示例:推模型(push model)
說明:
目標向觀察者發送關於改變的詳細信息,而不管它們需要與否。
代碼:
unit uPushModel;
interface
uses
SysUtils, Classes, Dialogs;
type
TSubjectState = record
A,B:Integer;
end;
TObserver = class;
TSubject = class
private
FObservers: TList;
FState: TSubjectState;
public
constructor Create;
destructor Destroy; override;
//---
procedure Attach(AObserver: TObserver);
procedure Detach(AObserver: TObserver);
procedure Notify;
end;
TConcreteSubject = class(TSubject)
private
function GetA: Integer;
function GetB: Integer;
procedure SetA(const Value: Integer);
procedure SetB(const Value: Integer);
public
property A: Integer read GetA write SetA;
property B: Integer read GetB write SetB;
end;
TObserver = class
public
procedure Update(AState: TSubjectState); virtual; abstract;
end;
TConcreteObserver = class(TObserver)
protected
FSubject: TSubject;
public
constructor Create(ASubject: TSubject);
destructor Destroy; override;
//---
procedure Update(AState: TSubjectState); override;
end;
procedure Test;
implementation
procedure Test;
var
ASubject: TConcreteSubject;
AObserver: TObserver;
begin
ASubject := TConcreteSubject.Create;
AObserver := TConcreteObserver.Create(ASubject);
try
ASubject.A := 1;
ASubject.B := 2;
ASubject.Notify;
finally
AObserver.Free;
ASubject.Free;
end;
end;
constructor TSubject.Create;
begin
FObservers := TList.Create;
end;
destructor TSubject.Destroy;
begin
FObservers.Free;
//---
inherited;
end;
procedure TSubject.Attach(AObserver: TObserver);
begin
FObservers.Add(AObserver);
end;
procedure TSubject.Detach(AObserver: TObserver);
begin
FObservers.Remove(AObserver);
end;
procedure TSubject.Notify;
var
i: integer;
begin
with FObservers do
begin
for i := 0 to Count - 1 do
TObserver(Items[i]).Update(FState);
end;
end;
constructor TConcreteObserver.Create(ASubject: TSubject);
begin
FSubject := ASubject;
if FSubject <> nil then FSubject.Attach(self);
end;
destructor TConcreteObserver.Destroy;
begin
if FSubject <> nil then FSubject.Detach(self);
//---
inherited;
end;
procedure TConcreteObserver.Update(AState: TSubjectState);
begin
ShowMessage(IntToStr(AState.A + AState.B))
end;
function TConcreteSubject.GetA: Integer;
begin
Result := FState.A;
end;
function TConcreteSubject.GetB: Integer;
begin
Result := FState.B;
end;
procedure TConcreteSubject.SetA(const Value: Integer);
begin
FState.A := Value;
end;
procedure TConcreteSubject.SetB(const Value: Integer);
begin
FState.B := Value;
end;
end.
《GOF設計模式》—觀察者(OBSERVER)—Delphi源碼示例:推模型(push model)
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