Difference between revisions of "How To Use Interfaces"

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Copy the text below and it will demonstrate how to use [[Interfaces]] to write less code, avoid code repetition,..., this is a fully working program.
 
Copy the text below and it will demonstrate how to use [[Interfaces]] to write less code, avoid code repetition,..., this is a fully working program.
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<syntaxhighlight>{$mode objfpc}{$H+}{$interfaces com}
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>>this is a fully working program
 
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No, this code contains memory leaks and incorrect use of interfaces. Please pay attention to this
 
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<syntaxhighlight lang="pascal">
 
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program interfacesygenerics;
 
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{$mode objfpc}{$H+}
 
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const
 
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  STestInterface = '{3FB19775-F5FA-464C-B10C-D8137D742088}';
 
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type
 
type
 
   ITestInterface = interface
 
   ITestInterface = interface
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     [STestInterface]
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     ['{3FB19775-F5FA-464C-B10C-D8137D742088}']
 
     procedure DoSomething;
 
     procedure DoSomething;
 
     procedure DoItAll;
 
     procedure DoItAll;
 
   end;
 
   end;
  
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  { Base class Start }
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   TBaseObject = class(TInterfacedObject,ITestInterface)
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   TBaseObject = class(TInterfacedObject)
 
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    procedure DoAll;
 
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  end;
 
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  procedure TBaseObject.DoAll;
 
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  begin
 
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    Writeln('TBaseObject DoAll !');
 
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  end;
 
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  { Base class End }
 
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type
 
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  { THook Start}
 
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  //Interface implementation on a derived class
 
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  THook = class(TBaseObject, ITestInterface)
 
 
     procedure DoSomething;
 
     procedure DoSomething;
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    //Contrary to what is stated on the FPC reference manual
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     procedure DoItAll;
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    //it's now possible to use aliases to indicate
 
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    //interface implementations
 
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     procedure ITestInterface.DoItAll = DoAll;
 
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  end;
 
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  procedure THook.DoSomething;
 
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  begin
 
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    Writeln('THook Doing something !');
 
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  end;
 
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  { THook End}
 
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type
 
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  { TRealClass Start }
 
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  TRealClass = class(TBaseObject, ITestInterface)
 
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  private
 
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    FHook: ITestInterface;
 
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  public
 
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    constructor Create;
 
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    destructor Destroy; override;
 
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    //Here we tell the compiler that our class
 
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    //interface implementation is provided by
 
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    //a member field wich we initialize in this case
 
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    //on the constructor
 
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    property Hook: ITestInterface read FHook implements ITestInterface;
 
 
   end;
 
   end;
  
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   constructor TRealClass.Create;
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   procedure TBaseObject.DoSomething;
 
   begin
 
   begin
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     //Creating our interface implementor
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     Writeln('TBaseObject DoSomething !');
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    FHook := THook.Create;
 
 
   end;
 
   end;
  
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   destructor TRealClass.Destroy;
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   procedure TBaseObject.DoItAll;
 
   begin
 
   begin
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     //Releasing our interface implementor
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     Writeln('TBaseObject DoItAll !');
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    THook(FHook).Free;
 
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    inherited Destroy;
 
 
   end;
 
   end;
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  { TRealClass End }
 
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var
 
var
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  R: TRealClass;
 
 
   I: ITestInterface;
 
   I: ITestInterface;
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begin
 
begin
 
   Writeln('Using regular interfaces');
 
   Writeln('Using regular interfaces');
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   I := TBaseObject.Create as ITestInterface;
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   R := TRealClass.Create;
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   if I <> nil then
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  //callign the interfaced function directly
 
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  R.DoAll;
 
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  //Calling through the interface
 
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   if R.GetInterface(STestInterface, I) then
 
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  begin
 
 
     Writeln('Got interface OK. Calling it');
 
     Writeln('Got interface OK. Calling it');
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    I.DoSomething;
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  I.DoSomething;
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    I.DoItAll;
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  I.DoItAll;
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  end else
 
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    Writeln('Interface not implemented !');
 
 
end.
 
end.
 
</syntaxhighlight>
 
</syntaxhighlight>
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== See also ==
 
== See also ==
  

Revision as of 17:09, 5 October 2021

Copy the text below and it will demonstrate how to use Interfaces to write less code, avoid code repetition,..., this is a fully working program. 

{$mode objfpc}{$H+}{$interfaces com}
type
  ITestInterface = interface
    ['{3FB19775-F5FA-464C-B10C-D8137D742088}']
    procedure DoSomething;
    procedure DoItAll;
  end;

  TBaseObject = class(TInterfacedObject,ITestInterface)
    procedure DoSomething;
    procedure DoItAll;
  end;

  procedure TBaseObject.DoSomething;
  begin
    Writeln('TBaseObject DoSomething !');
  end;

  procedure TBaseObject.DoItAll;
  begin
    Writeln('TBaseObject DoItAll !');
  end;
var
  I: ITestInterface;
begin
  Writeln('Using regular interfaces');
  I := TBaseObject.Create as ITestInterface;
  if I <> nil then
    Writeln('Got interface OK. Calling it');
  I.DoSomething;
  I.DoItAll;
end.

See also

Retrieved from "http://wiki.freepascal.org/index.php?title=How_To_Use_Interfaces&oldid=147121"