RequiredIf GetProperty空引用

Question

我有一个只对来宾显示的表单字段，如果它对来宾可显示，则是必需的。我遇到的问题是Extension.cs type.GetProperty(PropertyName)返回null，这会使整行返回一个null引用异常。我花了一些时间研究可能导致这种情况的原因，比如确保属性是公共的，实际上是一个属性，等等，但我被难住了。

Page.html.cs

 public bool IsGuest { get; set; } 

 [BindProperty]
 [RequiredIfTrue(nameof(IsGuest), ErrorMessage = "Please enter a valid email address.")]
 [EmailAddress]
  public string GuestEmail { get; set; }

     public IActionResult OnGet()
     {
        var claimsIdentity = (ClaimsIdentity)User.Identity;
            var claim = "";
            if (claimsIdentity.Claims.Any())
            {
                claim = claimsIdentity.FindFirst(ClaimTypes.NameIdentifier).Value;
                IsGuest = false;
            }
            else
            {
                IsGuest = true;
                claim = Request.Cookies[".AspNetCore.Session"];
            }
      }

Extention.cs

 public class RequiredIfTrueAttribute : RequiredAttribute
{
    private string PropertyName { get; set; }

    public RequiredIfTrueAttribute(string propertyName)
    {
        PropertyName = propertyName;
    }

    protected override ValidationResult IsValid(object value, ValidationContext context)
    {
        object instance = context.ObjectInstance;
        Type type = instance.GetType();

        bool.TryParse(type.GetProperty(PropertyName).GetValue(instance)?.ToString(), out bool propertyValue);

        if (propertyValue && string.IsNullOrWhiteSpace(value?.ToString()))
        {
            return new ValidationResult(ErrorMessage);
        }

        return ValidationResult.Success;
    }
}

Answer 1

我遇到的问题是

Extension.cs type.GetProperty(PropertyName)返回null，这会使整行返回一个null引用异常。

这是因为context.ObjectInstance.GetType()返回对象类型，您不能反向从对象获取IsGuest属性，所以它返回null。

为了能够正常使用RequiredIfTrueAttribute，您可以将IsGuest和GuestEmail字段放入一个类中，然后在页面中将该类作为属性引用。

下面是一个基于您的代码的简单示例：

public class MyModel
    {
        public bool IsGuest { get; set; }
        [RequiredIfTrue(nameof(IsGuest), ErrorMessage = "Please enter a valid email address.")]
        [EmailAddress]
        public string GuestEmail { get; set; }
    }

页面：

   public class AttrTestModel : PageModel
    {
        [BindProperty]
        public MyModel data { get; set; } = new MyModel();

        public void OnGet()
        {
            var claimsIdentity = (ClaimsIdentity)User.Identity;
            var claim = "";
            if (claimsIdentity.Claims.Any())
            {
                claim = claimsIdentity.FindFirst(ClaimTypes.NameIdentifier).Value;
                data.IsGuest = false;
            }
            else
            {
                data.IsGuest = true;
                claim = Request.Cookies[".AspNetCore.Session"];
            }
        }
        public void OnPost()
        {

        }
    }

查看：

@page
@model WebApplication_razorpage_new.Pages.AttrTestModel
@{
    ViewData["Title"] = "AttrTest";
}

<h1>AttrTest</h1>
<form method="post">
    <div class="form-group">
        <label asp-for="@Model.data.IsGuest" class="control-label"></label>
        <input id="Radio1" type="radio" asp-for="@Model.data.IsGuest" value="@Model.data.IsGuest" />
    </div>
    @if (Model.data.IsGuest)
    {
        <div class="form-group">
            <label asp-for="@Model.data.GuestEmail" class="control-label"></label>
            <input asp-for="@Model.data.GuestEmail" class="form-control" />
            <span asp-validation-for="@Model.data.GuestEmail" class="text-danger"></span>
        </div>
    }
    <input id="Submit1" type="submit" value="submit" />
</form>

测试结果如下：

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