Delphi - 使用来自另一个单元的接口

Question

I am constantly getting the: Undeclared identifier for an interface type I have defined in another unit. Here is what I have:

unit Drawers;

interface

implementation

type

  IDrawer = interface
  ['{070B4742-89C6-4A69-80E2-9441F170F876}']
    procedure Draw();
  end;

end.

---

unit Field;

interface

uses
  Graphics, Classes, Drawers;

TField = class(TInterfacedObject, IField)
private
  FSymbolDrawer: IDrawer;

At FSymbolDrawer I get the complier error.

Of course I have the uses Drawers; in the unit where TField is defined.

What's this about?

Thank you

Answer 1

In the unit Drawers the type declaration of IDrawer has to be in the interface part of the unit. You have inserted it in the implementation part where it is only visible for in-unit declarations.

Here is the code:

unit Drawers;

interface

type

  IDrawer = interface
  ['{070B4742-89C6-4A69-80E2-9441F170F876}']
    procedure Draw();
  end;

implementation

end.

Answer 2

Which uses clause do you add Drawers to? It has to be in the interface uses clause (above the definition of TField that uses it).