Dependency Injection for Windows Phone 7

Question

I was trying to use Unity 2.0 beta 2 for Silverlight in my Windows Phone 7 project and I kept getting this crash:

Microsoft.Practices.Unity.Silverlight.dll!Microsoft.Practices.ObjectBuilder2.DynamicMethodConstructorStrategy.DynamicMethodConstructorStrategy() + 0x1f bytes

Microsoft.Practices.Unity.Silverlight.dll!Microsoft.Practices.ObjectBuilder2.DynamicMethodConstructorStrategy.DynamicMethodConstructorStrategy() + 0x1f bytes   mscorlib.dll!System.Reflection.RuntimeConstructorInfo.InternalInvoke(System.Reflection.RuntimeConstructorInfo rtci = {System.Reflection.RuntimeConstructorInfo}, System.Reflection.BindingFlags invokeAttr = Default, System.Reflection.Binder binder = null, object parameters = {object[0]}, System.Globalization.CultureInfo culture = null, bool isBinderDefault = false, System.Reflection.Assembly caller = null, bool verifyAccess = true, ref System.Threading.StackCrawlMark stackMark = LookForMyCaller)  
mscorlib.dll!System.Reflection.RuntimeConstructorInfo.InternalInvoke(object obj = null, System.Reflection.BindingFlags invokeAttr = Default, System.Reflection.Binder binder = null, object[] parameters = {object[0]}, System.Globalization.CultureInfo culture = null, ref System.Threading.StackCrawlMark stackMark = LookForMyCaller) + 0x103 bytes 
mscorlib.dll!System.Activator.InternalCreateInstance(System.Type type = {Name = "DynamicMethodConstructorStrategy" FullName = "Microsoft.Practices.ObjectBuilder2.DynamicMethodConstructorStrategy"}, bool nonPublic = false, ref System.Threading.StackCrawlMark stackMark = LookForMyCaller) + 0xf0 bytes mscorlib.dll!System.Activator.CreateInstance() + 0xc bytes 
Microsoft.Practices.Unity.Silverlight.dll!Microsoft.Practices.ObjectBuilder2.StagedStrategyChain.AddNew(Microsoft.Practices.Unity.ObjectBuilder.UnityBuildStage stage = Creation) + 0x1d bytes    
Microsoft.Practices.Unity.Silverlight.dll!Microsoft.Practices.Unity.UnityDefaultStrategiesExtension.Initialize() + 0x6c bytes   
Microsoft.Practices.Unity.Silverlight.dll!Microsoft.Practices.Unity.UnityContainerExtension.InitializeExtension(Microsoft.Practices.Unity.ExtensionContext context = {Microsoft.Practices.Unity.UnityContainer.ExtensionContextImpl}) + 0x31 bytes  
Microsoft.Practices.Unity.Silverlight.dll!Microsoft.Practices.Unity.UnityContainer.AddExtension(Microsoft.Practices.Unity.UnityContainerExtension extension = {Microsoft.Practices.Unity.UnityDefaultStrategiesExtension}) + 0x1a bytes 
Microsoft.Practices.Unity.Silverlight.dll!Microsoft.Practices.Unity.UnityContainer.UnityContainer() + 0xf bytes 

Thinking I could resolve it I've tried a few things but to no avail.

Turns out that this is a rather fundamental problem and my assumption that Windows Phone 7 is Silverlight 3 + Some other stuff is wrong. This page describes the differences between Mobile Silverlight and Silverlight 3.

Of particular interest is this:

The System.Reflection.Emit namespace is not supported in Silverlight for Windows Phone.

This is precisely why Unity is crashing on the phone, DynamicMethodConstructorStrategy class uses System.Reflection.Emit quite extensively...

So the question is, what alternative to Unity is there for Windows Phone 7?

Answer 1

If you cannot find an IOC container that works on Windows Phone 7 (and I wouldn't be surprised you cannot) then I'd suggest going with a different DI strategy.

Answer 2

So, in the spirit of answering my own questions, I've put together a simple DI container (using Activator.CreateInstance for instantiating things). All this does is support type registrations and instance registrations.

Seems to be doing the job. Will worry about performance later.

public class DuplicateRegistrationException : Exception {
    public DuplicateRegistrationException() { }
    public DuplicateRegistrationException(string message) : base(message) { }
    public DuplicateRegistrationException(string message, Exception inner) : base(message, inner) { }
}

public interface IDIContainer {
    void Register<TIntf, TClass> () where TIntf: class where TClass : TIntf;
    TIntf Resolve<TIntf>() where TIntf : class;
    void RegisterInstance<TIntf>(TIntf instance);
}

public class DIContainer :  IDIContainer{

    Dictionary<Type, Type> m_TypeRegistrations;
    Dictionary<Type, object> m_InstanceRegistrations;

    public DIContainer() {
        m_TypeRegistrations = new Dictionary<Type, Type>();
        m_InstanceRegistrations = new Dictionary<Type, object>();
    }

    #region IDIContainer Members

    public void Register<TIntf, TClass>()
        where TIntf : class
        where TClass : TIntf {
            if(DoesRegistrationExist<TIntf>())
                throw new DuplicateRegistrationException("Can only contain one registration per type");
            m_TypeRegistrations.Add(typeof(TIntf), typeof(TClass));
    }

    public TIntf Resolve<TIntf>() where TIntf : class {
        return Resolve(typeof(TIntf)) as TIntf;
    }

    private object Resolve(Type type) {
        if(!m_TypeRegistrations.ContainsKey(type)) {
            if(!m_InstanceRegistrations.ContainsKey(type))
                throw new NotSupportedException("Cannot find registration for type " + type.FullName + ".");
            else
                return m_InstanceRegistrations[type];
        } else {
            var createdType = m_TypeRegistrations[type];

            ConstructorInfo[] constructors = createdType.GetConstructors();
            ConstructorInfo mostSpecificConstructor = null;
            foreach(var c in constructors) {
                if(mostSpecificConstructor == null || mostSpecificConstructor.GetParameters().Length < c.GetParameters().Length) {
                    mostSpecificConstructor = c;
                }
            }

            List<object> constructorParameters = new List<object>();
            foreach(var a in mostSpecificConstructor.GetParameters()) {
                constructorParameters.Add(Resolve(a.ParameterType));
            }

            return Activator.CreateInstance(createdType, constructorParameters.ToArray());
        }
    }

    private bool DoesRegistrationExist<T>() {
        return m_InstanceRegistrations.ContainsKey(typeof(T)) || m_TypeRegistrations.ContainsKey(typeof(T));
    }

    public void RegisterInstance<TIntf>(TIntf instance) {
        if(DoesRegistrationExist<TIntf>()) {
            throw new DuplicateRegistrationException("Can only contain one registration per type");
        }
        m_InstanceRegistrations.Add(typeof(TIntf), instance);
    }


    #endregion

Answer 3

I just started putting together a Windows Phone 7 Extension Tools project on codeplex. The current version checked in supports IoC with implicit DI along with the Common Service Locator to allow complete abstraction of your code and the container they use.

Check it out over at: http://wp7.codeplex.com

Cheers, Simon Hart