This cannot be done in C#. Any way to do it?
...
laugh, in case my little pun wasn't understood, what I mean is: how can I mark a property in C# as NonSerialized? Of course, when the property contains logic, it's natural to be unable to do it, but Auto-Properties are serializable, and, as such, I would expect to have some way to allow me to prevent their serialization.
[NonSerialized]
public string MyProperty { get; set; }
Is an error
[XmlIgnore]
public string MyProperty { get; set; }
Is not an error
NonSerialized Indicates that a field of a serializable class should not be serialized.
XmlIgnore Instructs the Serialize method of the XmlSerializer not to serialize the public field or public read/write property value
so, if you ask
I would expect to have some way to allow me to prevent their serialization.
the answer yes, if you're using XmlSerializer
For events, you can use [field:NonSerialized], but for auto-properties this does not work. It seems like it would be a very logical way to handle auto-properties as well, but for some reason it doesn't seem to have been implemented.
Edit * :
Auto Implemented Properties are backed by an anonymous field which you don't really have access to, attributes are designed to be controlled by a reflection based mechanism. These fields cannot be referenced by the reflection mechanism (because they are anonymous). This compiler feature would require a lot of changes to the generation of auto-properties... It would also require that the compiler treat auto-properties as fields for the purpose of marking field attributes onto them.
To answer the more fundamental part of the question - your point was that Auto-Properties are serialized and so there should be a way to control their serialization. You're right - but auto properties are meant as a shorthand and were never designed to give you the full flexibility, but rather to allow you to easily extend their functionality the "long" way if you ever needed it.
I added the more details answer from my comments to the body of the answer.
I theory yes, it's possible. In practical nope, not possible.
Serialization classes only works on private fields. When you define a auto property; at behind the scenes compiler automatically generates a private field for it. That means this is a language feature not a .net framework feature.
Also serialization classes are included in redbits, which is any change prohibited due compatibility except bug fixes.
I hope thats helps.
What was said above is right: You can't prevent an auto-implemented property from being serialized by setting an attribute like [NonSerialized]. It just does not work.
But what does work is the [IgnoreDataMember] attribute in case you are working with an WCF [DataContract]. So
[DataContract]
public class MyClass
{
[DataMember]
public string ID { get; set; }
[IgnoreDataMember]
public string MySecret { get; set; }
}
will get serialized under WCF.
Although since WCF is an opt-in technology, you can also just omit the [IgnoreDataMember] and it will work as well. So maybe my comment is a little academical ;-)
You could probably do this with Mono.Cecil, a bytecode manipulation library. Theoretically, you could add custom attributes to the hidden backing field. This is so inconvenient, however, that I don't think it warrants an example.
If you had a large application with your own postprocessor, you might consider creating your own substitute for NonSerializedAttribute that could be applied to properties. The postprocessor could then use Mono.Cecil or similar to apply NonSerializedAttribute to the backing fields. It's quite common for large applications to undergo such postprocessing to save that extra bit of typing.
[NonSerialized] public decimal yourproperty;
(decimal as example.)
Also remember, if you want enable your class to initialize a nonserialized member automatically, use the IDeserializationCallback interface and then implement IDeserializationCallback.OnDeserialization.
Related
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
C#: Public Fields versus Automatic Properties
Do I need to use { get; set; } with c# fields that have no special actions when getting and setting
Consider these two options:
public int Foo { get; set; }
public int Foo;
They seem to be semantically equivalent, and I believe they will even compile to the same IL. So what is the advantage of using the property? Seeing a public field makes me feel uneasy, but I can't think of any concrete advantage to using the property syntax instead. If an explicit getter and setter are required in the future, public int Foo; can be replaced by public int Foo { ... } with no other changes necessary. The best I can come up with is that the property syntax just feels better, but I can hardly use this reason to convince someone else.
What is the advantage (if any) of using the property syntax in this case?
The main advantages are:
Future-proofing your API - If you later need logic in the getter or setter, your public API doesn't change.
Data binding - Most data binding frameworks only work against Properties, not Fields.
Pros
Easy declaration
Cons
Can not set a breakpoint inside set/get
Can not have a code inside get/set
Do not working on WPF DataBinding
No concept like a default value for the property, as there is no default field behind it.
Pros and cons are strictly related to the project implementation.
Just a couple of hints, pretty sure others will add something else...
I do not believe they will compile to the same IL, as get and set for properties are actually functions on the IL level and when dealing with reflection. Here are some reasons to do it though:
Reflection!
Serialization/Deserialization only works on public properties, not public fields.
Debugging, you can set break points on a get or a set, which can help to track down when the variable is accessed, specifically if you are seeing a goofy value and you don't know where it is coming from.
The primary reason that we don't use auto-implemented properties is for those serialization mechanisms that serialize the members and not the properties (such as binary serialization for .Net remoting).
In this case, if you have two applications that compile the same class separately and exchange a serialized copy of the class, there is no guarantee that it will deserialize correctly since you can't control the names of the private members.
