Pointers to a function in Delphi?
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;
(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;
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*Points to "type TFunction=function:integer
You define the TFunction yourself.
You define the TFunction yourself.
(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.
(2) - I don't understand your problem. declare your variable wherever you want.
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
{$R *.dfm}
function ThisisFunctionA(Input: Integer): Integer;
begin
Result := Input - 1;
end;
function ThisisFunctionB(Input: Integer): Integer;
begin
Result := Input + 1;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
FunctionToCall := @ThisisFunctionA;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
ShowMessage(IntToStr(FunctionToCall(1)));
FunctionToCall := @ThisisFunctionB;
ShowMessage(IntToStr(FunctionToCall(1)));
end;
end.
guess you want to use methods instead of ordinary procedures ?
button 1 changes the value with 5
button 2 changes the proc called to function A
button 3 changes the proc called to function B
button 1 changes the value with 5
button 2 changes the proc called to function A
button 3 changes the proc called to function B
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
type
TFunction = Function(Input: Integer): Integer of object;
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
Button3: TButton;
procedure FormCreate(Sender: TObject);
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure Button3Click(Sender: TObject);
private
FunctionToCall: TFunction;
fValue: integer;
function ThisisFunctionA(Delta: Integer): Integer;
function ThisisFunctionB(Delta: Integer): Integer;
public
property aValue: integer read fValue write fValue;
end;
var
Form1 : TForm1;
implementation
{$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.
ASKER
Thanx all, first example is god (all are) , i only sleep a few hours so i not c...
ASKER
(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...