NodeObserverPattern.pas

unit NodeObserverPattern;

interface

uses
  classes,
  ipeernodeunit,
  System.Generics.Collections;

type
  TMSGType = (msgtrefresh, msgtserverconnected, msgtprotocolconnected);

  // Node Observer pattern
  INodeObserver = interface
    ['{C805DD3C-5A0C-4FD3-A1D5-30DF1BC53835}']
    procedure DoNotify(const msgtype: TMSGType; const aNode: INode);
  end;

  INodeObservable = interface
    ['{1ECE5AAA-F65E-4BF8-8527-75185C73A1D5}']
    procedure Notify(const msgtype: TMSGType; aNode: INode);
    procedure RegisterObserver(aObserver: INodeObserver);
    procedure UnregisterObserver(aObserver: INodeObserver);
  end;

  TNodeObservable = class(TInterfacedObject, INodeObservable)
  private
    fObserverList: Tlist<INodeObserver>;
  public
    destructor Destroy; override;
    procedure Notify(const msgtype: TMSGType; aNode: INode);
    procedure RegisterObserver(aObserver: INodeObserver);
    procedure UnregisterObserver(aObserver: INodeObserver);
  end;

procedure AttachObserverToSubject(aObserver: INodeObserver; aSubject: INodeObservable);
procedure DeattachObserverFromSubject(aObserver: INodeObserver; aSubject: INodeObservable);

implementation

procedure AttachObserverToSubject(aObserver: INodeObserver; aSubject: INodeObservable);
begin
  aSubject.RegisterObserver(aObserver);
end;

procedure DeattachObserverFromSubject(aObserver: INodeObserver; aSubject: INodeObservable);
begin
  aSubject.UnregisterObserver(aObserver);
end;

destructor TNodeObservable.Destroy;
begin
  fObserverList.free;

  inherited;
end;

procedure TNodeObservable.Notify(const msgtype: TMSGType; aNode: INode);
var
  aObserver: INodeObserver;
begin
  for aObserver in fObserverList do
  begin
    aObserver.DoNotify(msgtrefresh, aNode);
  end;
end;

procedure TNodeObservable.RegisterObserver(aObserver: INodeObserver);
begin
  if fObserverList = nil then
    fObserverList := Tlist<INodeObserver>.Create;

  if fObserverList.IndexOf(aObserver) < 0 then
    fObserverList.Add(aObserver);
end;

procedure TNodeObservable.UnregisterObserver(aObserver: INodeObserver);
begin
  if fObserverList <> nil then
    fObserverList.Remove(aObserver);
end;

end.