Can a class create a class within itself?

[petejones]

Can a class create a class within itself? Here is the code:

type
    TParameter = class(TObject)
    private
      ParamValue: Variant;
      ParamType: TParameterType;
    end;

type
    TParameters = class
    public
      Items: specialize TFPGObjectList<TParameter>;
      constructor Create();
      procedure Add(ParameterValue: Variant; ParameterType: TParameterType);
    end;

I want the TParameters class to create the Items list when an instance of the TParameters class is created. Is this possible?

Thanks
Pete

[Thausand]

specialize:

Code: Pascal  [Select][+][-]

1. type
2.   TParameterList=specialize TFPGObjectList<TParameter>;
3.  

Create:

Code: Pascal  [Select][+][-]

1. constructor TParameters.Create;
2. begin
3.   inherited;
4.   Items:=TParameterList.Create;
5. end;
6.  

Free:

Code: Pascal  [Select][+][-]

1. destructor TParameters.Destroy;
2. begin
3.   Items.Free;
4. end;
5.  

How to add:

Code: Pascal  [Select][+][-]

1. procedure TParameters.Add(ParameterValue:Variant; ParameterType:TParameterType);
2. var
3.   Parameter:TParameter;
4. begin
5.   Parameter:=TParameter.Create;
6.   Parameter.ParamValue:=ParameterValue;
7.   Parameter.ParamType:=ParameterType;
8.   Items.Add(Parameter);
9. end;
10.  

[petejones]

Thanks 

[petejones]

I'm getting an error to do with the constructor - when I put a breakpoint on Items:=TParameterList.Create and step over that line, Items isn't set to anything and I get a SIGSEGV error when I attempt to add to Items.

Any ideas?

[howardpc]

My best idea is to get you to share a compilable project that gives the error.
Then others can pinpoint its cause quickly without have to guess or make assumptions about what the rest of your code might contain.

[petejones]

Good idea, I've attached a zip of the test project.

Cheers
Pete

[Thausand]

not good:

Code: Pascal  [Select][+][-]

1.   Parameters.Create;
2.   Parameters.Add('Test', TParameterType.TText);
3.   Parameters.Free;
4.  

better:

Code: Pascal  [Select][+][-]

1.   Parameters := TParameters.Create;
2.   Parameters.Add('Test', TParameterType.TText);
3.   Parameters.Free;
4.  

Is not point you ask how to create class ? Then you forget to do

[petejones]

Ah yes, thanks!

[howardpc]

While you can use generics, as you do, I think generics + variants is somewhat overkill.
I would simply use a TFPObjectList from contnrs unit.