I'm having this wierd problem... in my code whether I set the value of IsRequired to false or true then it stays false.. However if I put in a DefaultValue it works?
The non-working code is:
public class FtpSettingsSection : ConfigurationSection
{
[ConfigurationProperty("host", IsRequired = true)]
public HostElement Host
{
get { return (HostElement)this["host"]; }
set { this["host"] = value; }
}
}
public class HostElement : ConfigurationElement
{
[ConfigurationProperty("URL", IsRequired = true)]
public string URL
{
get { return (string)this["URL"]; }
set { this["URL"] = value; }
}
}
and the working code is:
public class FtpSettingsSection : ConfigurationSection
{
[ConfigurationProperty("host", DefaultValue = "", IsRequired = true)]
public HostElement Host
{
get { return (HostElement)this["host"]; }
set { this["host"] = value; }
}
}
public class HostElement : ConfigurationElement
{
[ConfigurationProperty("URL", DefaultValue = "", IsRequired = true)]
public string URL
{
get { return (string)this["URL"]; }
set { this["URL"] = value; }
}
}
How come that I need to set DefaultValue to ""?
I have encountered the same problem and found the solution here http://msdn.microsoft.com/en-us/library/system.configuration.configurationpropertyattribute%28v=vs.90%29.aspx#1. The comment on ConfigurationPropertyAttribute isn't completely correct, but it explains the basics of the problem:
The IsRequired member of ConfigurationPropertyAttribute does not work when applied to a child object (deriving from ConfigurationElement). When the subsystem reflects over the attributes of the parent section/element to determine which configuration properties are defined it will create a new instance (of the appropriate type) for each child element and store it in the parent's value list. Later, when it validates whether all required properties have been specified or not, it cannot differentiate between a default initialized child element and one that was explicitly contained in the configuration file.
The most ideal workaround would be to programmatically declare the required elements through the ConfigurationProperty class. This requires substantial more work than the declarative approach. An alternative...
As far as I can tell the alternative is incorrect.
An example of the programmatic model can be found on the ConfigurationProperty page. I have managed to fix the problem for myself by declaring the properties I need required in the constructor of my custom element and leaving everything else the same.
I suspect for you it is not actually working when you add DefaultValue, but rather throwing an exception for a different reason. You will have to drill down to the end of the InnerException chain to find the ConfigurationErrorsException. The correct message when a required property is missing is "Required attribute 'host' not found. (C:\path\to\yourproject\bin\Debug\yourproject.vshost.exe.Config line ##)"
When you provide an empty string default value the configuration subsystem will try to parse that string into a HostElement and fail. The resulting ConfigurationErrorsException has the message "The default value of the property 'host' cannot be parsed. The error is: Object reference not set to an instance of an object. (C:\path\to\yourproject\bin\Debug\yourproject.vshost.exe.Config line ##)"
Digging up a dead thread.
But I accidentally found a work around for this.
In your custom section constructor, make a reference to a custom element's ElementInformation. By doing that, another instance of your custom section will created in the element's context. And for some reason that I don't understand fully, the IsRequired property is honored.
public class FtpSettingsSection : ConfigurationSection
{
public FtpSettingsSection()
{
// force it to double load.
if (this.Host.ElementInformation.IsPresent) ;
}
[ConfigurationProperty("host", IsRequired = true)]
public HostElement Host
{
get { return (HostElement)this["host"]; }
set { this["host"] = value; }
}
}
Sorry for necroposting, but this problem hit me too but in a more peculiar way and my solution also applies to the question asked.
I implemented reloading a config without restarting a process.
When the process starts, the IsRequired attribute is "ignored" and the ConfigurationElement is silently initialized with default values. But when the config is reloaded, the IsRequired attributed is respected! So I hardcoded reloading configuration on process start and it solved the problem of missing exception!
Pseudocode:
config = (SampleConfiguration)ConfigurationManager.GetSection(ConfigSectionName);
// <-- no exception thrown for missing required properties
ConfigurationManager.RefreshSection(ConfigSectionName);
config = (SampleConfiguration)ConfigurationManager.GetSection(ConfigSectionName);
// <-- exception thrown!
