Delphi Compiler Error
E2209 Field declarations not allowed in interface type
Reason for the Error & Solution
An interface has been encountered which contains definitions of fields; this is not permitted.
program Produce;
type
IBaseIntf = interface
FVar : Integer;
property Value : Integer read FVar write FVar;
end;
begin
end.
The desire above is to have a property which has a value associated with it. However, as interfaces can have no fields, this idea will not work.
program Solve;
IBaseIntf = interface
function Reader : Integer;
procedure Writer(a : Integer);
property Value : Integer read Reader write Writer;
end;
begin
end.
An elegant solution to the problem described above is to declare getter and setter procedures for the property. In this situation, any class implementing the interface must provide a method which will be used to access the data of the class.
