Entry

Delphi: Procedure: Function: Dynamic: Simple: How pass function method as parameter: 1 parameter?

Feb 23rd, 2004 15:18
Knud van Eeden,

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--- Knud van Eeden --- 23 February 2004 - 11:48 pm -------------------

Delphi: Procedure: Function: Dynamic: Simple: How pass function method 
as parameter: 1 parameter?

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The trick is to use '= Function of Object' (instead of '= Function').

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Steps: Overview:

 1. Create a new application

 2. Put e.g. a button on the form

 3. Add the following text

     // this does the trick

     type TMyFunctionAsParameter = Function( s : string ): string of 
Object;

     var myfunctionasparameter : TMyFunctionAsParameter;

 4. -Create now one or more functions which have also one parameter of
     the same type as declared above (e.g. a string).

      function TForm1.FNTestOne( s : string ): string;
      begin
       result := 'FNTestOne gets: ' + s;
      end;

      function TForm1.FNTestTwo( s : string ): string;
      begin
       result := 'FNTestTwo gets: ' + s;
      end;

     and declare the function headers as usual in the
     interface section:

      function FNTestOne( s : string ): string;

      function FNTestTwo( s : string ): string;

 5. -Call then the corresponding function by passing
     the name of that function as a parameter by

     1. first assigning the name to the 'var' variable

     2. then calling that 'var' variable with some
        parameter

         myfunctionasparameter := FNTestOne;
         s := myfunctionasparameter( 'some string 1' );
         ShowMessage( s );

         myfunctionasparameter := FNTestTwo;
         s := myfunctionasparameter( 'some string 2' );
         ShowMessage( s );

 6. -So all together this becomes:

--- cut here ---------------------------------------------------------

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, 
Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    function FNTestOne( s : string ): string;
    function FNTestTwo( s : string ): string;

  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

function TForm1.FNTestOne( s : string ): string;
begin
 result := 'FNTestOne gets: ' + s;
end;

function TForm1.FNTestTwo( s : string ): string;
begin
 result := 'FNTestTwo gets: ' + s;
end;

procedure TForm1.Button1Click(Sender: TObject);
 type TMyFunctionAsParameter = Function( s : string ): string of 
Object;
 var myfunctionasparameter : TMyFunctionAsParameter;
 var s : string;
begin
 myfunctionasparameter := FNTestOne;
 s := myfunctionasparameter( 'some string 1' );
 ShowMessage( s );

 myfunctionasparameter := FNTestTwo;
 s := myfunctionasparameter( 'some string 2' );
 ShowMessage( s );
end;

end.

--- cut here ---------------------------------------------------------

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Internet: see also:

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Delphi: Procedure: Function: Dynamic: Can you give overview passing 
function/procedure as parameter?
http://www.faqts.com/knowledge_base/view.phtml/aid/28931/fid/175

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