通过泛型接口的异步事件

Question

我得把几个测量设备连到我的应用程序上。在客户端，我使用带有通用方法(QueryValue)的接口。设备在COM端口上连接，并以异步方式访问：

1. 请求一个值(=在COM端口上发送特定的字符序列)
2. 等待回应

在“业务”方面，我的组件在内部使用TComPort，数据接收事件是TComPort.OnRxChar。我想知道我怎么才能通过界面触发这个事件呢？以下是我迄今所做的工作：

IDevice = interface
  procedure QueryValue;
  function GetValue: Double;
end;

TDevice = class(TInterfacedObject, IDevice)
private
  FComPort: TComPort;
  FValue: Double;
protected
  procedure ComPortRxChar;
public
  constructor Create;
  procedure QueryValue;
  function GetValue: Double;
end;

constructor TDevice.Create;
begin
  FComPort := TComPort.Create;
  FComPort.OnRxChar := ComPortRxChar;
end;

// COM port receiving data
procedure TDevice.ComPortRxChar;
begin
  FValue := ...
end;

procedure TDevice.GetValue;
begin
  Result := FValue;
end;

但是我需要一个事件来知道什么时候在客户端调用GetValue。执行这种数据流的通常方法是什么？

Answer 1

可以将事件属性添加到接口中。

IDevice = interface
  function GetValue: Double;
  procedure SetMyEvent(const Value: TNotifyEvent);
  function GetMyEvent: TNotifyEvent;
  property MyEvent: TNotifyEvent read GetMyEvent write SetMyEvent;
end;

并在TDevice类中实现。

TDevice = class(TInterfacedObject, IDevice)
private
  FMyEvent: TNotifyEvent;
  procedure SetMyEvent(const Value: TNotifyEvent);
  function GetMyEvent: TNotifyEvent;
public
  function GetValue: Double;
  procedure EmulChar;
end;

然后，像通常一样，在FMyEvent的末尾调用ComPortRxChar处理程序(如果被分配的话)。

 Tform1...
  procedure EventHandler(Sender: TObject);

procedure TForm1.EventHandler(Sender: TObject);
var
  d: Integer;
  i: IDevice;
begin
  i := TDevice(Sender) as IDevice;
  d := Round(i.GetValue);
  ShowMessage(Format('The answer is %d...', [d]));
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  id: IDevice;
begin
  id:= TDevice.Create;
  id.MyEvent := EventHandler;
  (id as TDevice).EmulChar; //emulate rxchar arrival
end;

procedure TDevice.EmulChar;
begin
  if Assigned(FMyEvent) then
    FMyEvent(Self);
end;

function TDevice.GetMyEvent: TNotifyEvent;
begin
  Result := FMyEvent;
end;

function TDevice.GetValue: Double;
begin
  Result := 42;
end;

procedure TDevice.SetMyEvent(const Value: TNotifyEvent);
begin
  FMyEvent := Value;
end;