只要我的viewmodel只是一个具有直接属性的简单类,一切都可以正常工作
public class Foo
{
public int Bar {get;set;}
}
但是,DataAnnotationsModelBinder在尝试使用复杂的viewmodel时会导致NullReferenceException,例如
public class Foo
{
public class Baz
{
public int Bar {get;set;}
}
public Baz MyBazProperty {get;set;}
}
对于渲染多个LINQ实体的视图来说,这是一个很大的问题,因为我更喜欢使用包含多个LINQ实体而不是无类型ViewData数组的自定义viewmodel.
DefaultModelBinder没有这个问题,所以它似乎是DataAnnotationsModelBinder中的一个错误.这有什么解决方法吗？
编辑：一种可能的解决方法当然是在viewmodel类中公开子对象的属性,如下所示：
public class Foo
{
private Baz myBazInstance;
[required]
public string ExposedBar
{
get { return MyBaz.Bar; }
set { MyBaz.Bar = value; }
}
public Baz MyBaz
{
get { return myBazInstance ?? (myBazInstance = new Baz()); }
set { myBazInstance = value; }
}
#region Nested type: Baz
public class Baz
{
[required]
public string Bar { get; set; }
}
#endregion
}
#endregion
但我宁愿不必编写所有这些额外的代码. DefaultModelBinder可以正常使用这样的hiearchies,所以我认为DataAnnotationsModelBinder也应该如此.
第二次编辑：看起来这确实是DataAnnotationsModelBinder中的一个错误.但是,希望在下一个ASP.NET MVC框架版本发布之前可以修复它.有关详细信息,请参见this forum thread.
解决方法
我最终修改了DataAnnotationsModelBinder上的BindProperty来绕过NullReferenceException,我个人不喜欢只有绑定它们才有效(见下面的原因).
protected override void BindProperty(ControllerContext controllerContext,ModelBindingContext bindingContext,PropertyDescriptor propertyDescriptor) {
string fullPropertyKey = CreateSubPropertyName(bindingContext.ModelName,propertyDescriptor.Name);
// Only bind properties that are part of the request
if (bindingContext.ValueProvider.DoesAnyKeyHavePrefix(fullPropertyKey)) {
var innerContext = new ModelBindingContext() {
Model = propertyDescriptor.GetValue(bindingContext.Model),ModelName = fullPropertyKey,ModelState = bindingContext.ModelState,ModelType = propertyDescriptor.PropertyType,ValueProvider = bindingContext.ValueProvider
};
IModelBinder binder = Binders.GetBinder(propertyDescriptor.PropertyType);
object newPropertyValue = ConvertValue(propertyDescriptor,binder.BindModel(controllerContext,innerContext));
ModelState modelState = bindingContext.ModelState[fullPropertyKey];
if (modelState == null)
{
var keys = bindingContext.ValueProvider.FindKeysWithPrefix(fullPropertyKey);
if (keys != null && keys.Count() > 0)
modelState = bindingContext.ModelState[keys.First().Key];
}
// Only validate and bind if the property itself has no errors
//if (modelState.Errors.Count == 0) {
SetProperty(controllerContext,bindingContext,propertyDescriptor,newPropertyValue);
if (OnPropertyValidating(controllerContext,newPropertyValue)) {
OnPropertyValidated(controllerContext,newPropertyValue);
}
//}
// There was an error getting the value from the binder,which was probably a format
// exception (meaning,the data wasn't appropriate for the field)
if (modelState.Errors.Count != 0) {
foreach (var error in modelState.Errors.Where(err => err.ErrorMessage == "" && err.Exception != null).ToList()) {
for (var exception = error.Exception; exception != null; exception = exception.InnerException) {
if (exception is FormatException) {
string displayName = GetDisplayName(propertyDescriptor);
string errorMessage = InvalidValueFormatter(propertyDescriptor,modelState.Value.AttemptedValue,displayName);
modelState.Errors.Remove(error);
modelState.Errors.Add(errorMessage);
break;
}
}
}
}
}
}
我也对它进行了修改,以便它始终绑定属性上的数据,无论它是否有效.这样我就可以将模型传递回视图,而无需将无效属性重置为null.
控制器摘录
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(ProfileViewDataModel model)
{
FormCollection form = new FormCollection(this.Request.Form);
wsPerson service = new wsPerson();
Person newPerson = service.Select(1,-1);
if (ModelState.IsValid && TryUpdateModel<IPersonBindable>(newPerson,"Person",form.ToValueProvider()))
{
//call wsPerson.save(newPerson);
}
return View(model); //model.Person is always bound no null properties (unless they were null to begin with)
}
我的Model类(Person)来自web服务,所以我不能直接将属性放在它们上面,我解决这个问题的方法如下：
嵌套DataAnnotations的示例
[Validation.MetadataType(typeof(PersonValidation))] public partial class Person : IPersonBindable { } //force partial. public class PersonValidation { [Validation.Immutable] public int Id { get; set; } [Validation.required] public string FirstName { get; set; } [Validation.StringLength(35)] [Validation.required] public string LastName { get; set; } CategoryItemNullable NearestGeographicRegion { get; set; } } [Validation.MetadataType(typeof(CategoryItemNullableValidation))] public partial class CategoryItemNullable { } public class CategoryItemNullableValidation { [Validation.required] public string Text { get; set; } [Validation.Range(1,10)] public string Value { get; set; } }
现在,如果我将表单字段绑定到[ViewDataModel.] Person.NearestGeographicRegion.Text& [ViewDataModel.] Person.NearestGeographicRegion.Value ModelState开始正确验证它们,DataAnnotationsModelBinder也正确绑定它们.
这个答案不是决定性的,它是今天下午挠头的产物.
它没有经过适当的测试,尽管它已经通过了the project布莱恩威尔逊开始的单元测试,并且我自己进行了大部分有限的测试.为了真正关闭这个问题,我很想听听Brad Wilson关于这个解决方案的想法.
