Question

这是秒表的示例代码，我已将其作为OmniThread库的单独线程实现。

这是我的问题：表单关闭时是否必须终止并取消任务？当表单关闭时是否会自动销毁？

uses
  System.SysUtils, System.Classes,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls,

  OtlComm, OtlTask, OtlTaskControl, OtlEventMonitor;

type
  TForm1 = class(TForm)
    OTLMonitor: TOmniEventMonitor;
    btnStartClock: TButton;
    btnStopClock: TButton;
    procedure btnStartClockClick(Sender: TObject);
    procedure btnStopClockClick(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
    procedure OTLMonitorTaskMessage(const task: IOmniTaskControl; const msg: TOmniMessage);
    procedure OTLMonitorTaskTerminated(const task: IOmniTaskControl);
  private
    { Private-Deklarationen }
    FClockTask: IOmniTaskControl;
  public
    { Public-Deklarationen }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{ Place a TOmniEventMonitor component on the form,
  name it OTLMonitor,
  implement the OnTaskTerminated event-handler: OTLMonitorTaskTerminated
  and implement the OnTaskmessage event-handler: OTLMonitorTaskMessage }

var
  StopMessage: string;

procedure ShowElapsedSeconds(const ATask: IOmniTask);
var
  ElapsedSeconds: Integer;
begin
  ElapsedSeconds := 0;
  while not ATask.Terminated do
  begin
    // stop after 10 seconds:
    if ElapsedSeconds >= 10 then BREAK;

    Inc(ElapsedSeconds);
    ATask.Comm.Send(ElapsedSeconds);
    Sleep(1000);
  end;
end;

procedure TForm1.OTLMonitorTaskMessage(const task: IOmniTaskControl; const msg: TOmniMessage);
begin
  // show elapsed seconds:
  Self.Caption := IntToStr(msg.MsgID);
end;

procedure TForm1.OTLMonitorTaskTerminated(const task: IOmniTaskControl);
begin
  FClockTask := nil;
  Self.Caption := StopMessage;
end;

procedure TForm1.btnStartClockClick(Sender: TObject);
begin
  if not Assigned(FClockTask) then // prevent multiple clock-tasks
  begin
    StopMessage := 'Automatically stopped after 10 seconds';
    FClockTask := CreateTask(ShowElapsedSeconds, 'ShowElapsedSeconds').MonitorWith(OTLMonitor).Run;
  end
  else
  begin
    MessageDlg('Clock is already running!', mtInformation, [mbOK], 0);
    { Nice: The clock continues to run even while this message dialog is displayed! }
  end;
end;

procedure TForm1.btnStopClockClick(Sender: TObject);
begin
  if Assigned(FClockTask) then
  begin
    StopMessage := 'Stopped by the user';
    FClockTask.Terminate;
    FClockTask := nil;
  end
  else
    MessageDlg('Clock is not running!', mtInformation, [mbOK], 0);
end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  if Assigned(FClockTask) then
  begin
    { Do I need to terminate and nil the clock-task here?
      Or will it be destroyed autmatically when the form closes? }
  end;
end;

Answer 1

“与OmniThreadLibrary并行编程”的作者PrimožGabrijelčič写道：

“我们还应该处理用户关闭程序的可能性在后台扫描仪处于活动状态时单击“X”按钮。我们必须捕获OnFormCloseQuery事件并告诉任务终止。

procedure TfrmBackgroundFileSearchDemo.FormCloseQuery(Sender: TObject;
var CanClose: boolean);
begin
  if assigned(FScanTask) then
  begin
    FScanTask.Terminate;
    FScanTask := nil;
    CanClose := true;
  end;
end;"

本书在http://leanpub.com/omnithreadlibrary

出售

表单关闭时终止和nil OmniThread任务？

1 个答案: