Accessing a Service from within an XNA Content Pipeline Extension
- by David Wallace
I need to allow my content pipeline extension to use a pattern similar to a factory. I start with a dictionary type:
public delegate T Mapper<T>(MapFactory<T> mf, XElement d);
public class MapFactory<T>
{
Dictionary<string, Mapper<T>> map = new Dictionary<string, Mapper<T>>();
public void Add(string s, Mapper<T> m)
{
map.Add(s, m);
}
public T Get(XElement xe)
{
if (xe == null) throw new ArgumentNullException(
"Invalid document");
var key = xe.Name.ToString();
if (!map.ContainsKey(key)) throw new ArgumentException(
key + " is not a valid key.");
return map[key](this, xe);
}
public IEnumerable<T> GetAll(XElement xe)
{
if (xe == null) throw new ArgumentNullException(
"Invalid document");
foreach (var e in xe.Elements())
{
var val = e.Name.ToString();
if (map.ContainsKey(val))
yield return map[val](this, e);
}
}
}
Here is one type of object I want to store:
public partial class TestContent
{
// Test type
public string title;
// Once test if true
public bool once;
// Parameters
public Dictionary<string, object> args;
public TestContent()
{
title = string.Empty;
args = new Dictionary<string, object>();
}
public TestContent(XElement xe)
{
title = xe.Name.ToString();
args = new Dictionary<string, object>();
xe.ParseAttribute("once", once);
}
}
XElement.ParseAttribute is an extension method that works as one might expect. It returns a boolean that is true if successful.
The issue is that I have many different types of tests, each of which populates the object in a way unique to the specific test. The element name is the key to MapFactory's dictionary. This type of test, while atypical, illustrates my problem.
public class LogicTest : TestBase
{
string opkey;
List<TestBase> items;
public override bool Test(BehaviorArgs args)
{
if (items == null) return false;
if (items.Count == 0) return false;
bool result = items[0].Test(args);
for (int i = 1; i < items.Count; i++)
{
bool other = items[i].Test(args);
switch (opkey)
{
case "And":
result &= other;
if (!result) return false;
break;
case "Or":
result |= other;
if (result) return true;
break;
case "Xor":
result ^= other;
break;
case "Nand":
result = !(result & other);
break;
case "Nor":
result = !(result | other);
break;
default:
result = false;
break;
}
}
return result;
}
public static TestContent Build(MapFactory<TestContent> mf, XElement xe)
{
var result = new TestContent(xe);
string key = "Or";
xe.GetAttribute("op", key);
result.args.Add("key", key);
var names = mf.GetAll(xe).ToList();
if (names.Count() < 2) throw new ArgumentException(
"LogicTest requires at least two entries.");
result.args.Add("items", names);
return result;
}
}
My actual code is more involved as the factory has two dictionaries, one that turns an XElement into a content type to write and another used by the reader to create the actual game objects.
I need to build these factories in code because they map strings to delegates. I have a service that contains several of these factories. The mission is to make these factory classes available to a content processor. Neither the processor itself nor the context it uses as a parameter have any known hooks to attach an IServiceProvider or equivalent.
Any ideas?
