Em 28/8/2012 09:15, michael.vancann...@wisa.be escreveu:
On Tue, 28 Aug 2012, Luiz Americo Pereira Camara wrote:
Why not let TFPObservedOperation as integer and define constants.
It could define a constant like ooUser = 32
Below ooUser is reserved for future default constants
Above ooUser could be added custom messages
This is how LCL messages works
Exactly because it is not meant as a general messaging interface, and
I want the interface to reflect this.
There is a clear intended use case: Mainly notification of changes.
This is the purpose i intend to use (replace my implementation).
Basically is a tree structure that needs to be observed. To avoid
performance problems like having to parse all the tree when a change
occurs i defined actions when a Child is added, deleted or inserted.
To be clear what i would need to do with the current approach:
const
ChildAdded = 1;
type
TMyNotifyInfo = record
NType: Integer;
NData: Pointer;
end;
PMyNotifyInfo = ^TMyNotifyInfo;
//notify
procedure TMyObserved.Changed;
var
R: TMyNotifyInfo;
begin
R.NType := ChildAdded;
R.NData := ChildItemObject;
FPONotifyObservers(Self,ooCustom,@R);
end;
//observe
procedure TMyObserver.FPOObservedChanged(ASender : TObject; Operation :
TFPObservedOperation; Data : Pointer);
var
R: PMyNotifyInfo;
begin
if Operation = ooCustom then
begin
R := PMyNotifyInfo(Data);
if R^.Ntype = ChildAdded then
DoChildAdd(R^.NData);
end;
end;
compare with my proposed solution of defining the type as integer:
const
ooChildAdded = ooUser + 1;
//notify
procedure TMyObserved.Changed;
begin
FPONotifyObservers(Self, ooChildAdded, ChildItemObject);
end;
//observe
procedure TMyObserver.FPOObservedChanged(ASender : TObject; Operation :
TFPObservedOperation; Data : Pointer);
begin
if Operation = ooChildAdded then
begin
DoChildAdd(Data);
end;
end;
Simpler, less code, less memory use, extensible.
All that with just changing the TFPObservedOperation to a Integer or
word type
IMO such feature at a low level class should be usable in the most use
cases, otherwise it will have a half observer support.
My proposition does not increase complexity of the code, nor any type of
overhead with the above gains.
Can you point the drawbacks?
Luiz
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