Saving a TObject to a File

Question

How can one save an Object, in its current state, to a file? So that it can immediately be read and restored with all its variables.

Answer 1

There is a good tutorial here. Keep in mind that you have to have RTTI (run time type information) to save an object at run-time using this approach, so it will only capture published properties of a class.

Answer 2

If you descend your object from TComponent, you can use some built-in functionality to stream the object to a file. I think this only works well for simple objects.

Some sample code to get you started:

unit Unit1;

interface

uses
  Classes;

type
  TMyClass = class(TComponent)
  private
    FMyInteger: integer;
    FMyBool: boolean;
    FMyString: string;
  public
    procedure ToFile(AFileName: string);
  published
    property MyInteger: integer read FMyInteger write FMyInteger;
    property MyString: string read FMyString write FMyString;
    property MyBool: boolean read FMyBool write FMyBool;
  end;

implementation

{ TMyClass }

procedure TMyClass.ToFile(AFileName: string);
var
  MyStream: TFileStream;
begin
  MyStream := TFileStream.Create(AFileName);
  try
    Mystream.WriteComponent(Self);
  finally
    MyStream.Free;
  end;
end;

end.

Answer 3

There's also a roll-your-own XML method here on S.O.

Answer 4

1. Very simple and efficient solution: DragonSoft's XML Class Serializer

2. Also you can use JVCL TJvAppXMLFileStorage:

   uses JvAppXMLStorage;

   var
     Storage: TJvAppXMLFileStorage;
   begin
     Storage := TJvAppXMLFileStorage.Create(nil);
     try
       Storage.WritePersistent('', MyObject);
       Storage.Xml.SaveToFile('S:\TestFiles\Test.xml');
       Storage.Xml.LoadFromFile('S:\TestFiles\Test.xml');
       Storage.ReadPersistent('', MyObject);
     finally
       Storage.Free;
     end;
   end;
   

Answer 5

As already stated, the easiest way is to use a Stream and its WriteComponent and ReadComponent methods.
But be aware that :
- it works for descendants of TComponent, not plain TObject;
- only for the published properties (those saved in a dfm), not the public ones nor (a fortiori) the privwte ones;
- you have to pay a special attention for the Name property when restoring the component.

You may find some code you could use in these SO answers: Replace visual component at runtime in Delphi, Duplicating components at Run-Time

Answer 6

You've already gotten some good answers to your question. Depending on what you're actually doing, it might be desirable to use a pre-built library or component to save objects. This is an inexpensive and nifty library/component set that makes it trivial to persist and restore objects, and pretty easily (i.e., with a little bit of code) accommodates persisting even unpublished members of an object: http://www.deepsoftware.ru/rsllib/index.html Not something that's rocket science, but if you're doing a lot of this sort of thing this component provides a nice framework for it.

Developer Express also includes a general purpose cxPropertiesStore component as part of the ExpressEditors library that comes with some of their components.