在运行时创建和运行TTimer

Question

我正试图在Delphi中实现类似于Javascript的setTimeout()过程的行为:在延迟几秒钟后运行。为此，我在运行时创建一个TTimer，运行它，然后释放它。

这是我的代码：

procedure createAndRunTimer();
  procedure goTimer(Sender: TObject);
  begin
    (sender as ttimer).enabled := false;
    // do stuff here
    sender.free;
  end;
var
  t : TTimer;
begin
  t := TTimer.Create(frmprinc);
  t.Interval := 5000;
  t.OnTimer := goTimer(t);
end;

但是我的代码无法编译，编译器将返回以下错误：

DCC错误单元1.PAS(2153)：E2010不兼容类型：“TNotifyEvent”和“过程、非类型化指针或非类型化参数”

有什么暗示吗？

Answer 1

TNotifyEvent声明为：

TNotifyEvent = procedure(Sender: TObject) of object;

of object使其成为一个闭包，它是一种特殊类型的方法指针，包含两个指针--一个指向对象的指针，以及一个指向在对象上调用的非静态类方法的指针。因此，不能直接将独立函数(当然不是嵌套函数)分配给TNotifyEvent。这正是编译器所抱怨的。

因此，您需要声明一个类来包装OnTimer事件处理程序，例如：

type
  TTimerEvents = class
  public
    procedure goTimer(Sender: TObject);
  end;

procedure TTimerEvents.goTimer(Sender: TObject);
begin
  (Sender as TTimer).Enabled := false;

  // do stuff here

  // NOTE: you cannot destroy the Sender object from here, you must delay
  // the destruction until after this handler exits!  You can post a
  // custom window message via PostMessage() and have the message handler
  // call Sender.Free().  Or, you can use a worker thread to call
  // Sender.Free() via TThread.Synchronize() (or TThread.Queue() in Delphi
  // 8 and later).  Or, in Delphi 10.2 Tokyo and later, you can call
  // Sender.Free() via TThread.ForceQueue().  Or, use whatever other
  // mechanism you want to use to call Sender.Free(), as long as it works
  // asynchronously and calls Sender.Free() in the same thread that
  // constructed the TTimer object ...
end;

var
  events: TTimerEvents;

procedure createAndRunTimer();
var
  t : TTimer;
begin
  t := TTimer.Create(frmprinc);
  t.Interval := 5000;
  t.OnTimer := events.goTimer;
  t.Enabled := True;
end;

initialization
  events := TTimerEvents.Create;
finalization
  events.Free;

或者，您可以使用class方法，这样就不需要包装类的实际实例：

type
  TTimerEvents = class
  public
    class procedure goTimer(Sender: TObject);
  end;

class procedure TTimerEvents.goTimer(Sender: TObject);
begin
  (Sender as TTimer).Enabled := false;

  // do stuff here

  // delay-destroy the Sender as needed ...
end;

procedure createAndRunTimer();
var
  t : TTimer;
begin
  t := TTimer.Create(frmprinc);
  t.Interval := 5000;
  t.OnTimer := TTimerEvents.goTimer;
  t.Enabled := True;
end;

或者，在Delphi 2006及更高版本中，您可以使用类帮助者

type
  TTimerHelper = class helper for TTimer
  public
    procedure goTimer(Sender: TObject);
  end;

procedure TTimerHelper.goTimer(Sender: TObject);
begin
  (Sender as TTimer).Enabled := false;

  // do stuff here

  // delay-destroy the Sender as needed ...
end;

procedure createAndRunTimer();
var
  t : TTimer;
begin
  t := TTimer.Create(frmprinc);
  t.Interval := 5000;
  t.OnTimer := t.goTimer;
  t.Enabled := True;
end;

尽管如此，还是有一种方法可以使用独立函数，而无需使用任何类包装器：

procedure goTimer(Self: Pointer; Sender: TObject);
begin
  (Sender as TTimer).Enabled := false;

  // do stuff here

  // delay-destroy the Sender as needed ...
end;

procedure createAndRunTimer();
var
  t : TTimer;
  event : TNotifyEvent;
begin
  t := TTimer.Create(frmprinc);
  t.Interval := 5000;

  TMethod(event).Data := nil; // or whatever you want to pass to the Self parameter...
  TMethod(event).Code := @goTimer;
  t.OnTimer := event;

  t.Enabled := True;
end;

Answer 2

我使用Torry的这个过程作为延迟，它不会在执行时锁定线程：

procedure Delay(dwMilliseconds: Longint);
var
  iStart, iStop: DWORD;
begin
  iStart := GetTickCount;
  repeat
    iStop := GetTickCount;
    Application.ProcessMessages;
    Sleep(1);
  until (iStop - iStart) >= dwMilliseconds;
end;