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René Wilhelmy
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 Posted: Tue Dec 16, 2003 7:27 pm Post subject: Need tip to create undo with TObject derived |
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Hi,
I'm looking for any suggestions about undo data changes using my derived
objects, like the one (so usefull!) found in CBuilder example.
I read little bit about the use of the type Variant.
Is it a good way to track down the modifications of the properties and
values around my Class?
Thanks,
rene
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Remy Lebeau (TeamB)
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| Posted: Tue Dec 16, 2003 9:07 pm Post subject: Re: Need tip to create undo with TObject derived |
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"René Wilhelmy" <r.wil (AT) sympatico (DOT) ca> wrote
| Quote: | I'm looking for any suggestions about undo data changes
using my derived objects, like the one (so usefull!) found
in CBuilder example.
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What exactly are you trying to accomplish? Please provide more details,
your description is very vague.
Gambit
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René Wilhelmy
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| Posted: Wed Dec 17, 2003 4:44 pm Post subject: Re: Need tip to create undo with TObject derived |
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Thanks for your time Remy!
I'm developping a CAD application which use plenty of derived TObject,
TGraphicControl etc. So I want to track down all the real time user's
actions with the soft: like moving a control point (value X and Y),
adding or removing an object on the drawing etc., changing Properties on
a specific object; and giving to the user
the possibility to undo (or redo) one or multiple action(s) at anytime.
At first, my rough approach could be to use a TObjectList and adding on
it a special Class Object for each user's action, and which could point
properly to different modified value and hold the specific value at his
original state. So my first request is to know if a Variant can
correctly point to a Propertie and a VCL Class and of course if another
way could more appropriate...
Many thanks,
Rene Wilhelmy
Remy Lebeau (TeamB) a écrit:
| Quote: | "René Wilhelmy" <r.wil (AT) sympatico (DOT) ca> wrote in message
news:3FDF5C8C.3080200 (AT) sympatico (DOT) ca...
What exactly are you trying to accomplish? Please provide more details,
your description is very vague.
Gambit
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Remy Lebeau (TeamB)
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| Posted: Wed Dec 17, 2003 6:42 pm Post subject: Re: Need tip to create undo with TObject derived |
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"René Wilhelmy" <r.wil (AT) sympatico (DOT) ca> wrote
| Quote: | I want to track down all the real time user's actions with the soft:
like moving a control point (value X and Y), adding or removing
an object on the drawing etc., changing Properties on a specific
object; and giving to the user the possibility to undo (or redo) one
or multiple action(s) at anytime.
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Since the VCL has no such provisions available, you will just have to
inclement your own system manually.
| Quote: | At first, my rough approach could be to use a TObjectList
and adding on it a special Class Object for each user's action
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That is one way to do it. Why use a TObjectList, though? That requires
your "special" class to be a TObject descendant, which is unnecessary for
what you are asking. You could just use a TList or STL container
(std::vector, std::deque, etc) instead.
| Quote: | So my first request is to know if a Variant can correctly
point to a Propertie
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Not to the property itself, no, only a copy of the value that it contains.
No.
I would not recommend using a Variant for what you ask anyway, even if it
did support it. I would instead suggest creating specialized classes for
each particular operation that you want to be able to undo, derived from an
abstract base class that has a virtual Undo() method that each descendant
overrides to perform the actual undo operations. That way, you can have a
list of base class pointers, and for each operation that supports undoing
since create an instance of the appropriate Undo class and add it to the
list. Then, when needed you can simply run through the list and call Undo()
for each operation desired, without actually knowing what the operation
actually is, and let polymorphism work for you in determine what actions
need to be performed.
For example (untested):
--- UndoClasses.h ---
class TUndoActionBase
{
public:
virtual void Undo() = 0;
};
TControlPointChangeUndo : public TUndoActionBase
{
private:
TControl *Control;
int PreviousX, PreviousY;
public:
TControlPointChangeUndo(TControl *AControl);
void Undo();
}
TAddObjectUndo : public TUndoActionBase
{
private:
TObject *Object;
public:
TAddObjectUndo(TObject *AObject);
void Undo();
}
#include <TypInfo.hpp>
// note - this class only supports undoing *published* properties.
// if you need to undo *public* properties instead, then you will
// have to come up with your own mechanism for it.
TChangePropertyUndo : public TUndoActionBase
{
private:
TObject *Object;
PPropInfo PropInfo;
Variant PreviousValue;
public:
TChangePropertyUndo(TObject *AObject, const AnsiString &PropName);
void Undo();
}
--- UndoClasses.cpp ---
TControlPointChangeUndo::TControlPointChangeUndo(TControl *AControl)
: TUndoActionBase()
{
Control = AControl;
PreviousX = Control->Left;
PreviousY = Control->Top;
}
void TControlPointChangeUndo::Undo()
{
Control->Left = PreviousX;
Control->Top = PreviousY;
}
TAddObjectUndo::TAddObjectUndo(TObject *AObject)
: TUndoActionBase()
{
Object = AObject;
}
void TAddObjectUndo::Undo()
{
delete Object;
}
TChangePropertyUndo::TChangePropertyUndo(TObject *AObject, const
AnsiString &PropName)
: TUndoActionBase()
{
Object = AObject;
PropInfo = GetPropInfo(Object, PropName);
if( PropInfo )
PreviousValue = GetVariantProp(Object, PropInfo);
}
void TChangePropertyUndo::Undo()
{
if( PropInfo )
SetVariantProp(Object, PropInfo, PreviousValue);
}
Then, your main code can do something like the following:
#1: using TList:
#include "UndoClasses.h"
TList *UndoList = new TList;
//...
TMyObject *obj = new TMyObject;
UndoList->Add(new TAddObjectUndo(obj));
//...
UndoList->Add(new TControlPointChangeUndo(obj));
obj->Left = NewLeft;
obj->Top = NewTop;
//...
UndoList->Add(new TChangePropertyUndo(obj, "SomeProperty"));
obj->SomeProperty = NewValue;
//...
while( UndoList->Count )
{
TUndoActionBase *pAction = (TUndoActionBase*)
UndoList->Items[UndoList->Count-1];
UndoList->Delete(UndoList->Count-1);
pAction->Undo();
delete pAction;
}
//...
delete UndoList;
#2: Using std::vector
#include "UndoClasses.h"
#include <vector>
std::vector<TUndoActionBase*> UndoList;
//...
TMyObject *obj = new TMyObject;
UndoList.push_back(new TAddObjectUndo(obj));
//...
UndoList.push_back(new TControlPointChangeUndo(obj));
obj->Left = NewLeft;
obj->Top = NewTop;
//...
UndoList.push_back(new TChangePropertyUndo(obj, "SomeProperty"));
obj->SomeProperty = NewValue;
//...
while( !UndoList.empty() )
{
std::vector<TUndoActionBase*>::iterator iter = UndoList.back();
TUndoActionBase *pAction = (*iter);
UndoList.pop_back();
pAction->Undo();
delete pAction;
}
Gambit
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René Wilhelmy
Guest
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| Posted: Wed Dec 17, 2003 9:10 pm Post subject: Re: Need tip to create undo with TObject derived |
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Again thank you very much Remy!
I appreciate a lot the vector aspect and the use of PPropInfo and the
methods of TPropertyEditor which are my missing pieces!
Rene Wilhelmy
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