Example of Delphi Event Callback Management

When developing a VCL or program, you will need to use an object event to trigger many related object methods. That is, the example of 1. n.
In Java, interface-related mode programming can also be implemented in Delphi, But I have encapsulated it through a tnotifier class. When other classes are to be implemented in the future, you can directly implements tnotifier In the attribute.
unit Unit2;

interface

uses
  Classes;
type

  INotifier = interface;

  INotifier = interface(IInterface)
  ['{0DEBB550-E67D-4CB1-8B16-A7690200D4DF}']
    procedure Register(Event:TNotifyEvent);
    procedure Unregister(Event:TNotifyEvent);
    procedure DoNotify;
  end;
  
  TNotifier=class(TInterfacedPersistent,INotifier)
  private
    FOwner: TObject;
    FList: TList;
  protected
  public
    procedure Register(Event:TNotifyEvent);
    procedure Unregister(Event:TNotifyEvent);
    procedure DoNotify;
    procedure Clear;
    constructor Create(aOwner:TObject);
    destructor Destory;
  end;

implementation
uses
  SysUtils;

type
  PNotifyEvent = ^TNotifyEvent;

{ TNotifier }

procedure TNotifier.Register(Event:TNotifyEvent);
var
  p: PNotifyEvent;
begin
  New(p);
  p^ := Event;
  FList.Add(p);
end;

procedure TNotifier.Clear;
var
  I: Integer;
begin
  for I := 0 to FList.Count - 1 do    // Iterate
  begin
    Dispose(FList.Items[I]);
  end;    // for
  FList.Clear;
end;

constructor TNotifier.Create(aOwner:TObject);
begin
  FOwner := aOwner;
  FList := TList.Create;
end;

destructor TNotifier.Destory;
begin
  Clear;
  FreeAndNil(FList);
end;

procedure TNotifier.DoNotify;
var
  I: Integer;
  p:PNotifyEvent;
begin
  for I := 0 to FList.Count - 1 do    // Iterate
  begin
    p:=  FList.Items[I];
    try
      p^(FOwner);
    finally
        // free resources
    end;  // try/finally

  end;    // for
end;

procedure TNotifier.Unregister(Event:TNotifyEvent);
var
  I: Integer;
  p,p1:PNotifyEvent;
begin
  New(p1);
  try
    p1^ := Event;
    for I := FList.Count - 1 downto 0 do    // Iterate
    begin
      p:= FList.Items[I];
      if PInteger(p)^ = PInteger(p1)^ then
      begin
        Dispose(p);
        FList.Remove(p);
      end;
    end; 
  finally
      Dispose(p1);
  end;  // try/finally   // for
end;

end.

//TData class implements INotifier

unit Unit3;

interface
uses
  Unit2;
type
  TData = class(TObject,INotifier)
  private
    FNotifier: TNotifier;
    function GetNotifier: INotifier;
  public
    constructor Create;
    destructor Destroy;
    property Notifier: INotifier read GetNotifier implements INotifier;
  end;
implementation

constructor TData.Create;
begin
  inherited Create;
  FNotifier := TNotifier.Create(self);
end;

destructor TData.Destroy;
begin
  FNotifier.Free;
  inherited Destroy;
end;

function TData.GetNotifier: INotifier;
begin
  result := FNotifier;
end;

end.

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