无法获取自定义属性值在HTML MVC3助手 [英] Can't get Custom Attribute Value in MVC3 HTML Helper

问题描述

我扩展HTML辅助与需要从模型的属性的属性值的方法。所以，我已经定义了一个自定义属性本身。

 公共类ChangeLogFieldAttribute：属性{
        公共字符串字段名{获得;组; }
    }
 

它的使用方法是在我的模型。

  [显示（NAME =风格）]
    [ChangeLogField（字段名=styleid）]
    公共字符串样式{搞定;组; }
 

在我的辅助方法，我有以下code，让我的属性的字段名的值，如果使用该属性的属性。

  VAR ITEMNAME =（（MemberEx pression）ex.Body）.Member.Name;        VAR containerType = html.ViewData.ModelMetadata.ContainerType;
        var属性= ((ChangeLogFieldAttribute[])containerType.GetProperty(html.ViewData.ModelMetadata.PropertyName).GetCustomAttributes(typeof(ChangeLogFieldAttribute), FALSE））FirstOrDefault（）。
        如果（属性！= NULL）{
            ITEMNAME = attribute.FieldName;
        }
 

然而，当我达到这个code，我得到一个异常，因为containerType为null。

我不知道如果我做任何这是正确的，但我从大约4个不同来源扯远得到这个。如果你能提出一个修正我的问题或替代方案，我会很感激。

感谢。

与Solution更新

我用达林季米特洛夫的解决方案，尽管我不得不调整它的一些。下面是我加的。我不得不检查属性metatdata的存在，一切都很好。

  VAR字段名=（（MemberEx pression）ex.Body）.Member.Name;        VAR元= ModelMetadata.FromLambdaEx pression（例如，html.ViewData）;
        如果（metadata.AdditionalValues​​.ContainsKey（fieldName的））{
            字段名=（字符串）metadata.AdditionalValues​​ [字段名];
        }
 

解决方案

您可以使属性的元数据清楚：

 公共类ChangeLogFieldAttribute：属性，IMet​​adataAware
{
    公共字符串字段名{获得;组; }    公共无效OnMetadataCreated（ModelMetadata元数据）
    {
        metadata.AdditionalValues​​ [字段名] =字段名;
    }
}
 

，然后助手里面的：

  VAR元= ModelMetadata.FromLambdaEx pression（例如，htmlHelper.ViewData）;
VAR字段名= metadata.AdditionalValues​​ [字段名];
 

I've extended the HTML helper with a method that needs an attribute value from the property of the model. So I've defined a custom attribute as such.

    public class ChangeLogFieldAttribute : Attribute {
        public string FieldName { get; set; }
    }

It's used like this in my model.

    [Display(Name = "Style")]
    [ChangeLogField(FieldName = "styleid")]
    public string Style { get; set; }

In my helper method, I've got the following code to get the FieldName value of my attribute, if the attribute is used for the property.

        var itemName = ((MemberExpression)ex.Body).Member.Name;

        var containerType = html.ViewData.ModelMetadata.ContainerType;
        var attribute = ((ChangeLogFieldAttribute[])containerType.GetProperty(html.ViewData.ModelMetadata.PropertyName).GetCustomAttributes(typeof(ChangeLogFieldAttribute), false)).FirstOrDefault();
        if (attribute != null) {
            itemName = attribute.FieldName;
        }

However, when I reach this code, I get an exception because the containerType is null.

I'm not sure if I'm doing any of this correct, but I pulled from about 4 different sources to get this far. If you could suggest a fix to my problem or an alternative, I'd be grateful.

Thanks.

UPDATE WITH SOLUTION

I used Darin Dimitrov's solution, although I had to tweak it some. Here is what I added. I had to check for the existence of the attribute metatdata and all was good.

        var fieldName = ((MemberExpression)ex.Body).Member.Name;

        var metadata = ModelMetadata.FromLambdaExpression(ex, html.ViewData);
        if (metadata.AdditionalValues.ContainsKey("fieldName")) { 
            fieldName = (string)metadata.AdditionalValues["fieldName"];
        }

解决方案

You could make the attribute metadata aware:

public class ChangeLogFieldAttribute : Attribute, IMetadataAware
{
    public string FieldName { get; set; }

    public void OnMetadataCreated(ModelMetadata metadata)
    {
        metadata.AdditionalValues["fieldName"] = FieldName;
    }
}

and then inside the helper:

var metadata = ModelMetadata.FromLambdaExpression(ex, htmlHelper.ViewData);
var fieldName = metadata.AdditionalValues["fieldName"];

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