Mega Code Archive
How to store events in a TList
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Title: How to store events in a TList?
Question: How do you store events in a list? Let's say a TTimer descendant has to process a number of events of other components.
Answer:
Since TNotifyEvents are methods of objects, you need to store the objects in
the list so the hidden "self" parameter can also be stored in the list.
Example:
object Form1: TForm1
Left = 362
Top = 161
Width = 364
Height = 184
Caption = 'Form1'
Color = clBtnFace
Font.Charset = DEFAULT_CHARSET
Font.Color = clWindowText
Font.Height = -11
Font.Name = 'MS Sans Serif'
Font.Style = []
OldCreateOrder = False
OnCreate = FormCreate
OnDestroy = FormDestroy
PixelsPerInch = 96
TextHeight = 13
object Button1: TButton
Left = 40
Top = 16
Width = 75
Height = 25
Caption = 'Button1'
TabOrder = 0
OnClick = Button1Click
end
object Button2: TButton
Left = 40
Top = 64
Width = 75
Height = 25
Caption = 'Button2'
TabOrder = 1
OnClick = Button2Click
end
object Button3: TButton
Left = 40
Top = 104
Width = 75
Height = 25
Caption = 'Button3'
TabOrder = 2
OnClick = Button3Click
end
object Edit1: TEdit
Left = 152
Top = 16
Width = 121
Height = 21
TabOrder = 3
Text = 'Edit1'
end
object Edit2: TEdit
Left = 152
Top = 64
Width = 121
Height = 21
TabOrder = 4
Text = 'Edit2'
end
object Edit3: TEdit
Left = 152
Top = 104
Width = 121
Height = 21
TabOrder = 5
Text = 'Edit3'
end
object Timer1: TTimer
OnTimer = Timer1Timer
Left = 296
Top = 48
end
end
unit timeru;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics,
Controls, Forms, Dialogs, ExtCtrls, StdCtrls;
type
TMethodContainer = class
TheMethod: TNotifyEvent;
end;
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
Button3: TButton;
Edit1: TEdit;
Edit2: TEdit;
Edit3: TEdit;
Timer1: TTimer;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure Button3Click(Sender: TObject);
procedure Timer1Timer(Sender: TObject);
private
{ Private declarations }
x, y, z: integer;
FOnTimerList: TList;
procedure UpdateEdits(Sender: TObject);
procedure SetOnTimer(Value: TNotifyEvent);
procedure ClearTimer(Value: TNotifyEvent);
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.Button1Click(Sender: TObject);
begin
inc(x);
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
inc(y);
end;
procedure TForm1.Button3Click(Sender: TObject);
begin
inc(z);
end;
procedure TForm1.UpdateEdits(Sender: TObject);
begin
edit1.text := 'X = ' + inttostr(x);
edit2.text := 'Y = ' + inttostr(y);
edit3.text := 'Z = ' + inttostr(z);
end;
procedure TForm1.Timer1Timer(Sender: TObject);
var
i: integer;
begin
for i := 0 to FOnTimerList.Count - 1 do
with TMethodContainer(FOnTimerList.Items[i]) do
if assigned(TheMethod) then
TheMethod(Self);
end;
procedure TForm1.SetOnTimer(Value: TNotifyEvent);
var
TM: TMethodContainer;
begin
if Assigned(Value) then
begin
Timer1.enabled := false;
TM := TMethodContainer.create;
TM.TheMethod := value;
FOnTimerList.Add(pointer(TM));
Timer1.enabled := true;
end;
end;
procedure TForm1.ClearTimer(Value: TNotifyEvent);
var
i: integer;
found: boolean;
function IsEqual(var p1, p2): boolean;
begin
result := pointer(p1) pointer(p2);
end;
begin
if Assigned(Value) then
begin
Timer1.enabled := false;
i := 0;
found := false;
while (i begin
with TMethodContainer(FOnTimerList.Items[i]) do
found := IsEqual(TheMethod, Value);
if not (found) then
inc(i);
end;
if found then
begin
TMethodContainer(FOnTimerList.Items[i]).Free;
FOnTimerList.delete(i);
end;
Timer1.enabled := true;
end;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
FOnTimerList := TList.create;
SetOnTimer(Button1Click);
SetOnTimer(Button2Click);
SetOnTimer(Button3Click);
SetOnTimer(UpdateEdits);
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
ClearTimer(UpdateEdits);
ClearTimer(Button3Click);
ClearTimer(Button2Click);
ClearTimer(Button1Click);
FOnTimerList.free;
end;
end.
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