delphi - 在运行时创建并运行 TTimer

Question

我试图在 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，我在运行时创建了一个 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，编译器返回以下错误:

[DCC Error] unit1.pas(2153): E2010 Incompatible types: 'TNotifyEvent' and 'procedure, untyped pointer or untyped parameter'"

有什么提示吗？

Answer 1

TNotifyEvent 声明为:

TNotifyEvent = procedure(Sender: TObject) of object;

of object 使它成为一个closure，这是一种特殊类型的方法指针，带有2个指针——一个指向对象的指针，一个指向非对象的指针- 在对象上调用的静态类方法。因此，您不能将独立函数(当然也不能是嵌套函数)直接分配给 TNotifyEvent。这就是编译器所提示的。

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，这样您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 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，是一种无需使用任何类包装器即可使用独立函数的方法:

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;