Another .NET Blog

To implement this behavior, we just have to replace the public static Func property LocateForModelType of the ViewLocator class.

In order to let the source files of CM intact, I will create a new static class ViewLocatorConfigurator, with a Configure method, which will "override" the default behavior of the LocateForModelType method. And to activate this custom behavior, I will just have to call this method in the Configure method of the BootStrapper.

But before I show you this class, let's create the attribute which will be used:

[DebuggerStepThrough]
[AttributeUsage(AttributeTargets.Class)]
public class UseViewAttribute : Attribute
{
    private readonly string viewName;

    public UseViewAttribute(string viewName)
    {
        Contract.Requires(!string.IsNullOrEmpty(viewName));
        Contract.Ensures(ViewName != null);

        this.viewName = viewName;
    }

    [ContractInvariantMethod]
    private void ObjectInvariant()
    {
        Contract.Invariant(ViewName != null);
    }

    public string ViewName { [DebuggerStepThrough] get { return viewName; } }
}

Nothing fancy, we just have to specify the name of the view.

Now, let's see how to use this attribute in our new definition of LocateForModelType:

public static class ViewLocatorConfigurator
{
    public static void Configure()
    {
        ViewLocator.LocateForModelType = (modelType, displayLocation, context) =>
                                {
                                    var useViewAttributes = modelType.GetCustomAttributes(typeof(UseViewAttribute), true)
                                        .Cast<UseViewAttribute>();
                                        
                                    Contract.Assert(useViewAttributes.Count() <= 1, "There can only be zero or one UseViewAttribute on a view model");

                                    string viewTypeName;
                                        
                                    if (useViewAttributes.Count() == 1)
                                        viewTypeName = string.Concat(modelType.Namespace.Replace("Model", string.Empty), ".", useViewAttributes.First().ViewName);
                                    else
                                    {
                                        viewTypeName = modelType.FullName.Replace("Model", string.Empty);
                                        if (context != null)
                                        {
                                            viewTypeName = viewTypeName.Remove(viewTypeName.Length - 4, 4);
                                            viewTypeName = viewTypeName + "." + context;
                                        }
                                    }

                                    var viewType = (from assembly in AssemblySource.Instance
                                                    from type in assembly.GetExportedTypes()
                                                    where type.FullName == viewTypeName
                                                    select type).FirstOrDefault();

                                    return viewType == null
                                                ? new TextBlock {Text = string.Format("{0} not found.", viewTypeName)}
                                                : ViewLocator.GetOrCreateViewType(viewType);
                                };
    }
}

I don't think this needs a lot of explanations. I just check there is only zero or one UseViewAttribute on top of the VM, and I create the full name of the view, based on the namespace of the VM and the name of the view given in parameter to the attribute. And I use the same code as the original version to create the view.

This was a short article, but I hope you enjoyed it, and that it will convince you of the power of Caliburn Micro.

See you soon!