我对ConfigurationProperty的DefaultValue有一个小问题。
以下是我的XML配置的一部分:
<Storage id="storageId">
<Type>UNC</Type>
</Storage>
要处理此配置,我创建了“StorageElement:ConfigurationElement”:
public class StorageElement : ConfigurationElement
{
private static readonly ConfigurationPropertyCollection PropertyCollection = new ConfigurationPropertyCollection();
internal const string IdPropertyName = "id";
internal const string TypePropertyName = "Type";
public StorageElement()
{
PropertyCollection.Add(
new ConfigurationProperty(
IdPropertyName,
typeof(string),
"",
ConfigurationPropertyOptions.IsRequired | ConfigurationPropertyOptions.IsKey
));
PropertyCollection.Add(
new ConfigurationProperty(
TypePropertyName,
typeof(ConfigurationTextElement<string>),
null,
ConfigurationPropertyOptions.IsRequired));
}
public string Id
{
get
{
return base[IdPropertyName] as string;
}
}
public string Type
{
get
{
return (base[TypePropertyName] as ConfigurationTextElement<string>).Value;
}
}
public override bool IsReadOnly()
{
return true;
}
protected override ConfigurationPropertyCollection Properties
{
get { return PropertyCollection; }
}
}
对于Type属性,我正在使用ConfigurationTextElement:
public class ConfigurationTextElement<T> : ConfigurationElement
{
public override bool IsReadOnly()
{
return true;
}
private T _value;
protected override void DeserializeElement(XmlReader reader, bool serializeCollectionKey)
{
_value = (T)reader.ReadElementContentAs(typeof(T), null);
}
public T Value
{
get { return _value; }
set { _value = value; }
}
}
问题是我无法为我的Type-property设置not-null DefaultValue。错误是:
An error occurred creating the configuration section handler for xxxConfigurationSection:
Object reference not set to an instance of an object.
我需要添加什么来启用默认值?
答案 0 :(得分:4)
添加以下属性并检查是否为空。
[ConfigurationProperty("Type", DefaultValue="something")]
public string Type
{
get
{
var tmp = base[TypePropertyName] as ConfigurationTextElement<string>;
return tmp != null ? tmp.Value : "something";
}
}