Implements IModelBinder 为啥总是报错

Implements IModelBinder 为什么总是报错？

Public Class ModelBinder
            Implements IModelBinder
            Function BindModel(controllerContext As ControllerContext, bindingContext As ModelBindingContext) As Object
                Dim request = controllerContext.RequestContext.HttpContext.Request
                Dim formUpload = request.Files.Count > 0

                ' find filename
                Dim xFileName = request.Headers("X-File-Name")
                Dim qqFile = request("qqfile")
                Dim formFilename = If(formUpload, request.Files(0).FileName, Nothing)

                Dim upload = New FineUpload() With { _
                    .Filename = If(xFileName, If(qqFile, formFilename)), _
                    .InputStream = If(formUpload, request.Files(0).InputStream, request.InputStream) _
                }

                Return upload
            End Function
        End Class

这句话怎么总是报错？
错误 2 Class“ModelBinder”必须为接口“System.Web.Mvc.IModelBinder”实现“Function BindModel(controllerContext As ControllerContext, bindingContext As ModelBindingContext) As Object”。 C:\Users\KYO\Documents\Visual Studio 2012\Projects\MvcApplication3\MvcApplication3\Models\FineUpload.vb 25 24 MvcApplication3

------解决思路----------------------
你忘记写 Implements .IModelBinder.BindModel了