CODEWITHSUNDEEP
delphi
user401247
user401247

Reputation:

Objects in a list needs to access parent list properties

This is a design question for Delphi.

An Object A contains a set of variables and at the same time stores a list of Objects of type B. Objects of type B need to access the common variables in the container Object A. One option is for Objects B to hold a reference to the container Object A but this seems to result in storing the reference to A as a TObject and casing each time to Object A in order to access the variables. Any other possible design solutions?

Object B
  // Possible solution
  ref to Object A

Object A
  x : integer
  list of B

Each B needs access to x

Upvotes: 1

Views: 466

Answers (1)

David Heffernan
David Heffernan

Reputation: 613352

You need a forward type declaration:

type
  TContainer = class; // forward declaration

  TItem = class
  private
    FContainer: TContainer;
    ....
  end;

  TContainer = class
  private
    // list of items
  end;

The forward declaration can be either the container or the item, it doesn't much matter which.

Read all about this in the docs: http://docwiki.embarcadero.com/RADStudio/en/Classes_and_Objects#Forward_Declarations_and_Mutually_Dependent_Classes

Upvotes: 2

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