I find the [DataContract] and [DataMember] attributes a bit messy and would rather do this with code in a config method or something. Is this possible?
You don't have to use these attributes at all. DataContractSerializer will serialize all public properties with getter and setter but in case of serializing entities with navigation properties you will easily end with exception due to "cyclic reference".
To avoid that exception you must either use [DataContract(IsReference = true)] on your entity class with DataMember on every property you want to serilize or IgnoreDataMember on every property you don't want to serialize.
The last and the most complex option is avoiding attributes completely and custom classes implementing IDataContractSurrogate to control serialization outside of the type.
You can also write your completely custom serialization process or use XML serialization or binary serialization with all its requirements.
No, the DataContractSerializer is an opt-in serializer - you have to tell it what you want included.
With other serializers you need to use things like NonSerializedAttribute or XmlIgnoreAttribute to tell the serializer to leave things alone.
I know this is a rather old post, but I came here thinking the same thing if there is a way to set all member attributes automatically on some legacy code with public fields and no getters and setters.
What makes it look just a little bit less messy is shortening up the name DataMember:
using DM = System.Runtime.Serialization.DataMemberAttribute;
[DataContract]
public class SomeClass
{
[DM] public bool IsMO;
[DM] public string LabCode;
[DM] public string OrderNumber;
}
So I've been studying the use of various Serializers in the .NET Framework and while trying to experiment on preventing certain objects in a class from being serialized I was thrusted back to some very basic programming questions that I "thought" I knew. Given this example:
public class Example
{
public string examName;
[XmlIgnore]
public int exampleNumber;
public Example()
{ }
[XmlIgnore]
public int ExampleNumberTwo { get; set; }
}
I can create an instance of this class and using the XMLSerializer can output the content of this class in XML format. The [XmlIgnore] attribute actually does what I'd expected; it prevents the serialization of the referenced items.
So venturing further I replaced the [XmlIgnore] declaration for "exampleNumber" with [NonSerializable] expecting the similar results but the output did not change. After searching through resources, it was stated that the [NonSerializable] attribute should only be used on fields and [XmlIgnore] attributes should be used on properties.
Yet another post stated that the [NonSerializable] attribute has no effect when using the XMLSerializer but will produce the expected results when using the SOAP or BinaryFormatter. So I'm lost on the concept at this point.
But this brought me to the basic question, what defines a field vs. a property? I know its a basic question and I've even viewed other discussions here but the degree of clarity I am looking for still wasn't really clear.
I can use the [XmlIgnore] attribute on the property (ExampleNumberTwo) or the variable (exampleNumber) so the statement that it can ONLY be used on Properties doesn't seem correct.
But then again, I have always referred to the objects in my example such as (examName) and (exampleNumber) as being member variables. So what exactly is the signature of a "Field"
Can anyone shed some light on this?
The MSDN documentation supports the idea that [NonSerialized] only gives the expected results with the binary and SOAP serializers:
When using the BinaryFormatter or SoapFormatter classes to serialize
an object, use the NonSerializedAttribute attribute to prevent a field
from being serialized. For example, you can use this attribute to
prevent the serialization of sensitive data.
The target objects for the NonSerializedAttribute attribute are public
and private fields of a serializable class. By default, classes are
not serializable unless they are marked with SerializableAttribute.
During the serialization process all the public and private fields of
a class are serialized by default. Fields marked with
NonSerializedAttribute are excluded during serialization. If you are
using the XmlSerializer class to serialize an object, use the
XmlIgnoreAttribute class to get the same functionality. Alternatively,
implement the ISerializable interface to explicitly control the
serialization process. Note that classes that implement ISerializable
must still be marked with SerializableAttribute.
In terms of "field" vs. "property", fields are straight data variables contained by a class. Properties are actually specially named methods on the class (get_PropName() and set_PropName()). In your code, the compiler allows you to use properties the same way you would use a field, and then inserts the appropriate get/set call for you.
Oftentimes, properties will be simple wrappers around a field:
private int myField;
public int MyProperty
{
get { return myField; }
set { myField = value; }
}
But they don't have to be:
public int TodaysDate
{
get { return DateTime.Today; }
}
In general, you want all your fields to be private, since they're supposed to be implementation details. Any simple data that you'd like to expose should be done via a property, since you can easily surround the data access with (changeable) logic.
In C#, the short answer is that properties have get and/or set methods, while fields do not. VB.NET makes it a little more evident by requiring the "Property" qualifier to be used to differentiate one.
With C#, you can just append " { get; set; }" to the end of a field's definition and it's now a property.
Where this really comes into play is in reflection. Fields and Properties are segregated from one another into different enumerable collections.
This answer to What are the differences between the XmlSerializer and BinaryFormatter will help you get started in the right direction.
This question already has answers here:
Closed 12 years ago.
Possible Duplicates:
c#: why have empty get set properties instead of using a public member variable?