I am assuming you dont have the URL propertie's value serialized in your configuration. So when the configuration is being loaded the ConfigurationManager checks the attributes to see if the property value required and then throws exception if finds no value. If default value is set, then that value is used if none found in the config.
Related
Researched this error and some have said it's a bug but when I used some of their suggestions it didn't fix the problem. What should I do?
**Code
/// Indicates if the profiles has been added.
public Boolean _isNew
{
get { return _isNew; }
set { _isNew = value; }
}
/// Indicates if any of the fields in the class have been modified
public Boolean _isDirty
{
get { return _isDirty; }
set { _isDirty = value; }
}
//Gets and Sets delimiterChar
public Char _delimiterChar
{
get { return _delimiterChar; }
set { _delimiterChar = value;}
}
Error**
Ambiguity between 'ConsoleApplication3.ProfileClass.isNew'and 'ConsoleApplication3.ProfileClass.isNew
Ambiguity between 'ConsoleApplication3.ProfileClass.isDirty'and 'ConsoleApplication3.ProfileClass.isDirty
Ambiguity between 'ConsoleApplication3.ProfileClass._delimiterChar'and 'ConsoleApplication3.ProfileClass._delimiterChar
The code you have posted will cause recursion and eventual stackoverflow. You're trying to set property inside the property setter. You either need a backing field or automatic properties to achieve what you're doing. Something like:
private bool _isNew;
public Boolean IsNew
{
get { return _isNew; }
set { _isNew = value; }
}
or
public Boolean IsNew {get; set;}
In C#, if you specify what you are getting and setting, you cannot use the same name as the property (self-reference issue). As of now, you are attempting to get and set a property to itself, which is not valid. Also a heads up about naming conventions, your public properties should not begin with an underscore, but should follow capital camel casing.
There are two answers to this, both equally valid depending on what you need to do.
METHOD 1: If you take out what it is getting and setting, C# can figure out that there is an implied field that is referenced by the IsNew property. This is essentially shorthand for METHOD 2.
public bool IsNew { get; set; } // shorthand way of creating a property
METHOD 2: Specify a field to get and set.
private bool _isNew; // the field
public bool IsNew { get => _isNew; set => _isNew = value; } // this is the property controlling access to _isNew
Read more information here: Shorthand Accessors and Mutators
Essentially, Use METHOD 1 by default if you don't need to perform any additional operations. However, if you need to provide additional functionality when getting or setting, then use METHOD 2 (I.E. look up the MVVM Pattern for an example https://www.c-sharpcorner.com/UploadFile/raj1979/simple-mvvm-pattern-in-wpf/)
I have a very large class library with >100 POCO objects. I need to serialize these objects into XML to transmit to a REST service.
I've been trying to use DataContractSerializer, but it outputs XML elements with i:nil="true" for any properties that are null. This trips up the REST service to which I'm transmitting XML. Yes, I realize that it shouldn't. The service provider has informed me that correcting the issue will take months. I don't have months to wait for this service to work.
I've been digging through the documentation trying to find a way to suppress these nil objects from being transmitted. I'm aware that I could set the EmitDefaultValue property to false on each individual property of each POCO object. I'm not about to do that for more than 100 objects unless I have no other choice. Furthermore, I don't believe I should be forced to annotate my class library objects with DataContract attributes. I also don't want to mirror my class library with DataContractSurrogates. That is just obscene.
Question
Surely, there is a configuration option somewhere where I can specify that the default behavior for serialization should be EmitDefaultValue = false. I've been unable to find it though. I'm hoping someone else has found it, or has found another global option for suppressing the null properties from the XML.
Can this be specified in app.config/web.config?
Or, can it be set on the DataContractSerializer instance?
If this doesn't exist, it seems like a HUGE oversight by Microsoft.
I believe that there is no official way to set this property globally, maybe because it's described as not recommended practice in most cases.
