Function pointer problem

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3 total messages Started by btm Tue, 14 Sep 1999 00:00

#15

Author: btm
Date: Tue, 14 Sep 1999 00:00

52 lines
2074 bytes

In a general form used by several other forms I defined a function
reference like this [Delphi 1]:

      type
        TCheckFunc = function (FldNr: integer): Boolean;
        TSetParam = class(TForm)
          ....      
        public
          CheckStatus: TCheckFunc;
        end;

In several of my forms I now want to do something like this:

      type
        TForm1 = class(TForm)
          Button1: TButton;
          procedure Button1Click(Sender: TObject);
        private
        public
          function Form1Check (FldNr: integer): Boolean;
        end;

      implementation
      {$R *.DFM}

      procedure TForm1.Button1Click(Sender: TObject);
      var frm: TSetParam;
      begin
      frm:=TSetParam.create(self);
      frm.CheckStatus:=Form1Check;    { doesn't work! WHY? }
      frm.showmodal;
      frm.Release;
      end;


      function TForm1.Form1Check (FldNr: integer): Boolean;
      begin
      { set to True or False according to specific conditions : }
      result:=True;  
      end;


Alas, there is something wrong with this... The compiler says that the
assignment
      frm.CheckStatus:=MyCheck;
is an invalid function/procedure reference. What's wrong with this?



Thanks for any hints!

Thomas

Re: Function pointer problem

#16

Author: Liz Kimber
Date: Tue, 14 Sep 1999 00:00

20 lines
1434 bytes

>      type
>        TCheckFunc = function (FldNr: integer): Boolean;
>        TSetParam = class(TForm)
>          ....      
>        public
>          CheckStatus: TCheckFunc;
>        end;

You have declaed the CheckStatus to need something returning a type of
TCheckFunc..

You actually should have set it as boolean according to the procuedure
you made here

>
>      function TForm1.Form1Check (FldNr: integer): Boolean;
>      begin
>      { set to True or False according to specific conditions : }
>      result:=True;  
>      end;

Re: Function pointer problem

#17

Author: Bruce Roberts
Date: Tue, 14 Sep 1999 00:00

48 lines
2108 bytes

btm <btm@gmx.net> wrote in message
news:37de2a8b.335943@news.spectraweb.ch...
> In a general form used by several other forms I defined a function
> reference like this [Delphi 1]:
>
>       type
>         TCheckFunc = function (FldNr: integer): Boolean;

This declares a function type that is declared at the main level of a unit,
not a class method.

>         TSetParam = class(TForm)
>           ....
>         public
>           CheckStatus: TCheckFunc;
>         end;
>
> In several of my forms I now want to do something like this:
>
>       type
>         TForm1 = class(TForm)
>           Button1: TButton;
>           procedure Button1Click(Sender: TObject);
>         private
>         public
>           function Form1Check (FldNr: integer): Boolean;

This is a class function.

>         end;
>

You can either change your type definition to

         TCheckFunc = function (FldNr: integer): Boolean of object;

or remove Form1Check from the form declaration and place it in the main body
of the unit, e.g.

type
    form1 = . . .
        end;

    function Form1Check . . .

Either will correct the error. However in this case you probably want to
change the function type definition (the first suggestion).

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