C#: Public Fields versus Automatic Properties
I am using "automatic" properties in my code,
and I wonder what is the actual difference between
this code:
public class foo{
public int i;
}
and
public class foo{
public int i {get; set;}
}
I know there is a difference, as sine 3rd parties that I've used missed the public members but found them once adding the {get; set;}.
AS there is no private field behind that, what is going behind the scene ?
A private field gets generated by the compiler when using automatic properties.
When you declare a property as shown in the following example, the compiler creates a private, anonymous backing field that can only be accessed through the property's get and set accessors.
In regards to the difference between the two examples - the first one exposes the field directly for manipulation. This is considered bad practice (think information hiding, loss of encapsulation).
With the second example, you must use the getter and setter and you can add any kind of validation and other logic around these actions.
See this blog post:
If I have a field with no special behavior, should I write a "just in case" property (with trivial get/set), or should I expose a public field?
The reason that the library design guidelines suggest you write a property here is that it is important that libraries be easily versioned. If you put a property in there ahead of time, you can change the property implementation without requiring users to recompile their code.
The first is a field and could be described as POD. The second is a property and allow for derived classes to overload and Shadow while the first does not. Also the second is a nicety since the complier silently creates a backing store.
That's an auto property, not an anonymous property. There is, in fact, a private backing field for it, it's just generated automatically by the compiler and isn't available to you at compile time. If you run your class through something like Reflector (or examine it at runtime with reflection), you'll see the backing field.
To answer your question of "What's the difference?", the obvious answer is that one is a field, whereas one is a property. The advantage to using auto properties is that it gives you the flexibility to move to traditional properties later, should the need arise, without changing your API. As far as third party code being able to "reach" one but not the other, that would be a question best answered by the other developer. That being said, most API's are designed to work on properties, not fields (since conventional wisdom is that you do not expose fields outside of the declaring class). If the third-party library is reflectively scanning your class, then it's likely only looking for properties.
The important thing to remember is that:
private string backingField;
public string Data
{
get { return backingField; }
set { backingField = value; }
}
and
public string Data { get; set; }
Are compiled to essentially the same code. The only substantive difference is the name of the backing field.
I'm looking through some existing code in a project I'm working on, and I found a class that is implemented as:
public class ThingOne
{
private int A;
private int B;
[NonSerialized]
private System.Timers.Timer timer1;
}
Shouldn't it look more like this?
[Serializable]
public class ThingOne
{
private int A;
private int B;
[NonSerialized]
private System.Timers.Timer timer1;
}
Or is there some additional benefit to adding [NonSerialized] even when the class itself is not Serializable?
Or is there some additional benefit to adding [NonSerialized] even when the class itself is not Serializable?
The class isn't sealed, so another class could inherit from that object. That class could be marked as Serializable, and then the NotSerializable attribute would come into play. (although as pointed out not for private members).
Remember you can check attributes by reflection too. It may not be used by the runtime to check what should and should not be serialized, it could be used as a marker for something else in the program dealing with some sort of custom serialization (I'm not saying this is a good idea in the least).
NonSerialized will have no effect when Serializable is not used. By default, classes and their members are non-serializable.
The only advantage of declaring something NonSerialized when the class isn't serialized is under the circumstances that the class is inherited by a Serialized object, and then the inherited member will be non-serializable.
From MSDN:
'NonSerialized' attribute will not
affect this member because its
containing class is not exposed as
'Serializable'.
By default, classes and their members are non-serializable. The NonSerializedAttribute attribute is only needed if a member of a serializable class should not be serialized.
I can think of two reasons:
It could be vital that the field isn't serialised. Hence if in the future the class is made serialisable, this won't introduce a bug, inefficiency or security issue, because without it marking the class serialisable will also do so for the field.
They could be doing some sort of custom use of the attribute
In case 2 it'll be clear from elsewhere in the code that this is what's happening. Number 1 is good practice though.
Case 1 is good practice, it can be worth balancing YAGNI ("You Aren't Gonna Need It" - not doing work "in case it's needed later") with considering "okay, but if I do need it later, it'll be a disaster if someone misses that this field is an exception.
So, while it has no effect here, it is definitely a good practice for scenarios where it begins to have an effect.
Edit: Another possibility is that it is cruft from a previous version where it was indeed serialisable or the author was in two minds at the time and it was never entirely "finished" (is working code ever entirely finished?). Just because something is in code, doesn't mean it was meant to be that way. Still, if it's really important that something not be serialised, I still say it's good practice to mark this for the reason given above.
MSDN SerializeAttribute states that "Apply the SerializableAttribute attribute to a type to indicate that instances of this type can be serialized. " This implies that without it, the class cannot be serialized. I believe I have attempted this and the serialize will throw an exception if it is attempted on a NonSerializable Type.
I agree with Greg, MSDN states it in a similar manner, citing references is a good idea..
"By default, classes and their members are non-serializable. The NonSerializedAttribute attribute is only needed if a member of a serializable class should not be serialized."
http://msdn.microsoft.com/en-us/library/dwys85sk(VS.80).aspx