But there is workaround. You can define your own DataMemberAttribute in System.Runtime.Serialization namespace with EmitDefaultValue set to false by default. Put it somewhere in your project. And that's all you have to do. Compiler will give you a warning saying that your type conflict with imported one, but will use your type after all. I took this class from Microsoft sources, set EmitDefaultValue to false and replace exception throw in order check because it was using internal utility class:
namespace System.Runtime.Serialization
{
[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, Inherited = false, AllowMultiple = false)]
public sealed class DataMemberAttribute : Attribute
{
string name;
bool isNameSetExplicitly;
int order = -1;
bool isRequired;
bool emitDefaultValue = false;
public string Name
{
get { return name; }
set { name = value; isNameSetExplicitly = true; }
}
public bool IsNameSetExplicitly
{
get { return isNameSetExplicitly; }
}
public int Order
{
get { return order; }
set
{
if (order < 0)
throw new InvalidDataContractException();
order = value;
}
}
public bool IsRequired
{
get { return isRequired; }
set { isRequired = value; }
}
public bool EmitDefaultValue
{
get { return emitDefaultValue; }
set { emitDefaultValue = value; }
}
}
}
Now if we take new Foo():
using System.Runtime.Serialization;
namespace FooBar
{
[DataContract]
public class Foo
{
// Warning about type conflict.
[DataMember]
public string Bar { get; set; }
}
}
It will be serialized by DataContractSerializer as:
<Foo xmlns="http://schemas.datacontract.org/2004/07/ConsoleApplication1"
xmlns:i="http://www.w3.org/2001/XMLSchema-instance"/>
my class property has default value which will be serialize.
public class DeclaredValue
{
[XmlElement(ElementName = "Amount", DataType = "double", IsNullable = false), DefaultValue(999)]
public double Amount { get; set; }
[XmlElement(ElementName = "Reference2", DataType = "string", IsNullable = false), DefaultValue("")]
public string Reference2 { get; set; }
}
so we create instance of DeclaredValue class and provide value for Reference2 property and do not assign anything for Amount. so when we serialize the class DeclaredValue then no tag found for amount in my xml. i mention default value for amount "999" then why it does not work in serialization. i want that if do not assign anything for amount then amoun tag should be there in my xml with default value.
to do this what way i need to decorate the amount property that it always comes with default value in xml after serialization if user do not assign anything to this property.
please guide me what i need to change in the code to get my desired output.
Per the note on MSDN:
A DefaultValueAttribute will not cause
a member to be automatically
initialized with the attribute's
value. You must set the initial value
in your code.
Somewhat surprisingly the DefaultValue only regulates the writing of an object, members that are equal to their DefaultValue will not be written out.
You must still initialize members before or after loading yourself, for example in the constructor.
Let me thoroughly describe what is happening.
When XmlSerializer Deserialize() method is called, it creates a new object using a default constructor. It doesn't apply any DefaultValueAttributes to this object, I beleave, because of assumption that default ctor should "know better" how to initialize values by default. From this point of view - it is logical.
XmlSerializer doesn't serialize members which values are the same as marked by DefaultValue attribute. From some point of view such behavior is driven by logic too.
But when you do not initialize members in ctor and call deserialize method, XmlSerializer see no corresponding xml field, but it see that the field/property has DefaultValueAttribute, serializer just leave such value (according to the assumption that the default constructor knows better how to initialize a class "by defaults"). And you've got your zeros.
Solution
To initialize a class members by these DefaultValueAttributes (sometimes it is very handy to have this initialization values just in place) you can use such simple method:
public YourConstructor()
{
LoadDefaults();
}
public void LoadDefaults()
{
//Iterate through properties
foreach (var property in GetType().GetProperties())
{
//Iterate through attributes of this property
foreach (Attribute attr in property.GetCustomAttributes(true))
{
//does this property have [DefaultValueAttribute]?
if (attr is DefaultValueAttribute)
{
//So lets try to load default value to the property
DefaultValueAttribute dv = (DefaultValueAttribute)attr;
try
{
//Is it an array?
if (property.PropertyType.IsArray)
{
//Use set value for arrays
property.SetValue(this, null, (object[])dv.Value);
}
else
{
//Use set value for.. not arrays
property.SetValue(this, dv.Value, null);
}
}
catch (Exception ex)
{
//eat it... Or maybe Debug.Writeline(ex);
}
}
}
}
}
This "public void LoadDefaults()", can be decorated as an Extension to object or use as some static method of a helper class.
As Henk Holterman mentionned, this attribut doesn't set the default value automatically. Its purpose is mostly to be used by visual designers to reset a property to its default value.
