Default for published property

[chkaufmann 17]

I have a custom control and defined the following published properties:

 

    property MaxValue: Integer read FMaxValue write SetMaxValue default High(Integer);
    property MinValue: Integer read FMinValue write SetMinValue default Low(Integer);

It works fine for MaxValue, but for MinValue I always get this in my dfm files:

 

      MinValue = -2147483648

 

Are there limitations for default values and if yes, where can I find these?

 

Christian

 

[Lars Fosdal 1792]

Low(Integer) - assuming 32-bit Integer - will always be -2,147,483,648

What value were you expecting to see? Zero?  Then you need to use Default 0 - or type Cardinal instead of Integer.

Note that using a Cardinal can introduce challenges with regards to math operations that may cause a signed result such as (Small.Minvalue - Big.MinValue) < 0

[chkaufmann 17]

I except the default not to be written to the DFM at all. It works for High(Integer) but it looks like it doesn't for Low(Integer).

 

Christian

[Stefan Glienke 2002]

The TypeInfo uses the value $80000000 to indicate that this property has no default value.

That unfortunately overlaps with Low(Integer).

 

You have to use the stored keyword:

 

property MinValue: Integer read FMinValue write SetMinValue stored IsMinValueStored;

function TMyComponent.IsMinValueStored: Boolean;
begin
  Result := FMinValue <> Low(Integer)
end;

 

Edited November 21, 2019 by Stefan Glienke

[chkaufmann 17]

Thanks for the solution.

Christian