C#学习教程：从自定义AdditionalMetadataAttribute访问模型类实例（asp.netmvc5）分享

我有以下情况 &＃8211; 我需要编写一个自定义的附加元数据属性，该属性基于另一个属性值（来自同一模型），向AdditionalValues字典添加一个值。 现在，我的问题是我无法访问属性类中的模型实例。

[AttributeUsage(AttributeTargets.Property)] public class ExtendedAdditionalMetadataAttribute : Attribute, IMetadataAware { #region Private properties private string extraFieldToCheck { get; set; } private string extraFieldValueToCheck { get; set; } private string fieldToBeAdded { get; set; } private string fieldValueToBeAdded { get; set; } #endregion #region Constructor public ExtendedAdditionalMetadataAttribute(string extraFieldToCheck, string extraFieldValueToCheck, string fieldToBeAdded, string fieldValueToBeAdded) { this.extraFieldToCheck = extraFieldToCheck; this.extraFieldValueToCheck = extraFieldValueToCheck; this.fieldToBeAdded = fieldToBeAdded; this.fieldValueToBeAdded = fieldValueToBeAdded; } #endregion public void OnMetadataCreated(ModelMetadata metadata) { // HOW TO GET THE MODEL CLASS INSTANCE??? // metadata.ContainerType is correct by metadata.Container is null. } } 

从代码注释中可以看出，在OnMetadataCreated中我需要访问Model类实例，但是尽管ContainerType是正确的，但Container属性是NULL。

能否通过给我一个关于这个问题的提示来帮助我？

先感谢您！

Evdin

稍后编辑

考虑到我没有给出太多解释，我还将在此处粘贴一个示例，说明我希望如何在模型类上使用此属性：

 /// 
 /// Gets or sets the IsAccountCreated /// 
 /// The IsAccountCreated. [UIHint("FormFieldStringTemplate")] [ExtendedAdditionalMetadata("IsExternalAccount", "true", "ReadOnly", "true")] public override Boolean IsAccountCreated { get; set; } /// 
 /// Gets or sets the IsAccountEnabled /// 
 /// The IsAccountEnabled. [Display(Name = "Este cont activ?")] [UIHint("FormFieldStringTemplate")] [ExtendedAdditionalMetadata("IsExternalAccount", "true", "ReadOnly", "true")] public override Boolean IsAccountEnabled { get; set; } /// 
 /// Gets or sets the IsExternalAccount /// 
 /// The IsExternalAccount. [Display(Name = "Este cont extern?")] [UIHint("FormFieldStringTemplate")] [AdditionalMetadata("ReadOnly", "true")] public override Boolean IsExternalAccount { get; set; } 

稍后和稍后编辑

虽然@ stephen-muecke给出的响应在当前情况下更简单和可接受，但为了编程挑战，我寻找其他选项，我发现了以下可能性：实现自定义DataAnnotationsModelMetadataProvider类。 用几个简单的单词 &＃8211; 它可以工作，只有当模型类是一个简单的类时我才能获得模型类实例BUT，否则有许多缺点 &＃8211; 例如，如果你有一个Model类并且你在视图中使用它那么没关系，但是如果你在另一个类（viewmodel中的模型）中有一个类，那么这种方法就不再可用了。

再次感谢@ stephen-muecke！

 namespace MyHelpers.Html { public static class ReadOnlyHelpers { public static MvcHtmlString ReadOnlyTextBoxIf(this HtmlHelper helper, Expression> expression, bool isReadOnly) { object attributes = isReadOnly ? new { @readOnly= "readonly" } : null; return InputExtensions.TextBoxFor(helper, expression, attributes); } } } 

 @Html.ReadOnlyTextBoxIf(m => m.SomeTextProperty, Model.SomeBooleanValue) 

 public static MvcHtmlString ReadOnlyCheckBoxIf(this HtmlHelper helper, Expression> expression, bool isReadOnly) { if (isReadOnly) { // If you want to 'visually' render a checkbox (otherwise just render a div with "YES" or "NO") ModelMetadata metaData = ModelMetadata.FromLambdaExpression(expression, helper.ViewData); StringBuilder html = new StringBuilder(); // Add a hidden input for postback html.Append(InputExtensions.HiddenFor(helper, expression).ToString()); // Add a visual checkbox without name so it does not post back TagBuilder checkbox = new TagBuilder("input"); checkbox.MergeAttribute("type", "checkbox"); checkbox.MergeAttribute("disabled", "disabled"); if ((bool)metaData.Model) { checkbox.MergeAttribute("checked", "checked"); } html.Append(checkbox.ToString()); return MvcHtmlString.Create(html.ToString()); } else { // return normal checkbox return InputExtensions.CheckBoxFor(helper, expression); } } 

 @Html.ReadOnlyCheckBoxIf(m => m.IsAccountCreated, Model.IsExternalAccount)