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How to fix CAB to support dependencies across class hierarchy

The Composite UI Application Block’s Object Builder doesn’t support dependencies for same-named properties at different levels in the class hierarchy. If you add a dependency property which has the same name as a property in a base or derived class, only one of them will be initialized.

The reason for this is probably that the mechanism is based on the Type.GetProperties() method. This method doesn’t return all of the properties the class (and the base classes) contain – rather, it employs a “hide by name and signature” convention and gives only the topmost properties. So the first step we have to do is eliminate the GetProperties method. We do this by modifying the GetMembers() method of the PropertyReflectionStrategy (located in ObjectBuilder/Strategies/Property). It should look like this:

protected override IEnumerable<IReflectionMemberInfo<PropertyInfo>> GetMembers(IBuilderContext context, Type typeToBuild, object existing, string idToBuild)
{
    foreach (PropertyInfo propInfo in GetPropertiesFlattened(typeToBuild))
        yield return new PropertyReflectionMemberInfo(propInfo);
}

private IEnumerable<PropertyInfo> GetPropertiesFlattened(Type typeToBuild)
{
    for (Type t = typeToBuild; t != null; t = t.BaseType)
    {
        foreach (var pi in t.GetProperties(BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly)) // get only properties in this class
        {
            yield return pi;
        }
    }
}

The next problem arises because the PropertyReflectionStrategy keeps a dictionary of existing properties. It’s indexed by property name, which would eliminate our duplicate properties. We have to change it to use the full path - property name prefixed by class name and namespace. I did this by adding a property called FullName to the IReflectionMemberInfo and ReflectionMemberInfo (found in ObjectBuilder/Strategies).

In IReflectionMemberInfo, add:

string FullName { get; }

In ReflectionMemberInfo, add:

public string FullName
{
    get { return memberInfo.DeclaringType.FullName + "." + memberInfo.Name; }
}

There’s a PropertyReflectionMemberInfo class embedded in the PropertyReflectionStrategy, we have to add a similar property to it:

public string FullName
{
    get { return prop.DeclaringType.FullName + "." + prop.Name; }
}

Ok – next, in the PropertyReflectionStrategy we rewire the dictionary to use this new property. Go to AddParametersToPolicy method and change this -

if (!result.Properties.ContainsKey(member.Name))
    result.Properties.Add(member.Name, new PropertySetterInfo(member.MemberInfo, parameter));

- to this -

if (!result.Properties.ContainsKey(member.FullName))
    result.Properties.Add(member.FullName, new PropertySetterInfo(member.MemberInfo, parameter));

One last glitch to fix: go to CompositeUI/WorkItem class, and in the BuildUp() method change this -

propPolicy.Properties.Add("Parent", new PropertySetterInfo("Parent", new ValueParameter(typeof(WorkItem), null)));

- to this -

propPolicy.Properties.Add("Microsoft.Practices.CompositeUI.WorkItem.Parent", new PropertySetterInfo("Parent", new ValueParameter(typeof(WorkItem), null)));

Without this modification, the root WorkItem would have its Parent property reference itself, and it would not be recognized as root WorkItem because it’s Parent property is not null. As a consequence, some initialization methods would not get called and almost nothing would work.

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