multithreading - Delphi - 未创建自定义线程

Question

我这里有点问题。我有一个继承 TPersistent 类的自定义类，在这个自定义类内部(私有(private)部分)，我有一个自定义的 TThread，它具有覆盖的 Execute 方法，每(1000 毫秒)触发一次。一切都很好，直到我将我的 2 个自定义类移动到一个新单元......

type
  TMyThread= class(TThread)
  protected
   procedure Execute; override;
  end;

  TMyClass = class(TPersistent)
  private
   T: TMyThread;
  protected
   constructor Create;
  public
   destructor Destroy; override;
  end;


implementation

procedure TMyThread.Execute;
begin
 while not Self.Terminated do begin
  Sleep(1000);
  MessageBox(0, 'test', nil, MB_OK)
 end;
end;

constructor TMyClass.Create;
begin
 inherited Create;
 t := TMyThread.Create(False);
end;

destructor TMyClass.Destroy;
begin
 t.Terminate;
 t.WaitFor;
 FreeAndNil(t);
 inherited Destroy;
end;

上面的代码在主项目单元中工作得很好，但是当我将它移动到一个新单元时，线程代码不再工作，当我尝试释放一个 TMyClass 对象时，我得到一个 AV。我认为线程根本没有被构建，这就是为什么我在尝试释放它时得到一个 AV ......但为什么呢？代码在哪个单元中并不重要...

单元1:

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, unit2;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    procedure Button2Click(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  p: TMyClass;

implementation

{$R *.dfm}

procedure TForm1.Button2Click(Sender: TObject);
begin
 p.Free; //Getting an AV
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
 p := TMyClass.Create;
end;

end.

单元2:

unit Unit2;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;

type
  TMyThread = class(TThread)
  protected
   procedure Execute; override;
  end;

  TMyClass = class(TPersistent)
  private
   T: TMyThread;
  protected
   constructor Create;
  public
   destructor Destroy; override;
  end;


implementation

procedure TMyThread.Execute;
begin
 while not Self.Terminated do begin
  Sleep(1000);
  MessageBox(0, 'test', nil, MB_OK)
 end;
end;

constructor TMyClass.Create;
begin
 inherited Create;
 t := TMyThread.Create(False);
end;

destructor TMyClass.Destroy;
begin
 t.Terminate;
 t.WaitFor;
 FreeAndNil(t);
 inherited Destroy;
end;

end.

Answer 1

构造函数TMyClass.Create被宣布为 protected 。这意味着从另一个单元看不到它。因此TMyClass.Create未执行，而是调用 TObject.Create .反过来，这意味着线程永远不会被创建，并且在析构函数运行时会遇到运行时错误，因为 T是 nil .

用 public 声明构造函数能见度。