C# 使用代码默认值对集合属性进行XML反序列化

对于应用程序配置，我经常会创建一个配置类，其中包含应用程序的配置值，然后将其反序列化为要利用的对象。配置对象通常被数据绑定到用户界面控件，以便用户可以更改和持久化配置。配置类通常具有指定给属性的默认值，因此始终存在默认配置。这很有效。我最近遇到了一个情况，我有一个字符串列表，其中提供了一些默认路径信息。我所看到的让我意识到，在XML反序列化到对象的过程中，我并不完全知道对象属性是如何填充的

因此，我创建了一个简单的示例来展示这种行为。下面是一个简单的类，它有几个属性，这些属性具有一些代码默认值

[Serializable]
public class TestConfiguration
   {
      public String Name 
      { 
         get
         {
            return mName;
         }
         set
         {
            mName = value;
         }
      }private String mName = "Pete Sebeck";

  public List<String> Associates 
  { 
     get
     {
        return mAssociates;
     }
     set
     {
        mAssociates = value;
     }
  } private List<String> mAssociates = new List<string>() { "Jon", "Natalie" };

  public override String ToString()
  {
     StringBuilder buffer = new StringBuilder();
     buffer.AppendLine(String.Format("Name: {0}", Name));
     buffer.AppendLine("Associates:");
     foreach(String associate in mAssociates)
     {
        buffer.AppendLine(String.Format("\t{0}", associate));
     }
     return buffer.ToString();
  }
   }

结果:

Name: Pete Sebeck
Associates:
        Jon
        Natalie

Name: Pete Sebeck
Associates:
        Jon
        Natalie
        Jon
        Natalie

---

我想我一直认为应该设置列表属性，而不是附加到列表中。有人有指向集合反序列化过程的指针吗？显然，我现在知道了正确的搜索词，因为我的搜索结果是空的。我看到其他帖子描述了我所看到的以及他们自己实现序列化的方法。我更多的是寻找一个指针来描述当集合被反序列化时会发生什么，这样我就可以向自己解释我看到了什么。

很多序列化程序（虽然不是全部）都是这样工作的，这是正确的。Json.NET确实如此，它的方法实际上有一个

对象existingValue

，正好适合这种情况

我不知道有任何文档详细说明了这些实现细节。确定序列化程序是否在存在时使用预先分配的集合而不是无条件分配然后设置集合的最简单方法是使用

ObservableCollection

并在更改时附加调试侦听器来实际测试它：

[Serializable]
[DataContract]
public class TestConfiguration
{
    [DataMember]
    public String Name { get { return mName; } set { mName = value; } }

    private String mName = "Pete Sebeck";

    [DataMember]
    public ObservableCollection<String> Associates
    {
        get
        {
            Debug.WriteLine(mAssociates == null ? "Associates gotten, null value" : "Associates gotten, count = " + mAssociates.Count.ToString());
            return mAssociates;
        }
        set
        {
            Debug.WriteLine(value == null ? "Associates set to a null value" : "Associates set, count = " + value.Count.ToString());
            RemoveListeners(mAssociates);
            mAssociates = AddListeners(value);
        }
    }

    private ObservableCollection<String> mAssociates = AddListeners(new ObservableCollection<string>() { "Jon", "Natalie" });

    public override String ToString()
    {
        StringBuilder buffer = new StringBuilder();
        buffer.AppendLine(String.Format("Name: {0}", Name));
        buffer.AppendLine("Associates:");
        foreach (String associate in mAssociates)
        {
            buffer.AppendLine(String.Format("\t{0}", associate));
        }
        return buffer.ToString();
    }

    static ObservableCollection<String> AddListeners(ObservableCollection<String> list)
    {
        if (list != null)
        {
            list.CollectionChanged -= list_CollectionChanged; // In case it was already there.
            list.CollectionChanged += list_CollectionChanged;
        }
        return list;
    }

    static ObservableCollection<String> RemoveListeners(ObservableCollection<String> list)
    {
        if (list != null)
        {
            list.CollectionChanged -= list_CollectionChanged; // In case it was already there.
        }
        return list;
    }

    public static ValueWrapper<bool> ShowDebugInformation = new ValueWrapper<bool>(false);

