Ninject: Implement WithConstructorArgument(string name, Func<IContext,object> callback)

Question

I have a MVVM WP7 app in which I'm trying to send a value from one Page/ViewModel to the contructor of a second ViewModel. I already have Ninject set up and got this to work with a static test value using a line such as:

this.Bind<TaskViewModel>().ToSelf().WithConstructorArgument("TaskID", 2690)

Again, that works with a static value but I need it to be a variable selected by the user. I've been told to use the overload

WithConstructorArgument(string name, Func<IContext,object> callback). 

I would think that this callback would call a function on the first ViewModel and get the value.

But I have not been successful, readily admitting I am not very experienced in either Ninject or using a Func callback argument. I've tried setting up a delegate and function to get the value from the first ViewModel but that gives an error saying I'm trying to pass in a type. How exactly do I specify that argument to use a callback and am I correct to use a delegate in the first ViewModel or something else?

Answer 1

As I already said in your other post passing the argument on get is probably the better way. Therefor create a factory interface

public interface ITaskViewFactory
{
    TaskViewModel CreateTaskViewModel(int id);
}

In your bootstrapper (The assembly responsible to create everything using Ninject, which should normally be another one than where you implement everything with business value) add the implementation

Public class TaskViewFactory : ITaskViewFactory
{
     Private IKernel kernel;
     Public TaskViewFactory(IKernel kernel)
     {
         this.kernel = kernel;
     }

     public TaskViewModel CreateTaskViewModel(int taskId)
     {
         this.kernel.Get<ITaskViewModel>(new ConstructorArgument("TaskId", taskId);
     }
 }

Then inject the factory to your task selection command and call the factory whena task is selected.