As others mentioned, the DefaultValue attribute doesn't initialize the property. You could use a simple loop to set all properties:
foreach (var property in GetType().GetProperties())
property.SetValue(this, ((DefaultValueAttribute)Attribute.GetCustomAttribute(
property, typeof(DefaultValueAttribute)))?.Value, null);
Even though ?.Value could return null, it works with non-nullable types, I tested this.
If only few of your properties have a default value, you should maybe only set the value if it is there.
If all properties should have a default value, remove the ? to get an error if you forgot one.
Most likely, arrays won't work, see MajesticRa's solution how to handle that.
Today, I was cleaning up some of my code with FXCop and it complained about a Attribute class I had with this violation.
CA1019: Define accessor for attribute argument.
On this page, http://msdn.microsoft.com/en-us/library/ms182136.aspx there is more information, but I still do not get the reason for this as it seems to me more verbose and less relevant.
It gives two codes samples.
using System;
namespace DesignLibrary
{
// Violates rule: DefineAccessorsForAttributeArguments.
[AttributeUsage(AttributeTargets.All)]
public sealed class BadCustomAttribute :Attribute
{
string data;
// Missing the property that corresponds to
// the someStringData parameter.
public BadCustomAttribute(string someStringData)
{
data = someStringData;
}
}
// Satisfies rule: Attributes should have accessors for all arguments.
[AttributeUsage(AttributeTargets.All)]
public sealed class GoodCustomAttribute :Attribute
{
string data;
public GoodCustomAttribute(string someStringData)
{
data = someStringData;
}
//The constructor parameter and property
//name are the same except for case.
public string SomeStringData
{
get
{
return data;
}
}
}
}
I don't understand why the SomeStringData property is required. Isn't the someStringData a parameter? Why does it need to have its own property if it is already stored in another property?
Actually, mine is a little different as it looks like this.
[AttributeUsage(AttributeTargets.Property)]
public sealed class ExampleAttribute : Attribute
{
public ExampleAttribute(string attributeValue)
{
this.Path = attributeValue;
}
public string Name
{
get;
set;
}
// Add to add this to stop the CA1019 moaning but I find it useless and stupid?
public string AttributeValue
{
get
{
return this.Name;
}
}
}
Rather than a private field, I have used a public autoproperty, I had to add the last part to make the warning stop but I don't see the point and it also adds another public field to this class, which is redundant, and seems less clean.
That said, I assume that this warning is raised for a reason so what good reason I am missing here?
Thanks in advance.
FxCop is complaining because your existing property doesn't match the parameter name.
Therefore, it doesn't realize that the parameter actually is exposed.
You should rename the property or parameter to match (except for case), or suppress the warning.
FxCop rule CA1019 is just enforcing the .Net Framework coding guidelines for Attributes.
Use named arguments (read/write properties) for optional parameters. Provide a read/write property with the same name as each named argument, but change the case to differentiate between them.
Documentation Link: http://msdn.microsoft.com/en-us/library/2ab31zeh(v=vs.71).aspx
The reason behind the FxCop warning is that every piece of data you pass into the attribute's constructor should be made publicly available to access when the attribute instance is being retrieved by Reflection.
Let's say you have this:
[BadCustom("My String Data")]
public class DecoratedClass
{
}
How will you get "My String Data" back from that attribute instance when you read it using:
BadCustomAttribute attr = typeof(DecoratedClass)
.GetCustomAttributes(typeof(BadCustomAttribute), false)
.Single() as BadCustomAttribute;
Now you have the instance of your attribute, but no way to read the string passed into the constructor because you didn't at least declare a read-only property for it.
the idea is that you should write just:
[AttributeUsage(AttributeTargets.Property)]
public sealed class ExampleAttribute : Attribute
{
public ExampleAttribute(string attributeValue)
{
this.AttributeValue = attributeValue;
}
public string AttributeValue
{
get;
set;
}
}
This violation will also be thrown when the parameter name matches the property name, but the data types are different.
In the code base I was maintaining I found this exact class, pasted below. In logPath property, gets does some work. I would think that it is better to do the work in set - that way it will be done only once. However, partly because this is how the class is written, partly because it is an xml-mapped property, and partly because I am afraid that I might miss something in a debugger, I have doubts.