    static void list_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (!ShowDebugInformation)
            return;
        switch (e.Action)
        {
            case NotifyCollectionChangedAction.Add:
                Debug.WriteLine(string.Format("Added {0} items", e.NewItems.Count));
                break;
            case NotifyCollectionChangedAction.Move:
                Debug.WriteLine("Moved items");
                break;
            case NotifyCollectionChangedAction.Remove:
                Debug.WriteLine(string.Format("Removed {0} items", e.OldItems.Count));
                break;
            case NotifyCollectionChangedAction.Replace:
                Debug.WriteLine("Replaced items");
                break;
            case NotifyCollectionChangedAction.Reset:
                Debug.WriteLine("Reset collection");
                break;
        }
    }
}

public static class TestTestConfiguration
{
    public static void Test()
    {
        var test = new TestConfiguration();

        Debug.WriteLine("\nTesting Xmlserializer...");
        var xml = XmlSerializationHelper.GetXml(test);
        using (new SetValue<bool>(TestConfiguration.ShowDebugInformation, true))
        {
            var testFromXml = XmlSerializationHelper.LoadFromXML<TestConfiguration>(xml);
            Debug.WriteLine("XmlSerializer result: " + testFromXml.ToString());
        }

        Debug.WriteLine("\nTesting Json.NET...");
        var json = JsonConvert.SerializeObject(test, Formatting.Indented);
        using (new SetValue<bool>(TestConfiguration.ShowDebugInformation, true))
        {
            var testFromJson = JsonConvert.DeserializeObject<TestConfiguration>(json);
            Debug.WriteLine("Json.NET result: " + testFromJson.ToString());
        }

        Debug.WriteLine("\nTesting DataContractSerializer...");
        var contractXml = DataContractSerializerHelper.GetXml(test);
        using (new SetValue<bool>(TestConfiguration.ShowDebugInformation, true))
        {
            var testFromContractXml = DataContractSerializerHelper.LoadFromXML<TestConfiguration>(contractXml);
            Debug.WriteLine("DataContractSerializer result: " + testFromContractXml.ToString());
        }

        Debug.WriteLine("\nTesting BinaryFormatter...");
        var binary = BinaryFormatterHelper.ToBase64String(test);
        using (new SetValue<bool>(TestConfiguration.ShowDebugInformation, true))
        {
            var testFromBinary = BinaryFormatterHelper.FromBase64String<TestConfiguration>(binary);
            Debug.WriteLine("BinaryFormatter result: " + testFromBinary.ToString());
        }

        Debug.WriteLine("\nTesting JavaScriptSerializer...");
        var javaScript = new JavaScriptSerializer().Serialize(test);
        using (new SetValue<bool>(TestConfiguration.ShowDebugInformation, true))
        {
            var testFromJavaScript = new JavaScriptSerializer().Deserialize<TestConfiguration>(javaScript);
            Debug.WriteLine("JavaScriptSerializer result: " + testFromJavaScript.ToString());
        }
    }
}

现在集合返回时只包含以前序列化的成员和所有5个序列化器

[Serializable]
[DataContract]
public class TestConfiguration
{
    [DataMember]
    public String Name { get { return mName; } set { mName = value; } }

    private String mName = "Pete Sebeck";

    [DataMember]
    public ObservableCollection<String> Associates
    {
        get
        {
            Debug.WriteLine(mAssociates == null ? "Associates gotten, null value" : "Associates gotten, count = " + mAssociates.Count.ToString());
            return mAssociates;
        }
        set
        {
            Debug.WriteLine(value == null ? "Associates set to a null value" : "Associates set, count = " + value.Count.ToString());
            RemoveListeners(mAssociates);
            mAssociates = AddListeners(value);
        }
    }

    private ObservableCollection<String> mAssociates = AddListeners(new ObservableCollection<string>() { "Jon", "Natalie" });

    public override String ToString()
    {
        StringBuilder buffer = new StringBuilder();
        buffer.AppendLine(String.Format("Name: {0}", Name));
        buffer.AppendLine("Associates:");
        foreach (String associate in mAssociates)
        {
            buffer.AppendLine(String.Format("\t{0}", associate));
        }
        return buffer.ToString();
    }

