[Solved] Destructor is giving me error

[nikel]

Hello, I'm trying to delete a stringlist in my child class. I attached the screenshot of the error. Here's my code:

Code: Pascal  [Select][+][-]

1. type
2.  
3.   { TMain }
4.  
5.   TMain = class
6.   protected
7.     procedure DoRun;
8.   public
9.     constructor Create();
10.     destructor Destroy;
11.     procedure WriteHelp(Ver: shortstring); virtual;
12. ...
13.  
14. type
15.   TParameterHandler = class(TMain)
16.   private
17.     ListOfParameters    : TStringList;
18.   public
19.     constructor Create();
20.     destructor Destroy;
21.  
22.     function CreateIndex(Directory: string): Boolean;
23. ...
24.  
25. destructor TParameterHandler.Destroy;
26. begin // This line is giving me error
27.   inherited Destroy;
28.   ListOfParameters:=nil;
29.   ListOfParameters.Free;
30. end;

How can I fix this error?

[egsuh]

You shoulld add "override" to all destroy destructors, as all classes are descendant of TObject.
And you should order in following order

Code: Pascal  [Select][+][-]

1. destructor TParameterHandler.Destroy;
2. begin // This line is giving me error
3.   ListOfParameters.Free;
4.   ListOfParameters:=nil;  // this is not necessary
5.  
6.   inherited Destroy;
7.  
8. end;

[nikel]

That worked fine. Thank you for your help.

[egsuh]

Good to hear that the issue has been solved. To explain a little more,

Code: Pascal  [Select][+][-]

1. destructor TParameterHandler.Destroy;
2. begin // This line is giving me error
3.   inherited Destroy;    //------ > this destroys object itself, and so nothing is left.
4.   ListOfParameters:=nil;  
5.   ListOfParameters.Free;   // --> even though "inherited destroy" had not been executed, you have set ListOfParameters to nil, and you are calling nil.Free, which is error.
6. end;