具有 XmlArrayItemAttribute 的多个实例的 GetCustomAttribute

发布于 2024-11-16 01:30:21 字数 1336 浏览 5 评论 0原文

我有一个 List。TransformationItem 只是多个类的基类，例如 ExtractTextTransform 和 InsertTextTransform

为了使用内置的 XML 序列化和反序列化，我必须使用 XmlArrayItemAttribute 的多个实例，如 http://msdn.microsoft .com/en-us/library/system.xml.serialization.xmlarrayitemattribute%28v=vs.80%29.aspx

您可以应用 XmlArrayItemAttribute 或 XmlElementAttribute 的多个实例来指定可插入数组中的对象类型。

这是我的代码：

[XmlArrayItem(Type = typeof(Transformations.EvaluateExpressionTransform))]
[XmlArrayItem(Type = typeof(Transformations.ExtractTextTransform))]
[XmlArrayItem(Type = typeof(Transformations.InsertTextTransform))]
[XmlArrayItem(Type = typeof(Transformations.MapTextTransform))]
[XmlArrayItem(Type = typeof(Transformations.ReplaceTextTransform))]
[XmlArrayItem(Type = typeof(Transformations.TextItem))]
[XmlArrayItem(ElementName = "Transformation")]
public List<Transformations.TransformationItem> transformations;

问题是，当我使用反射通过 GetCustomAttribute() 获取 ElementName 属性时，我得到了 AmbigouslyMatchException。

我该如何解决这个问题，比如说获取 ElementName？

原文

I have a List<TransformationItem>.TransformationItem is just base class for multiple classes, such as ExtractTextTransform and InsertTextTransform

In order to use built-in XML Serialization and Deserialization, I have to use multiple instance of XmlArrayItemAttribute, as described in http://msdn.microsoft.com/en-us/library/system.xml.serialization.xmlarrayitemattribute%28v=vs.80%29.aspx

You can apply multiple instances of the XmlArrayItemAttribute or XmlElementAttribute to specify types of objects that can be inserted into the array.

Here is my code:

[XmlArrayItem(Type = typeof(Transformations.EvaluateExpressionTransform))]
[XmlArrayItem(Type = typeof(Transformations.ExtractTextTransform))]
[XmlArrayItem(Type = typeof(Transformations.InsertTextTransform))]
[XmlArrayItem(Type = typeof(Transformations.MapTextTransform))]
[XmlArrayItem(Type = typeof(Transformations.ReplaceTextTransform))]
[XmlArrayItem(Type = typeof(Transformations.TextItem))]
[XmlArrayItem(ElementName = "Transformation")]
public List<Transformations.TransformationItem> transformations;

The problem is, when I use reflection to get ElementName attribute with GetCustomAttribute(), I got AmbiguousMatchException.

How can I solve this, say, get the ElementName?

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野却迷人 2024-11-23 01:30:21

由于找到了多个属性，您需要使用 ICustomAttributeProvider.GetCustomAttributes()。否则，Attribute.GetCustomAttribute() 方法会抛出 AmbigouslyMatchException，因为它不知道要选择哪个属性。

我喜欢将其包装为扩展方法，例如：

public static IEnumerable<TAttribute> GetAttributes<TAttribute>(this ICustomAttributeProvider provider, bool inherit = false)
    where TAttribute : Attribute
{
    return provider
        .GetCustomAttributes(typeof(TAttribute), inherit)
        .Cast<TAttribute>();
}

调用方式如下：

var attribute = typeof(TransformationItem)
    .GetAttributes<XmlArrayItemAttribute>(true)
    .Where(attr => !string.IsNullOrEmpty(attr.ElementName))
    .FirstOrDefault();

if (attribute != null)
{
    string elementName = attribute.ElementName;
    // Do stuff...
}

As more than one attribute was found, you need to use ICustomAttributeProvider.GetCustomAttributes(). Otherwise, the Attribute.GetCustomAttribute() method throws an AmbiguousMatchException, as it doesn't know which attribute to select.

I like to wrap this as an extension method, e.g.:

public static IEnumerable<TAttribute> GetAttributes<TAttribute>(this ICustomAttributeProvider provider, bool inherit = false)
    where TAttribute : Attribute
{
    return provider
        .GetCustomAttributes(typeof(TAttribute), inherit)
        .Cast<TAttribute>();
}

Called like:

var attribute = typeof(TransformationItem)
    .GetAttributes<XmlArrayItemAttribute>(true)
    .Where(attr => !string.IsNullOrEmpty(attr.ElementName))
    .FirstOrDefault();

if (attribute != null)
{
    string elementName = attribute.ElementName;
    // Do stuff...
}

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