[Last Call] Learn about multicloud storage options and how to improve your company's cloud strategy. Register Now

x
?
Solved

Pointers to a function in Delphi?

Posted on 2008-06-10
7
Medium Priority
?
197 Views
Last Modified: 2010-05-18
I have an object, that sometimes needs to make a call to a function, and that function can be one of many. So i need to be able to tell the object what function it should use "this time". How do i:

(1) Make a var that holds the adress to a function.

(2) Tell the object what adress the function now have.

Im thinking like this:

// the function
function MyValue : integer
begin
result = 10;
end;

// the objec

procedure MyObject.SetFunction (p : funcpointer);


begin
       use p, how?
end;
0
Comment
Question by:Sunsales
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
  • 2
  • 2
  • +1
7 Comments
 
LVL 28

Accepted Solution

by:
2266180 earned 2000 total points
ID: 21753913

type
  TFunction=function:integer;
 
var f:TFunction;
 
function MyValue : integer;
begin
  result := 10;
end;
 
procedure TForm1.FormCreate(Sender: TObject);
begin
  f:=@myvalue;
  showmessage(inttostr(f));
end;

Open in new window

0
 

Author Comment

by:Sunsales
ID: 21754325
Thanx, but:

(1) I have no type "tfunction". Unknown to Delphi.

(2) In form create i need to have a variable storing the function. FormCreate dont know what variant im using. It can be MyValue1 or Myvalue2 or a complete different function...
0
 
LVL 13

Expert Comment

by:ThievingSix
ID: 21754418
*Points to "type TFunction=function:integer;"*

You define the TFunction yourself.
0
Concerto Cloud for Software Providers & ISVs

Can Concerto Cloud Services help you focus on evolving your application offerings, while delivering the best cloud experience to your customers? From DevOps to revenue models and customer support, the answer is yes!

Learn how Concerto can help you.

 
LVL 28

Expert Comment

by:2266180
ID: 21754425
(1) - it's only 15 lines of code. can't you pay more attention? I declared it for you

(2) - I don't understand your problem. declare your variable wherever you want.
0
 
LVL 13

Expert Comment

by:ThievingSix
ID: 21755019
Let's try this:
unit Unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;
 
type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
type
  TFunction = Function(Input: Integer): Integer;
 
var
  Form1 : TForm1;
  FunctionToCall : TFunction;
 
implementation
 
{$R *.dfm}
 
 
function ThisisFunctionA(Input: Integer): Integer;
begin
  Result := Input - 1;
end;
 
function ThisisFunctionB(Input: Integer): Integer;
begin
  Result := Input + 1;
end;
 
procedure TForm1.FormCreate(Sender: TObject);
begin
  FunctionToCall := @ThisisFunctionA;
end;
 
procedure TForm1.Button1Click(Sender: TObject);
begin
  ShowMessage(IntToStr(FunctionToCall(1)));
  FunctionToCall := @ThisisFunctionB;
  ShowMessage(IntToStr(FunctionToCall(1)));
end;
 
end.

Open in new window

0
 
LVL 38

Expert Comment

by:Geert Gruwez
ID: 21756659
guess you want to use methods instead of ordinary procedures ?

button 1 changes the value with 5

button 2 changes the proc called to function A

button 3 changes the proc called to function B
unit Unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;
 
type
  TFunction = Function(Input: Integer): Integer of object;
 
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  private
    FunctionToCall: TFunction;
    fValue: integer;
    function ThisisFunctionA(Delta: Integer): Integer;
    function ThisisFunctionB(Delta: Integer): Integer;
  public
    property aValue: integer read fValue write fValue;
  end;
 
var
  Form1 : TForm1;
 
implementation
 
{$R *.dfm}
 
 
function TForm1.ThisisFunctionA(Delta: Integer): Integer;
begin
  Result := fValue - Delta;
end;
 
function TForm1.ThisisFunctionB(Delta: Integer): Integer;
begin
  Result := fValue + Delta;
end;
 
procedure TForm1.FormCreate(Sender: TObject);
begin
  fValue := 100;
  FunctionToCall := ThisisFunctionA;
end;
 
procedure TForm1.Button1Click(Sender: TObject);
begin
  FunctionToCall(5);
  ShowMessage(IntToStr(AValue));
end;
 
procedure TForm1.Button2Click(Sender: TObject);
begin
  FunctionToCall := ThisisFunctionA;
end;
 
procedure TForm1.Button3Click(Sender: TObject);
begin
  FunctionToCall := ThisisFunctionB;
end;
 
end.

Open in new window

0
 

Author Comment

by:Sunsales
ID: 21760362
Thanx all, first example is god (all are) , i only sleep a few hours so i not c...
0

Featured Post

Concerto Cloud for Software Providers & ISVs

Can Concerto Cloud Services help you focus on evolving your application offerings, while delivering the best cloud experience to your customers? From DevOps to revenue models and customer support, the answer is yes!

Learn how Concerto can help you.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

In this tutorial I will show you how to use the Windows Speech API in Delphi. I will only cover basic functions such as text to speech and controlling the speed of the speech. SAPI Installation First you need to install the SAPI type library, th…
Creating an auto free TStringList The TStringList is a basic and frequently used object in Delphi. On many occasions, you may want to create a temporary list, process some items in the list and be done with the list. In such cases, you have to…
Sometimes it takes a new vantage point, apart from our everyday security practices, to truly see our Active Directory (AD) vulnerabilities. We get used to implementing the same techniques and checking the same areas for a breach. This pattern can re…
In a question here at Experts Exchange (https://www.experts-exchange.com/questions/29062564/Adobe-acrobat-reader-DC.html), a member asked how to create a signature in Adobe Acrobat Reader DC (the free Reader product, not the paid, full Acrobat produ…
Suggested Courses

650 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question