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Как сохранить значение свойства в поток 2



Автор: Yoav

The solution above will work, but it forces you to implement streaming support for each of the TStreamableObject objects. Delphi has already implemented this mechanism in for the TPersistent class and the TComponent class, and you can use this mechanism. The class I include here does the job. It holds classes that inherit from TUmbCollectionItem (which in turn inherits from Delphi TCollectionItem), and handles all the streaming of the items. As the items are written with the Delphi mechanism, all published data is streamed.

Notes: This class does not support working within the delphi IDE like TCollection. All objects inheriting from TUmbCollectionItem must be registered using the Classes.RegisterClass function. All objects inheriting from TUmbCollectionItem must implement the assign function. By default, the TUmbCollection owns its items (frees them when the collection is freed), but this functionality can be changed.

unit UmbCollection;

interface

uses
  Windows, Messages, SysUtils, Classes, contnrs;

type
  TUmbCollectionItemClass = class of TUmbCollectionItem;
  TUmbCollectionItem = class(TCollectionItem)
  private
    FPosition: Integer;
  public
    {when overriding this method, you must call the inherited assign.}
    procedure Assign(Source: TPersistent); override;
  published
    {the position property is used by the streaming mechanism to place the object in the
    right position when reading the items. do not use this property.}
    property Position: Integer read FPosition write FPosition;
  end;

  TUmbCollection = class(TObjectList)
  private
    procedure SetItems(Index: Integer; Value: TUmbCollectionItem);
    function GetItems(Index: Integer): TUmbCollectionItem;
  public
    function Add(AObject: TUmbCollectionItem): Integer;
    function Remove(AObject: TUmbCollectionItem): Integer;
    function IndexOf(AObject: TUmbCollectionItem): Integer;
    function FindInstanceOf(AClass: TUmbCollectionItemClass; AExact: Boolean =
      True;
      AStartAt: Integer = 0): Integer;
    procedure Insert(Index: Integer; AObject: TUmbCollectionItem);

    procedure WriteToStream(AStream: TStream); virtual;
    procedure ReadFromStream(AStream: TStream); virtual;

    property Items[Index: Integer]: TUmbCollectionItem read GetItems write
      SetItems; default;
  published
    property OwnsObjects;
  end;

implementation

{ TUmbCollection }

function ItemsCompare(Item1, Item2: Pointer): Integer;
begin
  Result := TUmbCollectionItem(Item1).Position -
    TUmbCollectionItem(Item2).Position;
end;

function TUmbCollection.Add(AObject: TUmbCollectionItem): Integer;
begin
  Result := inherited Add(AObject);
end;

function TUmbCollection.FindInstanceOf(AClass: TUmbCollectionItemClass;
  AExact: Boolean; AStartAt: Integer): Integer;
begin
  Result := inherited FindInstanceOf(AClass, AExact, AStartAt);
end;

function TUmbCollection.GetItems(Index: Integer): TUmbCollectionItem;
begin
  Result := inherited Items[Index] as TUmbCollectionItem;
end;

function TUmbCollection.IndexOf(AObject: TUmbCollectionItem): Integer;
begin
  Result := inherited IndexOf(AObject);
end;

procedure TUmbCollection.Insert(Index: Integer; AObject: TUmbCollectionItem);
begin
  inherited Insert(Index, AObject);
end;

procedure TUmbCollection.ReadFromStream(AStream: TStream);
var
  Reader: TReader;
  Collection: TCollection;
  ItemClassName: string;
  ItemClass: TUmbCollectionItemClass;
  Item: TUmbCollectionItem;
  i: Integer;
begin
  Clear;
  Reader := TReader.Create(AStream, 1024);
  try
    Reader.ReadListBegin;
    while not Reader.EndOfList do
    begin
      ItemClassName := Reader.ReadString;
      ItemClass := TUmbCollectionItemClass(FindClass(ItemClassName));
      Collection := TCollection.Create(ItemClass);
      try
        Reader.ReadValue;
        Reader.ReadCollection(Collection);
        for i := 0 to Collection.Count - 1 do
        begin
          item := ItemClass.Create(nil);
          item.Assign(Collection.Items[i]);
          Add(Item);
        end;
      finally
        Collection.Free;
      end;
    end;
    Sort(ItemsCompare);
    Reader.ReadListEnd;
  finally
    Reader.Free;
  end;
end;

function TUmbCollection.Remove(AObject: TUmbCollectionItem): Integer;
begin
  Result := inherited Remove(AObject);
end;

procedure TUmbCollection.SetItems(Index: Integer; Value: TUmbCollectionItem);
begin
  inherited Items[Index] := Value;
end;

procedure TUmbCollection.WriteToStream(AStream: TStream);
var
  Writer: TWriter;
  CollectionList: TObjectList;
  Collection: TCollection;
  ItemClass: TUmbCollectionItemClass;
  ObjectWritten: array of Boolean;
  i, j: Integer;
begin
  Writer := TWriter.Create(AStream, 1024);
  CollectionList := TObjectList.Create(True);
  try
    Writer.WriteListBegin;
    {init the flag array and the position property of the TCollectionItem objects.}
    SetLength(ObjectWritten, Count);
    for i := 0 to Count - 1 do
    begin
      ObjectWritten[i] := False;
      Items[i].Position := i;
    end;
    {write the TCollectionItem objects. we write first the name of the objects class,
    then write all the object of the same class.}
    for i := 0 to Count - 1 do
    begin
      if ObjectWritten[i] then
        Continue;
      ItemClass := TUmbCollectionItemClass(Items[i].ClassType);
      Collection := TCollection.Create(ItemClass);
      CollectionList.Add(Collection);
      {write the items class name}
      Writer.WriteString(Items[i].ClassName);
      {insert the items to the collection}
      for j := i to Count - 1 do
        if ItemClass = Items[j].ClassType then
        begin
          ObjectWritten[j] := True;
          (Collection.Add as ItemClass).Assign(Items[j]);
        end;
      {write the collection}
      Writer.WriteCollection(Collection);
    end;
  finally
    CollectionList.Free;
    Writer.WriteListEnd;
    Writer.Free;
  end;
end;

{ TUmbCollectionItem }

procedure TUmbCollectionItem.Assign(Source: TPersistent);
begin
  if Source is TUmbCollectionItem then
    Position := (Source as TUmbCollectionItem).Position
  else
    inherited;
end;

end.





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