2005 2006 2007 2008 2009 2010 2011 2015 2016 2017 2018 aspnet azure csharp debugging docker elasticsearch exceptions firefox javascriptajax linux llblgen mongodb powershell projects python security services silverlight training videos wcf wpf xag xhtmlcss

New XAG Feature - Better Generics

In the original release of XAG, properties could be generic only by using aliases. That is, if you wanted to have a property with a type of "Collection<Item>" you would have to create an alias like this:

using LineItemsCollection = System.Collections.ObjectModel.Collection<XagNewGenericsExample.Item>;


private LineItemsCollection lineitems;

public LineItemsCollection LineItems {
    get { return lineitems; }
    set { lineitems = value; }

which in XAG's markup looked like this:

  <Alias x:Key="LineItemsCollection" Name="Whatever" Type="System.Collections.ObjectModel.Collection[{Type Item}]" />
  <LineItems Type="{Type LineItemsCollection}" />

That's not really a bad deal as it really helps to enforce proper type design. For example, many times I will see people doing this:

public class MyAlias : Collection<Item> {}

MyAlias is NOT an alias for Collection<Item>. Try to compare them in code, they won't match up. However, in the first example "LineItemsCollection" and "Collection<Item>" are the same.

That said, I wanted to add something a bit more flexible. So I wrote an extension markup subsystem for XAG that allows for more complex generics. Here's an example of a property using the new generics system (assuming you have the System.Collections.ObjectModel namespace in):

<LineItems Type="{GenericType Name=Collection, Types=({Type Item})}" />

As you can see it's completely inline. Now here's a more complex example:

<ComplexItems Type="{GenericType Name=Dictionary, Types=(Int32, {GenericType Name=Collection, Types=({Type Item})})}" />

This XAG property translates to the following C# property:

private Dictionary<Int32, Collection<Item>> complexitems;

public Dictionary<Int32, Collection<Item>> ComplexItems {
    get { return complexitems; }
    set { complexitems = value; }

Here's a complete example you can try on your own.

<Assembly xmlns:x="http://www.jampadtechnology.com/xag/2006/11/" DefaultNamespace="XagNewGenericsExample">
  <Item x:Key="Item" Type="Class" AccessModifier="Public" />
  <ItemSet x:Key="ItemSet" Type="Class" AccessModifier="Public">
      <Import Name="System.Collections.Generic" />
      <Import Name="System.Collections.ObjectModel" />
      <Items Type="{GenericType Name=Collection, Types=({Type Item})}" />
      <ComplexItems Type="{GenericType Name=Dictionary, Types=(Int32, {GenericType Name=Collection, Types=({Type Item})})}" />
So now you an have more complex generic types in your XAG structure.