TJclStringList 在免费时崩溃

Question

创建一个简单的 VCL 应用程序：

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs;

type
  TForm1 = class(TForm)
   procedure FormDestroy(Sender: TObject);
   procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses
  JclStringLists;

var
  MyList1: TJclStringList;
  MyList2: TJclStringList;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  MyList1.Free;
  MyList2.Free;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  MyList1 := TJclStringList.Create;
  MyList2 := TJclStringList.Create;
  MyList1.LoadFromFile('C:\ONE.txt');
  MyList2.LoadFromFile('C:\TWO.txt');
  Self.Caption := Self.Caption + ' ' + IntToStr(MyList1.Count);
  Self.Caption := Self.Caption + ' ' + IntToStr(MyList2.Count);
end;

end.

尝试释放 MyList1 对象实例时，它在 TForm1.FormDestroy 事件处理程序中崩溃。为什么？

Answer 1

TJclStringList 是引用计数类型（它在 JCLStringLists.pas 中声明为 type TJclStringList = class(TJclInterfacedStringList, IInterface, IJclStringList) 并同时实现 _AddRef 和 _Release 来处理引用计数），所以你根本不应该将它们创建为对象，也不应该手动释放它们——当对它们的引用超出范围时，它们将自动释放。（这也意味着你不应该将它们声明为全局变量，因为这样你就无法控制它们的生命周期。）

JclStringLists 单元提供了几个函数，可以正确地为您创建接口实例。您可以在该单元中看到它们，就在 implementation 关键字上方：

function JclStringList: IJclStringList; overload;
function JclStringListStrings(AStrings: TStrings): IJclStringList; overload;
function JclStringListStrings(const A: array of string): IJclStringList; overload;
function JclStringList(const A: array of const): IJclStringList; overload;
function JclStringList(const AText: string): IJclStringList; overload;

使用 TJclStringList 做你想做的事情的正确方法是这样的：

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, JCLStringLists;

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
    MyList1, MyList2: IJCLStringList;  // Note I and not T in type.
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  MyList1 := JclStringList;
  MyList1.LoadFromFile('C:\Work\Data\FirstName.txt');
  MyList2 := JclStringList
  MyList2.LoadFromFile('C:\Work\Data\LastName.txt');

  // Only to demonstrate that both files got loaded by the code above.
  Self.Caption := Format('First: %d Last: %d', [MyList1.Count, MyList2.Count]);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  // Do NOT free the JclStringLists here - they will automatically be released when
  // the form is destroyed because the reference count will reach zero (as long as
  // you don't have any other references to those variables, which by putting them into
  // the private section is unlikely.
end;

end.

TJclStringList 在免费时崩溃

TJclStringList crashes on Free

delphi

jedi

delphi-10.1-berlin