{
* UNews.pas
*
* Maintains a list of news items for display by program and reads list from
* formatted data stream.
*
* $Rev$
* $Date$
*
* ***** BEGIN LICENSE BLOCK *****
*
* Version: MPL 1.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for
* the specific language governing rights and limitations under the License.
*
* The Original Code is UNews.pas
*
* The Initial Developer of the Original Code is Peter Johnson
* (http://www.delphidabbler.com/).
*
* Portions created by the Initial Developer are Copyright (C) 2006-2010 Peter
* Johnson. All Rights Reserved.
*
* Contributor(s)
* NONE
*
* ***** END LICENSE BLOCK *****
}
unit UNews;
interface
uses
// Delphi
Classes,
// Project
UDataStreamIO, ULists;
type
{
TNewsItem:
Encapsulates a news item. Provides properties to describe it and a means
of creating object from a formatted data stream.
}
TNewsItem = class(TObject)
strict private
var
fId: SmallInt; // Value of Id property
fDate: TDateTime; // Value of Date property
fHTML: string; // Value of HTML property
public
constructor Create(const Reader: TDataStreamReader);
{Class constructor. Creates news item object from a data stream.
@param Reader [in] Object used to read/parse data stream.
}
property Id: SmallInt read fId;
{Unique identifier of news item}
property Date: TDateTime read fDate;
{Date news item published}
property HTML: string read fHTML;
{News item content as HTML}
end;
{
TNews:
Stores news items for display in application. Parses news items from a
data stream supplied to constructor.
}
TNews = class(TObject)
strict private
type
TEnumerator = class(TObject)
strict private
var
fNews: TNews; // Reference to object being enumerated
fIndex: Integer; // Index of current object in enumeration
public
constructor Create(const News: TNews);
{Class constructor. Initialises enumeration.
@param News [in] Object to be enurmerated.
}
function GetCurrent: TNewsItem;
{Gets current news item.
@return Required name.
}
function MoveNext: Boolean;
{Moves to next item in enumeration.
@return True if there is a next item, False if beyond last item.
}
property Current: TNewsItem read GetCurrent;
{Current news item}
end;
var
fNewsItems: TObjectListEx; // Stores list of news items
procedure Parse(const NewsData: TStream);
{Creates list of news items from a data stream.
@param NewsData [in] Data stream containing news items.
}
function GetCount: Integer;
{Read accessor for Count property.
@return Number of news items in list.
}
function GetItem(Idx: Integer): TNewsItem;
{Read accessor for Items[] property.
@param Idx [in] Index of required item.
@return Requested news item.
}
public
constructor Create(const NewsData: TStream);
{Class constructor. Creates list of news items described by a data stream.
@param NewsData [in] Stream containing news items.
}
destructor Destroy; override;
{Class destructor. Tears down object.
}
function GetEnumerator: TEnumerator;
{Creates an enumerator for this object.
@return Reference to new enumerator. Caller is repsonsible for freeing
this object.
}
property Count: Integer read GetCount;
{Number of news items in list}
property Items[Idx: Integer]: TNewsItem read GetItem; default;
{Array of news items}
end;
implementation
uses
// Delphi
SysUtils,
// Project
UUtils;
{
News data stream format
-----------------------
Stream compriises text characters. Numbers are encoded in hex format.
File format is:
Item-count: SmallInt - number of news items in stream
followed by Item-count news item records:
Id: SmallInt - unique item identifier
Date: SizedString - publication date as MySQL date (YYYY-MM-DD)
Content: SizedString - news item content as HTML
Data types are:
SmallInt - 16 bit integer encoded as 4 hex digits
SizedString - SmallInt specifying string length followed by specified
number of characters
}
{ TNews }
constructor TNews.Create(const NewsData: TStream);
{Class constructor. Creates list of news items described by a data stream.
@param NewsData [in] Stream containing news items.
}
begin
inherited Create;
fNewsItems := TObjectListEx.Create(True);
Parse(NewsData);
end;
destructor TNews.Destroy;
{Class destructor. Tears down object.
}
begin
FreeAndNil(fNewsItems); // frees news items in list
inherited;
end;
function TNews.GetCount: Integer;
{Read accessor for Count property.
@return Number of news items in list.
}
begin
Result := fNewsItems.Count;
end;
function TNews.GetEnumerator: TEnumerator;
{Creates an enumerator for this object.
@return Reference to new enumerator. Caller is repsonsible for freeing this
object.
}
begin
Result := TEnumerator.Create(Self);
end;
function TNews.GetItem(Idx: Integer): TNewsItem;
{Read accessor for Items[] property.
@param Idx [in] Index of required item.
@return Requested news item.
}
begin
Result := fNewsItems[Idx] as TNewsItem;
end;
procedure TNews.Parse(const NewsData: TStream);
{Creates list of news items from a data stream.
@param NewsData [in] Data stream containing news items.
}
var
Reader: TDataStreamReader; // object used to interpret data stream
NumItems: SmallInt; // number of news items to create
Idx: Integer; // loops thru news items
begin
Reader := TDataStreamReader.Create(NewsData);
try
// Get number of items in data stream
NumItems := Reader.ReadSmallInt;
// Create required number of news items from stream
for Idx := 1 to NumItems do
fNewsItems.Add(TNewsItem.Create(Reader))
finally
FreeAndNil(Reader);
end;
end;
{ TNews.TEnumerator }
constructor TNews.TEnumerator.Create(const News: TNews);
{Class constructor. Initialises enumeration.
@param News [in] Object to be enurmerated.
}
begin
inherited Create;
fIndex := -1;
fNews := News;
end;
function TNews.TEnumerator.GetCurrent: TNewsItem;
{Gets current news item.
@return Required name.
}
begin
Result := fNews[fIndex];
end;
function TNews.TEnumerator.MoveNext: Boolean;
{Moves to next item in enumeration.
@return True if there is a next item, False if beyond last item.
}
begin
Result := fIndex < Pred(fNews.Count);
if Result then
Inc(fIndex);
end;
{ TNewsItem }
constructor TNewsItem.Create(const Reader: TDataStreamReader);
{Class constructor. Creates news item object from a data stream.
@param Reader [in] Object used to read/parse data stream.
}
begin
inherited Create;
// Get property values from stream. Order is important
fId := Reader.ReadSmallInt;
fDate := MySQLDateToDateTime(string(Reader.ReadSizedString));
fHTML := string(Reader.ReadSizedString);
end;
end.
