Tuesday, June 9, 2009

Generic Type Conversion

While working on the Virtual Earth map application, I discovered the need to parse data from a string of characters. So I searched the net and found this answer on stack overflow: generic-type-conversion-from-string . I like this code example because it looks like the simplest and most general approach:

public class TypedProperty<T> : Property
public T TypedValue
get { return (T)Convert.ChangeType(base.Value, typeof(T)); }
set { base.Value = value.ToString();}
But if you cut and paste the code into a Silverlight 2 or Silverlight 3 application it does not run. This is because the two argument version of the ChangeType method is not part of the Silverlight runtime. I guess I could have used the three argument version, but instead I implemented a function the uses reflection:

public bool TryParse<T>(string sValue, out T oValue) where T : IConvertible
oValue = default(T);

string[] parts = sValue.Split(':');
MethodInfo oMethod = typeof(T).GetMethod("Parse", new Type[] { typeof(string) } );
oValue = (T)oMethod.Invoke(null, new object[] { parts[1].Trim() });
return true;
catch { }
return false;
Silverlight Size vs. Functionality

You find this all the time in Silverlight development -- some of the tools, functions and features you have come to rely on in .NET are just not part of the lightweight Silverlight runtime. I read on one blog that programming with Silverlight is like going camping with .NET. In fact, I first learned this the hard way trying to recompile some previous .NET code. I couldn't include the existing library -- it had to be rebuilt using the Silverlight libraries. When I attempted to recompile it, I found that it needed to be reengineered to use functionality available in the Silverlight runtime.

I have always been able to find a creative solution to simple programming issues like the one above, and I think the ability to deliver my solution over the web to any machine, without creating a custom install, makes it worth the effort to find these alternative approaches.

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