    static ObservableCollection<String> AddListeners(ObservableCollection<String> list)
    {
        if (list != null)
        {
            list.CollectionChanged -= list_CollectionChanged; // In case it was already there.
            list.CollectionChanged += list_CollectionChanged;
        }
        return list;
    }

    static ObservableCollection<String> RemoveListeners(ObservableCollection<String> list)
    {
        if (list != null)
        {
            list.CollectionChanged -= list_CollectionChanged; // In case it was already there.
        }
        return list;
    }

    public static ValueWrapper<bool> ShowDebugInformation = new ValueWrapper<bool>(false);

    static void list_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (!ShowDebugInformation)
            return;
        switch (e.Action)
        {
            case NotifyCollectionChangedAction.Add:
                Debug.WriteLine(string.Format("Added {0} items", e.NewItems.Count));
                break;
            case NotifyCollectionChangedAction.Move:
                Debug.WriteLine("Moved items");
                break;
            case NotifyCollectionChangedAction.Remove:
                Debug.WriteLine(string.Format("Removed {0} items", e.OldItems.Count));
                break;
            case NotifyCollectionChangedAction.Replace:
                Debug.WriteLine("Replaced items");
                break;
            case NotifyCollectionChangedAction.Reset:
                Debug.WriteLine("Reset collection");
                break;
        }
    }
}

public static class TestTestConfiguration
{
    public static void Test()
    {
        var test = new TestConfiguration();

        Debug.WriteLine("\nTesting Xmlserializer...");
        var xml = XmlSerializationHelper.GetXml(test);
        using (new SetValue<bool>(TestConfiguration.ShowDebugInformation, true))
        {
            var testFromXml = XmlSerializationHelper.LoadFromXML<TestConfiguration>(xml);
            Debug.WriteLine("XmlSerializer result: " + testFromXml.ToString());
        }

        Debug.WriteLine("\nTesting Json.NET...");
        var json = JsonConvert.SerializeObject(test, Formatting.Indented);
        using (new SetValue<bool>(TestConfiguration.ShowDebugInformation, true))
        {
            var testFromJson = JsonConvert.DeserializeObject<TestConfiguration>(json);
            Debug.WriteLine("Json.NET result: " + testFromJson.ToString());
        }

        Debug.WriteLine("\nTesting DataContractSerializer...");
        var contractXml = DataContractSerializerHelper.GetXml(test);
        using (new SetValue<bool>(TestConfiguration.ShowDebugInformation, true))
        {
            var testFromContractXml = DataContractSerializerHelper.LoadFromXML<TestConfiguration>(contractXml);
            Debug.WriteLine("DataContractSerializer result: " + testFromContractXml.ToString());
        }

        Debug.WriteLine("\nTesting BinaryFormatter...");
        var binary = BinaryFormatterHelper.ToBase64String(test);
        using (new SetValue<bool>(TestConfiguration.ShowDebugInformation, true))
        {
            var testFromBinary = BinaryFormatterHelper.FromBase64String<TestConfiguration>(binary);
            Debug.WriteLine("BinaryFormatter result: " + testFromBinary.ToString());
        }

        Debug.WriteLine("\nTesting JavaScriptSerializer...");
        var javaScript = new JavaScriptSerializer().Serialize(test);
        using (new SetValue<bool>(TestConfiguration.ShowDebugInformation, true))
        {
            var testFromJavaScript = new JavaScriptSerializer().Deserialize<TestConfiguration>(javaScript);
            Debug.WriteLine("JavaScriptSerializer result: " + testFromJavaScript.ToString());
        }
    }
}

    [IgnoreDataMember]
    [XmlIgnore]
    [ScriptIgnore]
    public ObservableCollection<String> { get; set; } // Or List<string> or etc.

    [XmlArray("Associates")]
    [DataMember(Name="Associates")]
    public string[] AssociateArray
    {
        get
        {
            return (Associates == null ? null : Associates.ToArray());
        }
        set
        {
            if (Associates == null)
                Associates = new ObservableCollection<string>();
            Associates.Clear();
            if (value != null)
                foreach (var item in value)
                    Associates.Add(item);
        }
    }