Delphi: Why A class variable affects the result of the method?

delphi

Solution

The problem is that, syntactically, `class var` introduces a class field block rather than a single class field, meaning that if you use `class var`, all following field declarations in the same visibility section will be class variables too. So now, `MainNode` becomes a class variable too and that probably causes the problems you encounter. Reformatting your code shows this a little more clearly:

public
  class var 
    ID_COUNT: Integer;
    MainNode: IDomNode;
  constructor Create(... etc.

Your options are:

move `ID_COUNT` one line down:

public
  MainNode: IDomNode;
  class var ID_COUNTER: Integer;
  constructor Create(... etc.

create a special section for `MainNode`:

public
  class var ID_COUNTER: Integer;
public
  MainNode: IDomNode;
  constructor Create(... etc.

preface `MainNode` with the `var` keyword (which, likewise, introduces a block, specifically an instance field block within the current visibility section):

public
  class var 
    ID_COUNTER: Integer;
    // any other class variables
  var 
    MainNode: IDomNode;
    // any other instance variables
  constructor Create(... etc.

Problem

This is a full simplification of my code, but even so it doesn't work when class var ID_COUNTER is there, in this code I don't use the class var, but in my real code yes, but just the existence of this class variable makes the result of 's' different. This is the most weird I have ever seen. Here is a simplification, but still doesn't Works, one Unit in 75 lines. ``` unit Umain; interface uses Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls,XMLIntf,XmlDoc,IOUtils,XMLDom,System.Generics.Collections; type TStore = class public class var ID_COUNTER: Integer; MainNode: IDomNode; constructor create(node:IDomNode); function getNode():IDomNode; end; TForm1 = class(TForm) Button1: TButton; procedure Button1Click(Sender: TObject); private { Private declarations } public FMain: TStore; function Recursive(node:IDomNode):TStore; end; var Form1: TForm1; implementation {$R *.dfm} procedure TForm1.Button1Click(Sender: TObject); var Doc:IXMLDocument; content: WideString; html: IDomNode; s: String; begin Doc := TXMLDocument.Create(Application); Doc.LoadFromFile('C:\temp\example.xml'); Doc.Active := true; html := Doc.DOMDocument.getElementsByTagName('html').item[0]; FMain := Recursive(html); s := FMain.getNode().nodeName; end; function TForm1.Recursive(node: IDOMNode):TStore; var i: Integer; store: TStore; nodeName,nodeValue:String; begin store := TStore.create(node); if(not node.hasChildNodes)then Exit(store); for i := 0 to node.childNodes.length-1 do begin Recursive(node.childNodes.item[i]); end; Exit(store); end; constructor TStore.create(node: IDOMNode); begin self.MainNode := node; end; function TStore.getNode:IDomNode; begin Result := self.MainNode; end; end. ``` Some notes: example.xml is only a simple HTML document. Everything is broken when ID_COUNTER exists, if it is commented, everything is Ok. It happens here and in my real and wide Project.

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