Save/Load TObject(TPersistent) to XML

Question

everybody.

I'm trying to save my class:

TA= class(TPersistent)
private
    FItems: TObjectList<TB>;

    FOnChanged: TNotifyEvent;
public
    constructor Create;
    destructor Destroy; override;
    ...
    procedure Delete(Index: Integer);
    procedure Clear;
    procedure SaveToFile(const FileName: string);
    ...
    property OnChanged: TNotifyEvent read FOnChanged write FOnChanged;
end;

to file using the following code:

var
  Storage: TJvAppXMLFileStorage;
begin
  Storage := TJvAppXMLFileStorage.Create(nil);
  try
    Storage.WritePersistent('', Self);
    Storage.Xml.SaveToFile(FileName);
  finally
    Storage.Free;
  end;

but file is always empty.

What am I doing the wrong way?

Answer 1

It looks like TJvCustomAppStorage does not support Generics in properties. The code makes no use of extended RTTI and the call to TJvCustomAppStorage.GetPropCount returns 0.

This leads to another question - Are there Delphi object serialization libraries with support for Generics??

My test code:

program Project1;

{$APPTYPE CONSOLE}

uses
  SysUtils, Classes, Generics.Collections, JvAppXmlStorage;
type

  TA = class(TPersistent)
  private
    FItems: TObjectList<TPersistent>;
  public
    constructor Create;
  published
    property
      Items: TObjectList < TPersistent > read FItems write FItems;
  end;

  { TA }

constructor TA.Create;
begin
  FItems := TObjectList<TPersistent>.Create;
end;

var
  Storage: TJvAppXMLFileStorage;
  Test: TA;
begin
  Test := TA.Create;

  Test.Items.Add(TPersistent.Create);

  Storage := TJvAppXMLFileStorage.Create(nil);
  try
    Storage.WritePersistent('', Test);
    WriteLn(Storage.Xml.SaveToString);
    ReadLn;
  finally
    Storage.Free;
  end;

end.

Answer 2

I'm not sure but if TJvAppXMLFileStorage uses RTTI then I think you have to publish the properties that you want to save / load.