在MVC 3中提交时模型字符串属性为null

My model looks like:

我的模型看起来像：

public class MyViewModel
    {
        public MyViewModel()
        {
            MyClasses = new List<MyClass>();
        }

        public List<MyClass> MyClasses{ get; set; }

        [Required(ErrorMessage = "is required.")]
        public string Prop1{ get; set; }

        [Required(ErrorMessage = "is required.")]
        public int Prop2{ get; set; }
    }
public class