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（在JCLStringLists.pas中声明为type TJclStringList = class(TJclInterfacedStringList, IInterface, IJclStringList)，并且同时实现_AddRef和_Release来处理引用计数），因此您完全不应该将它们创建为对象，并且您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。（这也意味着您不应该将它们声明为全局变量，因为那样您就无法对其生命周期保持控制。）

JclStringLists单元提供了几种功能，可以为您正确创建接口的实例。您可以在implementation关键字上方的那个单元中看到它们：

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进行所需操作的正确方法是：

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免费崩溃

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