Running OpenNETCF 1.3 On NET PC

Since I'm porting a complex application framework from NET PC to NET CF I sometimes find it useful when debugging to run our NET CF code on the NET PC framework. This also comes in handy if, for instance, you want to run unit tests against your NET CF code on the desktop, since on-device automated testing is nearly impossible at this point. (There are sometimes major differences between the two implementations so this is not a good long-term strategy.)

The hardest part about this was getting OpenNETCF 1.3 to run on the desktop. Here's why: The OpenNETCF.Configuration.ConfigurationSettings class uses System.IO.Path internally when figuring out where to look for config files. It passes a Pocket PC compliant path string to Path.Combine() at one point, and, since the code is actually running on the NET PC framework, Path.Combine() throws an ArgumentException.

The only solution (short of rebuilding the OpenNETCF library) is to pre-install a different implementation of OpenNETCF.IConfigurationSystem before the default implementation is installed. There's no public API for installing your custom IConfigurationSystem; you must install it via reflection calls which bypass the restrictive access modifiers. (Obviously, this is a major hack not suitable for production code.) Here's an example of such an IConfigurationSystem implementation which simply passes configuration requests through to the standard NET PC ConfigurationSettings class:

using System;
using System.Reflection;
using ONETConfig = OpenNETCF.Configuration;
using MSConfig = System.Configuration;

namespace Test.PCUtil
{

  public class PassThruConfigSystem : ONETConfig.IConfigurationSystem
  {
  
    public static void InstallForOpenNETCF()
    {
      Type configSettingsType = typeof (ONETConfig.ConfigurationSettings);

      lock (configSettingsType)
      {
        // setting them again will cause an exception
        Object existingConfig = configSettingsType.InvokeMember(
          "configSystem",
          (BindingFlags.Static | 
            BindingFlags.NonPublic | 
            BindingFlags.GetField),
          null,
          null,
          null);

        if (existingConfig == null)
        {
          configSettingsType.InvokeMember(
            "SetConfigurationSystem",
            (BindingFlags.Static | 
              BindingFlags.NonPublic | 
              BindingFlags.InvokeMethod),
            null,
            null,
            new object[] {new PassThruConfigSystem()});
        }
      }
    }

    public PassThruConfigSystem()
    {
    }

    public object GetConfig(string configKey)
    {
      return MSConfig.ConfigurationSettings.GetConfig(configKey);
    }

    public void Init()
    {
    }
  }
}

In my next post I'll show you how to automatically install the PassThruConfigSystem when running unit tests with NUnit, which presents its own unique challenges!