c# - 禁止 XmlSerializer 发出空值类型

Question

请考虑以下标记为可为 null 的 XmlElement 的 Amount 值类型属性:

[XmlElement(IsNullable=true)] 
public double? Amount { get ; set ; }

当可空值类型设置为 null 时，C# XmlSerializer 结果如下所示:

<amount xsi:nil="true" />

我希望 XmlSerializer 完全抑制该元素，而不是发出该元素。为什么？我们使用 Authorize.NET 进行在线支付，如果存在此 null 元素，Authorize.NET 将拒绝请求。

当前的解决方案/解决方法是根本不序列化 Amount 值类型属性。相反，我们创建了一个补充属性 SerializableAmount，它基于 Amount 并被序列化。由于 SerializableAmount 是 String 类型，如果默认情况下为 null，它就像引用类型一样被 XmlSerializer 抑制，所以一切都很好。

/// <summary>
/// Gets or sets the amount.
/// </summary>
[XmlIgnore]
public double? Amount { get; set; }

/// <summary>
/// Gets or sets the amount for serialization purposes only.
/// This had to be done because setting value types to null 
/// does not prevent them from being included when a class 
/// is being serialized.  When a nullable value type is set 
/// to null, such as with the Amount property, the result 
/// looks like: &gt;amount xsi:nil="true" /&lt; which will 
/// cause the Authorize.NET to reject the request.  Strings 
/// when set to null will be removed as they are a 
/// reference type.
/// </summary>
[XmlElement("amount", IsNullable = false)]
public string SerializableAmount
{
    get { return this.Amount == null ? null : this.Amount.ToString(); }
    set { this.Amount = Convert.ToDouble(value); }
}

当然，这只是一种解决方法。有没有更简洁的方法来抑制 null 值类型元素被发出？

Answer 1

尝试添加:

public bool ShouldSerializeAmount() {
   return Amount != null;
}

框架的某些部分可以识别多种模式。有关信息，XmlSerializer 还会查找 public bool AmountSpecified {get;set;}。

完整示例(也切换到 decimal):

using System;
using System.Xml.Serialization;

public class Data {
    public decimal? Amount { get; set; }
    public bool ShouldSerializeAmount() {
        return Amount != null;
    }
    static void Main() {
        Data d = new Data();
        XmlSerializer ser = new XmlSerializer(d.GetType());
        ser.Serialize(Console.Out, d);
        Console.WriteLine();
        Console.WriteLine();
        d.Amount = 123.45M;
        ser.Serialize(Console.Out, d);
    }
}

有关 ShouldSerialize* on MSDN 的更多信息.