Rafael: /* NG SerializerPack */

2015-05-27T16:02:09Z

‎NG SerializerPack

Rafael at 16:01, 27 May 2015

2015-05-27T16:01:40Z

Rafael: Created page with "{{Head-Overview}} Category:FAQ"

2015-05-27T16:00:45Z

Created page with "{{Head-Overview}} Category:FAQ"

New page

{{Head-Overview}} [[Category:FAQ]]

@@ Line 94: / Line 94: @@
 </pre>
-As can be seen, TItems collection is oqned by TOwner class. TOwner expose Items as read-only property, and thus, there no way to replace collection as a whole. Only collection content can be changed.
+As can be seen, TItems collection is owned by TOwner class. TOwner expose Items as read-only property, and thus, there no way to replace collection as a whole. Only collection content can be changed.
 But, fortunately, TOwner class can be serialized and de-serialized, because TItems collection has fill-read mode converter:

← Older revision		Revision as of 16:01, 27 May 2015
Line 1:		Line 1:
	{{Head-Overview}} [[Category:FAQ]]		{{Head-Overview}} [[Category:FAQ]]
		+
		+	==NG SerializerPack==
		+	===How to serialize collections===
		+	Serializing collections, including custom or standard collections (like TList) requires writing custom converters. For example, lets consider the folowing collection declaration:
		+
		+	<pre class="brush:delphi">
		+	type
		+	TItem = class
		+	public
		+	X: Integer;
		+	Y: Integer;
		+	end;
		+
		+	TItems = class(TObjectList<TItem>);
		+	</pre>
		+
		+	To be able to serialize it, we need to declare a converter class, and '''associate''' this class with our collection using Converter attribute:
		+
		+	<pre class="brush:delphi">
		+	type
		+	TItemsConverter = class(TConverter)
		+	public
		+	function GetReadMode: TReadMode; override;
		+	procedure Write(S: TSerializer; const V); override;
		+	procedure Read(D: TDeserializer; var V); override;
		+	end;
		+
		+	[Converter(TItemsConverter)]
		+	TItems = class(TObjectList<TItem>);
		+	</pre>
		+
		+	The converter can be implemented like this:
		+
		+	<pre class="brush:delphi">
		+	function TItemsConverter.GetReadMode: TReadMode;
		+	begin
		+	Result := rmFillRead; // Indicate fill-read mode.
		+	end;
		+
		+	procedure TItemsConverter.Read(D: TDeserializer; var V);
		+	var
		+	lst: TItems;
		+	begin
		+	lst := TItems(V); // Since we work in fill-read mode,
		+	// V already contains a reference to
		+	// TItems instance; we should not
		+	// create it here.
		+	lst.Clear;
		+
		+	D.BeginArray;
		+	while D.HasNext do
		+	lst.Add(D.Value<TItem>);
		+	D.EndArray;
		+	end;
		+
		+	procedure TItemsConverter.Write(S: TSerializer; const V);
		+	var
		+	lst: TItems;
		+	i: Integer;
		+	begin
		+	S.BeginArray;
		+	lst := TItems(V);
		+	for i := 0 to lst.Count - 1 do
		+	S.Value(lst[i]);
		+	S.EndArray;
		+	end;
		+	</pre>
		+
		+	As can be seen, GetReadMode returns rmFillRead, which indicates that de-serializer should use fill-read mode. This means that no new TItems instance is created during de-serialization. This mode is especially usefull for collection like classes, because they usually owned by some other objects. For example, lets look at the following class:
		+
		+	<pre class="brush:delphi">
		+	type
		+	TOwner = class
		+	private
		+	FItems: TItems;
		+	public
		+	constructor Create;
		+	destructor Destroy; override;
		+	property Items: TItems read FItems;
		+	end;
		+
		+	constructor TOwner.Create;
		+	begin
		+	inherited Create;
		+	FItems := TItems.Create;
		+	end;
		+
		+	destructor TOwner.Destroy;
		+	begin
		+	FItems.Free;
		+	inherited;
		+	end;
		+	</pre>
		+
		+	As can be seen, TItems collection is oqned by TOwner class. TOwner expose Items as read-only property, and thus, there no way to replace collection as a whole. Only collection content can be changed.
		+
		+	But, fortunately, TOwner class can be serialized and de-serialized, because TItems collection has fill-read mode converter:
		+
		+	<pre class="brush:delphi">
		+	var
		+	src, dst: TOwner;
		+	stream: TStream;
		+	s: TBinarySerializer;
		+	d: TBinaryDeserializer;
		+	begin
		+	stream := TMemoryStream.Create;
		+	try
		+	src := TOwner.Create;
		+	src.Items.Add(TItem.Create);
		+	src.Items.Add(TItem.Create);
		+	src.Items.Add(TItem.Create);
		+
		+	s := TBinarySerializer.Create(stream);
		+	s.Value(src);
		+	s.Free;
		+
		+	stream.Position := 0;
		+
		+	d := TBinaryDeserializer.Create(stream);
		+	dst := d.Value<TOwner>;
		+	d.Free;
		+	finally
		+	stream.Free;
		+	end;
		+	end;
		+	</pre>
		+
		+	Please use the following link for more information about fill-read mode:
		+	[http://www.lmd.de/downloads/tutorials/serialization/index.html?fill-read_mode.htm Fill-Read Mode]

LMD NG-Packs - Revision history

Rafael: /* NG SerializerPack */

Rafael at 16:01, 27 May 2015

Rafael: Created page with "{{Head-Overview}} Category:FAQ"