Delphi - 在运行时创建的 TXMLDocument 生成 AV，表单上的组件正在运行

Question

我正在运行时创建 TXMLDocument 的实例，以加载和解析 XML 文件。您可以检查以下代码:

    unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, xmldom, XMLIntf, msxmldom, XMLDoc, StdCtrls;

type
  Txml = class(TForm)
//    XMLDocument1: TXMLDocument;
    Memo1: TMemo;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  xml: Txml;

implementation

{$R *.dfm}

procedure Txml.FormCreate(Sender: TObject);
var    i,j:integer;
       aNode:IXMLNode;
       ws:String;
       XMLDocument1:TXMLDocument;
begin
 Memo1.Lines.Clear;
 XMLDocument1 := TXMLDocument.Create(nil);
 try
  XMLDocument1.LoadFromFile('C:\a.xml');
  XMLDocument1.Active := true;
  aNode := XMLDocument1.ChildNodes.First;
  while aNode<>nil do
  begin
   for i := 0 to aNode.ChildNodes.Count-1 do
    begin
     if aNode.ChildNodes[i].NodeName = 'Role' then
      begin
       Memo1.Lines.Add('Tag - '+aNode.ChildNodes[i].ChildNodes['Tag'].Text);
       for j := 0 to aNode.ChildNodes[i].ChildNodes.Count-1 do
        if aNode.ChildNodes[i].ChildNodes[j].HasChildNodes then
         begin
          ws :=  VarToStr(aNode.ChildNodes[i].ChildNodes[j].ChildValues['Tag']);
          if trim(ws)<>'' then
           Memo1.Lines.Add(ws);
          ws :=  VarToStr(aNode.ChildNodes[i].ChildNodes[j].ChildValues['Value']);
          if trim(ws)<>'' then
           Memo1.Lines.Add(ws);
         end;
      end;
    end;
   aNode := aNode.NextSibling;
  end;
  XMLDocument1.Active := false;
 finally
   FreeAndNil(XMLDocument1);
 end;
end;

end.

问题是这正在生成 AV。正如您可能已经看到的，在组件出现在表单上之前 (//XMLDocument1: TXMLDocument;)。

为什么当组件位于表单上时代码可以工作，但是当我在运行时创建它时它会生成 AV？

LE:解决方案:基于答案/评论和Delphi帮助:

XMLDocument1 : IXMLDocument;  //not TXMLDocument

XMLDocument1 := LoadXMLDocument(...);

FreeAndNil;// must be deleted

Answer 1

据我所知，您应该改用接口(interface)IDoc: IXMLDocument;。

来自文档:

When TXMLDocument is created without an Owner, it behaves like an interfaced object. That is, when all references to its interface are released, the TXMLDocument instance is automatically freed. When TXMLDocument is created with an Owner, however, it behaves like any other component, and is freed by its Owner.

换句话说，当创建具有 nil 所有者的 TXMLDocument 实例时，不要调用 Free() 或实例上的 FreeAndNil()，并且您必须将对象分配给 IXMLDocument 变量，以便正确管理其当前事件的引用计数.