way to force writing the property to a stream? I tried nodefaul
modifier but does not work. Setting the modifier default to a value probably
will work but it is not very elegant and can introduce coding errors.

I know there are plenty of different approaches to the "Cancel behaviour"
but my approach is very useful (if it works, of course) because I have
plenty of TMyComponent derived classes and this simplifies a lot the
development.

Thanks

Josep

Remy Lebeau (TeamB) · Guest

"Josep Seto" <remove-jseto (AT) vodafone (DOT) es> wrote in message
news:4606cc9e (AT) newsgroups (DOT) borland.com...

Horst Reichert · Guest