serialise bool? error reflecting type

Question

i have a class like

   [Serializable]
    public class MyClass
    {
        [XmlAttribute]
        public bool myBool { get; set; }
    }

But this serializes the value of the bool to false when the attribute is not present in the xml. When the attribute is not in the xml I want the property to be null.

So i tried this

[Serializable]
public class MyClass
{
    [XmlAttribute]
    public bool? myBool { get; set; }
}

But then the serializer errors

Type t = Type.GetType("Assembly.NameSpace.MyClass");
                XmlSerializer mySerializer = new XmlSerializer(t); //error "There was an error reflecting type"

Please give me a example of i can do this. I know there are some related questions on SO but nothing that shows how to overcome the reflection error with a nullable bool. Thanks.

score 10 · Accepted Answer · answered Mar 30 '12 at 12:14

10

You need to use the "*Specified" field pattern to control this (see "Controlling Generated XML" on MSDN):

[Serializable]
public class MyClass
{
    [XmlAttribute]
    public bool myBool { get; set; }

    [XmlIgnore]
    public bool myBoolSpecified;
}

The logic now becomes:

If !myBoolSpecified, then myBool is logically null
Else use the true or false of myBool

answered Mar 30 '12 at 12:14

Jon

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@Aliostad: I appreciate the merits of your approach, but if the XML structure is not open to modification it will not work while this one will. – Jon Mar 30 '12 at 12:18
this looks great but doesnt seem to work. Is the '{}Specified' a magic name? do I need some logic in the getter? – Jules Mar 30 '12 at 12:22
@Jules: Yes, it's a magic name. Search for "The pattern is created in the form of propertyNameSpecified" on the linked page. If it doesn't work please show your current code. – Jon Mar 30 '12 at 12:24
1

I have a problem with this. Whilst it does leave out the attribute when deserialising it doesnt serialise the property to an attribute when the property has a value. I need the solution to work in both directions. – Jules Mar 30 '12 at 14:07
@Jules: I 'm not sure what you mean. What's the value of both the property and the field when you serialize? – Jon Mar 30 '12 at 17:05
I have a real problem with this as well. This is a major in the serializer. So, we can serialize nullable integers, but we can't serialize nullable bools? Madness. – Christian Findlay Jun 07 '18 at 09:26

score 3 · Answer 2 · edited May 23 '17 at 11:45

Have a look at this for information regarding dealing with nullable fields and XML attributes. There is a similar question here too. Basically the serializer cannot handle an XML attribute field defined as nullable, but there is a work-around.

I.e 2 properties, one which contains the nullable (not XML stored), and the other which is used in the read/writing (XML attribute stored as a string). Perhaps this might be what you need?

private bool? _myBool;
[XmlIgnore]
public bool? MyBool
{
    get
    {
        return _myBool;
    }
    set
    {
        _myBool = value;
    }
}

[XmlAttribute("MyBool")]
public string MyBoolstring
{
    get
    {
        return MyBool.HasValue
        ? XmlConvert.ToString(MyBool.Value)
        : string.Empty;
    }
    set
    {
        MyBool =
        !string.IsNullOrEmpty(value)
        ? XmlConvert.ToBoolean(value)
        : (bool?)null;
    }
}

score 2 · Answer 3 · answered Mar 30 '12 at 12:13

The problem is that a nullable type has to be defined as an element (which is default) and not Attribute.

Reason is when the value is null, it can be represented as <mybool xs:nil="true"/> as such cannot be represented as attribute.

Have a look at this snippet:

[Serializable]
public class MyClass
{
    // removed the attribute!!!
    public bool? myBool { get; set; }
}

And:

XmlSerializer serializer = new XmlSerializer(typeof(MyClass));
var stream = new MemoryStream();
serializer.Serialize(stream, new MyClass(){myBool = null});
Console.WriteLine(Encoding.UTF8.GetString(stream.ToArray()));

Output:

<?xml version="1.0"?>
<MyClass xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.o
rg/2001/XMLSchema-instance">
  <myBool xsi:nil="true" /> <!-- NOTE HERE !!! -->
</MyClass>

Thanks, but this is attribute in the xml I receive so I cant control that. Is there any way to have a nullable bool attribute? — Jules, Mar 30 '12 at 12:21

score 1 · Answer 4 · answered Dec 18 '13 at 07:58

1

You can use XmlElementAttribute.IsNullable:

[Serializable]
public class MyClass
{
    [XmlElement(IsNullable = true)]
    public bool? myBool { get; set; }
}

answered Dec 18 '13 at 07:58

Yochai Timmer

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1

That is only workable when you can choose to instead serialise as an element, instead of an attribute – Rowland Shaw May 14 '15 at 15:02

serialise bool? error reflecting type

4 Answers4