Additionally, if an element never existed in the xml, and it happened to be optional, then I think I will get a null for the value. I might actually want to differentiate between having no element and receiving empty value. I suppose I can have a private bool member which can help me detect that - that would be an argument for doing work in set rather than get. So, code optimizers work hard these days, so performance is rarely a true concern. It is more of a "figure this out once and do not think about it later" things. This is just one example, and properties frequently do some massaging.
Would you say that it is always better to do work in set? In get? It depends? A mixed style would not bother you a single bit as long as it works?
Thanks.
namespace MyNamespace
{
using System;
using System.Xml.Serialization;
/// <summary>
/// The LoggingListener class encapsulates the "logListener"
/// element of config file, and puts the "logPath"
/// attribute in a file path string.
/// </summary>
public class LoggingListener
{
private string logPathValue;
/// <summary>
/// Gets or sets the LOCAL file path to a log file
/// which will be written during operation of the Updater.
/// </summary>
[XmlAttribute("logPath")]
public string LogPath
{
get
{
return this.logPathValue == null ?
String.Empty : this.logPathValue;
}
set
{
this.logPathValue = value;
}
}
}
}
EDIT: In this given sample ... if the log file is not there, then no logging should take place.
I'd certainly prefer consistency. But the fact is in cases like this it often will not matter. I'm sure the original developer's intent was to avoid the infuriating NullReferenceException bug resulting from attempting to access the LogPath property of some LoggingListener object -- in which case, it probably just seemed most sensible to put the null check in the get (since that's where the exception was thrown).
In general, I'd agree with you that perhaps it makes the most sense to put it in the set -- but then, there's no guaranteeing LogPath will never return null, as the private member could have been set to null from within the class, or perhaps it was never set at all (as Kevin pointed out).
I tend to go with a somewhat hybrid approach: make the property read-only, and make sure it gets set to something non-null in the constructor:
public class LoggingListener {
private readonly string _logPath;
public LoggingListener(string logPath) {
_logPath = logPath ?? string.Empty;
}
public string LogPath {
get { return _logPath; }
}
}
Whether this is an acceptable compromise obviously depends on your specific needs. Also, whether the property should really never be null after all is certainly debatable, depending on the scenario, as you've already remarked.
I personally don't like when property changes assigned value in either get or set accessor. It changes expected property behavior:
var value = null;
var listener = new LoggingListener();
listener.LogPath = value;
if(listener.LogPath != value)
{
// how could we get here?
}
Instead, I prefer to clearly decide, whether property can accept null or not. If it can, it shouldn't do any work in get/set, if yes, it should neither return null nor accept it as a value.
If there is no way to prevent assignment of null, than i would prefer to handle this case in set accessor.
With getters and setters I follow a few rules:
No side effects - don't modify 'B' when you put a value in 'A'
What I put in 'A' comes out of 'A', if you need to modify 'A' expose a new read-only property
If you don't like my value for 'A', tell me now not later when I call a method
Outside of a data model, do not accept or return null
For your example I prefer seeing the following:
public class LoggingListener
{
private string logPathValue = String.Empty;
[XmlAttribute("logPath")]
public string LogPath
{
get { return logPathValue; }
set
{
if(value == null) throw new ArgumentNullException();
this.logPathValue = value;
}
}
}
Yet it's clear to me why you ask, it really about the behavior of "XmlAttribute" and the XmlSerializer. You can use the "DefaultValueAttribute" from the ComponentModel namespace, or use an XSD to provide the defaults, or expose a new property and/or method. You could also try creating an interface to separate concerns, something like the following:
public class LoggingListener : ILogListenerSettings
{
private string logPathValue;
[XmlAttribute("logPath")]
public string LogPath
{
get { return logPathValue; }
set { logPathValue = value; }
}
string ILogListenerSettings.FullLogPath
{
get
{
string path = logPathValue;
if(String.IsNullOrEmpty(path))
path = Environment.CurrentDirectory;
path = Path.GetFullPath(path);
Directory.Create(path);
return path;
}
}
}
the only way to be sure that logPathValue is initialized is to do it yourself...
public class LoggingListener
{
private string logPathValue = string.Empty;