Question

我试图在Delphi中实现类似于Javascript setTimeout过程的行为：在延迟几秒后运行。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;

但我的代码无法编译，IDE会返回以下错误：

[DCC错误] unit1.pas（2153）：E2010不兼容的类型：'TNotifyEvent' 和'过程，无类型指针或无类型参数'“

任何提示？

由于

Answer 1

TNotifyEvent声明为：

TNotifyEvent = procedure(Sender: TObject) of object;

of object使它成为闭包，这是一种特殊类型的方法指针，带有2个指针 - 指向对象的指针，以及指向非静态类方法的指针在对象上调用它。因此，您不能将独立函数（当然也不是嵌套函数）直接分配给TNotifyEvent。这就是编译器所抱怨的。

因此，您需要声明一个类来包装您的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，因此您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class helper：

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;

话虽如此， IS 是一种使用独立函数而不使用任何类包装器的方法：

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的这个程序作为延迟，它在执行时不会锁定线程：

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

在运行时创建并运行TTimer

2 个答案: