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Mattias Andersson · Guest

Hi all,

I'm writing my own custom streaming routines for TPersistent based objects
in Delphi 7.

Now, it seems that I've come across a glitch in one of the streaming
functions. The function that causes the problem is 'IsDefaultPropertyValue',
which I believe is used to highlight non-default values in the Object
Inspector. Apparently this is also one of two functions that were added to
the Classes unit in Delphi 7.

The problem is a nil-pointer dereference error inside IsDefaultMethodProp at
the following line:

Result := (Value.Code = DefaultCode) or
((Value.Code <> nil) and (LookupRoot.MethodName(Value.Code) = ''));

I think an additional test is needed here to ensure that LookupRoot is
actually assigned.

See the test case below in order to reproduce the problem.

Do you think that this should be reported to QC?

Kind regards,

Mattias Andersson

uses
Classes, TypInfo;

type
TMyClass = class(TPersistent)
private
FOnEvent: TNotifyEvent;
procedure DummyMethod(Sender: TObject);
published
property OnEvent: TNotifyEvent read FOnEvent write FOnEvent;
end;

procedure TMyClass.DummyMethod(Sender: TObject);
begin
end;

procedure TForm1.Button1Click(Sender: TObject);
var
MyClass: TMyClass;
PropInfo: PPropInfo;
begin
MyClass := TMyClass.Create;
try
MyClass.OnEvent := MyClass.DummyMethod;
PropInfo := GetPropInfo(MyClass, 'OnEvent');
IsDefaultPropertyValue(MyClass, PropInfo, nil);
finally
MyClass.Free;
end;
end;

Sebastian Modersohn · Guest