问题
I have created a new ActionFilter for an ASP.NET MVC application that I'm creating. I have an action which accepts an Http Post and the argument of the action method accepts an object, for which I have created and registered a custom model binder.
I noticed that inside the IActionFilter.OnActionExecuting the value for filterContext.Controller.ViewData.Model is always null despite the fact that it looks like the model binder is always invoked before the action filter OnActionExecuting method. In contrast to this inside the IActionFilter.OnActionExecuted method of the same action filter the value for filterContext.Controller.ViewData.Model is not null.
Do you guys know if this is by design or a bug? If by design are their any links which describe why this is? Thanks.
回答1:
Since the Controller Action is responsible for creating the Model and passing it to the View how could the Model exist prior to the action being called? You don't know what Model is going to be created until after it's happened.
回答2:
Sayed, you usually set a model during the execution of an action. Therefore, it is natural that the model is null during the execution of the OnActionExecuting which occurs before the action is called.
来源：https://stackoverflow.com/questions/2444956/model-availability-inside-actionfilter