NonSerialized on property

Question

When I write code like this

[XmlIgnore]
[NonSerialized]
public List<string> paramFiles { get; set; }

I get the following error:

Attribute 'NonSerialized' is not valid on this declaration type.
It is only valid on 'field' declarations.

If I write

[field: NonSerialized]

I get the following warning

'field' is not a valid attribute location for this declaration.
Valid attribute locations for this declaration are 'property'.
All attributes in this block will be ignored.

If I write

[property: NonSerialized]

I get the following error (again):

Attribute 'NonSerialized' is not valid on this declaration type.
It is only valid on 'field' declarations.

How can I use [NonSerialized] on a property?

Anton Norko · Answer 1 · 2012-12-14T08:35:42.000

80

Simple use:

[XmlIgnore]
[ScriptIgnore]
public List<string> paramFiles { get; set; }

Hopefully, it helps.

edited Dec 14 '12 at 08:35

answered May 28 '12 at 21:14

Anton Norko

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Indeed this even works in classic ASP.NET Web Service scenario by completely hiding the property name from the consumer (a great trick for those stuck in pre-WCF project) – timmi4sa Nov 20 '12 at 17:23
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I did not need to use [ScriptIgnore] to make this work – Antonio Nicolaas Teyken Mar 06 '18 at 09:41
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@AntonioNicolaasTeyken It depends on what you're using to serialize the data. In my case, [ScriptIgnore] prevented Json serialization. – General Grievance Jul 25 '19 at 16:03
One more note: `ScriptIgnoreAttribute` is available in the `System.Web.Script.Serialization` namespace ([MSDN](https://learn.microsoft.com/en-us/dotnet/api/system.web.script.serialization.scriptignoreattribute?redirectedfrom=MSDN&view=netframework-4.8)). – Mass Dot Net Sep 19 '19 at 15:42
Just to be clear, this works for binary serializer? Because the question already has XmlIgnore in the example so not sure how this can help. – Corey Alix Feb 27 '20 at 15:29

score 58 · Accepted Answer · edited Oct 30 '18 at 12:03

58

Well... the first error says that you can't do that... from http://msdn.microsoft.com/en-us/library/system.nonserializedattribute.aspx

 [AttributeUsageAttribute(AttributeTargets.Field, Inherited = false)]
 [ComVisibleAttribute(true)]
 public sealed class NonSerializedAttribute : Attribute

I suggest using backing field

 public List<string> paramFiles { get { return list;}  set { list = value; } }
 [NonSerialized]
 private List<string> list;

edited Oct 30 '18 at 12:03

Matze

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answered Oct 07 '11 at 22:21

wiero

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Using the suggested backing field does not seem to work. The property is still being serialized. – Ramon Zarazua B. Oct 23 '12 at 07:35
Yes it works, but not in every class named AaaSerializer. Which serializer are you using? – wiero Oct 23 '12 at 09:16
4

The correct attribute is [NonSerialized], not [NonSerializable] – Setyo N Jun 10 '13 at 10:15
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oy...what if your "backing field" is a method? – drzaus Feb 23 '15 at 19:27
Which serializer do you use? – wiero Aug 11 '15 at 07:08
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NonSerialized will work for BinaryFormatter (at least) which serializes fields, and probably won't work for Json or XML serializers which serialize properties. – Kind Contributor Aug 17 '15 at 05:38

score 50 · Answer 3 · answered Oct 22 '19 at 23:42

50

From C# 7.3 you may attach attributes to the backing field of auto-implemented properties.

Hence the following should work if you update your project's language to C# 7.3:

[field: NonSerialized]
public List<string> paramFiles { get; set; }

answered Oct 22 '19 at 23:42

Bfed

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This should be re-marked as the best answer, because it's pretty awesome. – Min Feb 16 '20 at 06:59
When I use this the property is still serialized with XmlSerializer – Matthew Eskolin Dec 14 '22 at 20:23

score 14 · Answer 4 · answered Oct 28 '19 at 15:36

14

For those using JSON instead of XML you can use the [JsonIgnore] attribute on properties:

[JsonIgnore]
public List<string> paramFiles { get; set; }

Available in both Newtonsoft.Json and System.Text.Json (.NET Core 3.0).

answered Oct 28 '19 at 15:36

Ziad Akiki

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Please note, which package that is doing serialisation matters! If you're doing serialisation with Newtonsoft, don't use the `JsonIgnore` from System.Text.Json (or vice versa). – Andres Sepulveda Jun 14 '23 at 01:01

score 6 · Answer 5 · answered Mar 05 '19 at 18:18

As of .NET 3.0, you can use DataContract instead of Serializable. With the DataContract though, you will need to either "opt-in" by marking the serializable fields with the DataMember attribute; or "opt-out" using the IgnoreDataMember.

The main difference between opt-in vs opt-out is that opt-out by default will only serialize public members, while opt-in will only serialize the marked members (regardless of protection level).

NonSerialized on property

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