Model Binder in MVC:
http://msdn.microsoft.com/en-us/library/dd410405%28v=vs.100%29.aspx
"A model binder in MVC provides a simple way to map posted form values
to a .NET Framework type and pass the type to an action method as a
parameter. Binders also give you control over the deserialization of
types that are passed to action methods. Model binders are like type
converters, because they can convert HTTP requests into objects that are
passed to an action method. However, they also have information about
the current controller context."
One
item I take for granted when I'm using ASP.NET MVC is the powerful
feature that is model binding. Model binding is ASP.NET MVC's mechanism
for mapping HTTP request data directly into action method parameters and
custom .Net objects. Each time your application receives an HTTP
request containing the form's data as a pair of key/value pairs, the ControllerActionInvoker invokes the DefaultModelBinder
to transform that raw HTTP request into something more meaningful to
you, which would be a .Net object. This just works and I love
it. Sometimes you need to customize the default model binding to work a
little differently. For example, if you were expecting a strongly typed
collection of values posted from a multi select control, the default
model binding won't work as expected. I'll demonstrate one workaround
for this so your action can expect a strongly typed object, and not just
an array of strings.
Open
visual studio 2010 and create a new ASP.NET MVC 2 empty web
application. The model for this will be simple as I want to illustrate
the technique of model binding. Here's the model below:
public class Car
{
public string Make { get; set; }
public int Id { get; set; }
public static List<Car> GetCars()
{
return new List<Car>
{
new Car { Id = 1, Make = "Ford"},
new Car { Id = 2, Make = "Holden"},
new Car { Id = 3, Make = "Chevrolet"}
};
}
}
Now to fast track things. I've got an action that receives HTTP post request and its signature is below:
[HttpPost]
public ActionResult PostCars(List<Car> cars)
{
return Content("Ok");
}
The
action's parameter is a generic list of Car objects. If you post the
data using a multi select HTML control, the default model binding won't
work as expected.
The
model binder doesn’t know how to bind the incoming values to a generic
list of cars. This is where you can create a custom model binder to do
this for you. To create a custom model binder, all that’s required is a
class that inherits the IModelBinder interface. From there you implement the BindModel method. Here’s the code below:
public class SelectListModelBinder : IModelBinder
{
public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
// Get the raw attempted value from the value provider
var incomingData = bindingContext.ValueProvider.GetValue("cars").AttemptedValue;
return incomingData.Split(new char[1] { ',' }).Select(data => Car.GetCars().FirstOrDefault(o => o.Id == int.Parse(data))).ToList();
}
}
The incoming data can be viewed thanks to the binding context parameter:
var incomingData = bindingContext.ValueProvider.GetValue("cars").AttemptedValue;
The
cars values is being passed into the action through the
Request.Forms["cars"] value. From there I return a Car object populated
with the values from incoming data. Nice and easy.
To
use this function I can either register the model binder in the
global.asax file, which means it will available to any action that
accept a list of cars:
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
ModelBinders.Binders.Add(typeof (List<Car>), new SelectListModelBinder());
RegisterRoutes(RouteTable.Routes);
}
If I wanted to target particular actions, I can prefix the model binder to the parameter:
public ActionResult PostCars([ModelBinder(typeof(SelectListModelBinder))] List<Car> cars)
{
return Content("Ok");
}
Model binding is a powerful feature in ASP.NET MVC and it can help you out in sticky situations.
All the demo related with mvc please click here
Source of this post:http://www.dotnetcurry.com/showarticle.aspx?ID=584
