Create polymorphic object without IF clause
I have an abstract class:
public abstract class Records
{
public string Type;
public string Source;
public int Value;
protected Records(string type, string source, int value)
{
Type = type;
Source = source;
Value = value;
}
}
I would like to create many classes that inherit from this class and fill their Type field with the value coming from the static class like this:
public static class ContentTypesString
{
public static string DocumentNew { get { return "Document - New this Month"; }}
public static string HeadlinesNew { get { return "Headlines - New this Month"; }}
etc...
}
I would like to be able to create these child classes without test " if foo == "document" then type = ContentTypesString.DocumentNew
" or equivalent switch code (I do have many cases indeed)
Is there a design template that suits my needs?
EDIT: As several people pointed out, I have to show how I create my instances.
private delegate SPListItemCollection Query(SPWeb web, DateTime startDate, DateTime endDate);
private readonly Query _queries;
#region Constructors
public QueryHandler(SPWeb web, DateTime startTimeSelectedDate, DateTime endTimeSelectedDate)
{
if (web == null) throw new ArgumentNullException("web");
_web = web;
_startTimeSelectedDate = startTimeSelectedDate;
_endTimeSelectedDate = endTimeSelectedDate;
RecordsList = new List<Records>();
// Query Invocation List
_queries = NumberPagePerMonthQuery.PreparedQuery;
_queries += NumberDocumentsPerMonthQuery.PreparedQuery;
_queries += NumberHeadlinesPerMonthQuery.PreparedQuery;
_queries += NumberLeaderboxPerMonthQuery.PreparedQuery;
_queries += NumberNewsPerMonthQuery.PreparedQuery;
_queries += NumberPagesModifiedPerMonthQuery.PreparedQuery;
_queries += NumberPicturesPerMonthQuery.PreparedQuery;
_queries += NumberTeasingPerMonthQuery.PreparedQuery;
}
#endregion Constructors
#region Public Methods
// what about NullReferenceException ? C#6 : item?.Foreach(item => {}); ?
/*** NO C#6 compiler in VS2012... ***/
public void Queries()
{
foreach (var del in _queries.GetInvocationList())
{
var queryresult =
(SPListItemCollection) del.DynamicInvoke(_web, _startTimeSelectedDate, _endTimeSelectedDate);
RecordsList.Add(new Records(del.Method.Name, _web.Title, queryresult.Count));
}
}
EDIT² : Solution I chose
public List<IQuery> QueryList { get; } // no delegate anymore, and static classes became implementations of IQuery interface.
#region Constructors
public QueryHandler(SPWeb web, DateTime startTimeSelectedDate, DateTime endTimeSelectedDate)
{
if (web == null) throw new ArgumentNullException("web");
_web = web;
_startTimeSelectedDate = startTimeSelectedDate;
_endTimeSelectedDate = endTimeSelectedDate;
RecordsList = new List<Records>();
QueryList = new List<IQuery>
{
new NumberDocumentsPerMonthQuery(),
new NumberHeadlinesPerMonthQuery(),
new NumberLeaderboxPerMonthQuery(),
new NumberNewsPerMonthQuery(),
new NumberPagePerMonthQuery(),
new NumberPagesModifiedPerMonthQuery(),
new NumberPicturesPerMonthQuery(),
new NumberTeasingPerMonthQuery()
};
}
#endregion Constructors
#region Public Methods
// what about NullReferenceException ? C#6 : item?.Foreach(item => {}); ?
/*** NO C#6 compiler in VS2012... ***/
public void Queries()
{
foreach (var query in QueryList)
{
var queryresult = query.PreparedQuery(_web, _startTimeSelectedDate, _endTimeSelectedDate);
RecordsList.Add(query.CreateRecord(_web.Title, queryresult.Count));
}
}
The writer class follows the implementation suggested by @dbraillon To implement the IQuery interface, a method has been added:
public Records CreateRecord(string source, int value)
{
return new ModifiedPagesPerMonthRecord(source, value); //or another child of Record class.
}
And voila. Thanks everyone for the help.
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2 answers
You want to make the collection of records, object type string code and parameters.
One of the many ways to do this is to use a builder.
First, we need to configure the builder:
var builder = new RecordBuilder()
.RegisterBuilder("document", (source, value) => new Document(source, value))
.RegisterBuilder("headlines", (source, value) => new Headlines(source, value));
here we will show you how to create an entry with the code "document" and "headers".
To create a recording call:
builder.Build("document", "source", 1);
The Builder code could be something like this (here we are looking to see if we know how to create a past type record and do it):
public class RecordBuilder
{
public Records Build(string code, string source, int value)
{
Func<string, int, Records> buildAction;
if (recordBuilders.TryGetValue(code, out buildAction))
{
return buildAction(source, value);
}
return null;
}
public RecordBuilder RegisterBuilder(string code, Func<string, int, Records> buildAction)
{
recordBuilders.Add(code, buildAction);
return this;
}
private Dictionary<string, Func<string, int, Records>> recordBuilders = new Dictionary<string, Func<string, int, Records>> ();
}
public class Document : Records
{
public Document(string source, int value) : base(ContentTypesString.DocumentNew, source, value)
{
}
}
public class Headlines : Records
{
public Headlines(string source, int value) : base(ContentTypesString.HeadlinesNew, source, value)
{
}
}
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This is what you need?
public abstract class Records
{
public string Type;
public string Source;
public int Value;
protected Records(string type, string source, int value)
{
Type = type;
Source = source;
Value = value;
}
}
public class DocumentRecords : Records
{
public DocumentRecords(string source, int value)
: base(ContentTypesString.DocumentNew, source, value) // use here
{
}
}
public class HeadlinesRecords : Records
{
public HeadlinesRecords(string source, int value)
: base(ContentTypesString.HeadlinesNew, source, value) // use here
{
}
}
public static class ContentTypesString
{
public static string DocumentNew { get { return "Document - New this Month"; } }
public static string HeadlinesNew { get { return "Headlines - New this Month"; } }
}
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