Most Useful Attributes

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I know that attributes are extremely useful  There are some predefined ones such as  Browsable false   which allows you to hide properties in the properties tab  Here is a good question explaining attributes  What are attributes in  NET   What are the predefined attributes  and their namespace  you actually use in your projects

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DebuggerDisplay  can be really helpful to quickly see customized output of a Type when you mouse over the instance of the Type during debugging  example    DebuggerDisplay  FirstName  FirstName   LastName  LastName     class Customer       public string FirstName      public string LastName      This is how it should look in the debugger     Also  it is worth mentioning that  WebMethod  attribute with CacheDuration property set can avoid unnecessary execution of the web service method

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The attributes I use the most are the ones related to XML Serialization   XmlRoot  XmlElement  XmlAttribute  etc     Extremely useful when doing any quick and dirty XML parsing or serializing

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I ve found  DefaultValue  to be quite useful

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I like  DebuggerStepThrough  from System Diagnostics    It s very handy for avoiding stepping into those one-line do-nothing methods or properties  if you re forced to work in an early  Net without automatic properties   Put the attribute on a short method or the getter or setter of a property  and you ll fly right by even when hitting  step into  in the debugger

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The DebuggerHiddenAttribute which allows to avoiding step into code which should not be debugged   public static class CustomDebug        DebuggerHidden      public static void Assert Boolean condition  Func lt Exception gt  exceptionCreator                     The following assert fails  and because of the attribute the exception is shown at this line    Isn t affecting the stack trace CustomDebug Assert false       gt  new Exception        Also it prevents from showing methods in stack trace  useful when having a method which just wraps another method    DebuggerHidden  public Element GetElementAt Vector2 position        return GetElementAt position X  position Y      public Element GetElementAt Single x  Single y            If you now call GetElementAt new Vector2 10  10   and a error occurs at the wrapped method  the call stack is not showing the method which is calling the method which throws the error

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In our current project  we use   ComVisible false     It controls accessibility of an individual managed type or member  or of all types within an assembly  to COM   More Info

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Flags  is pretty handy  Syntactic sugar to be sure  but still rather nice    Flags   enum SandwichStuff      Cheese   1     Pickles   2     Chips   4     Ham   8     Eggs   16     PeanutButter   32     Jam   64     public Sandwich MakeSandwich SandwichStuff stuff       Console WriteLine stuff ToString                          MakeSandwich SandwichStuff Cheese       SandwichStuff Ham       SandwichStuff PeanutButter      produces console output   Cheese  Ham  PeanutButter      Leppie points out something I hadn t realized  and which rather dampens my enthusiasm for this attribute  it does not instruct the compiler to allow bit combinations as valid values for enumeration variables  the compiler allows this for enumerations regardless  My C   background showing through    sigh

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My vote would be for Conditional   Conditional  DEBUG    public void DebugOnlyFunction            your code here     You can use this to add a function with advanced debugging features  like Debug Write  it is only called in debug builds  and so allows you to encapsulate complex debug logic outside the main flow of your program

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I have been using the  DataObjectMethod  lately  It describes the method so you can use your class with the ObjectDataSource   or other controls     DataObjectMethod DataObjectMethodType Select     DataObjectMethod DataObjectMethodType Delete     DataObjectMethod DataObjectMethodType Update     DataObjectMethod DataObjectMethodType Insert      More info

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In our current project  we use   ComVisible false     It controls accessibility of an individual managed type or member  or of all types within an assembly  to COM   More Info

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I generates data entity class via CodeSmith and I use attributes for some validation routine  Here is an example        lt summary gt      Firm ID      lt  summary gt   ChineseDescription             ValidRequired    public string FirmGUID       get   return  firmGUID        set    firmGUID   value        And I got an utility class to do the validation based on the attributes attached to the data entity class  Here is the code   namespace Reform Water Business Common        lt summary gt      Validation Utility      lt  summary gt  public static class ValidationUtility            lt summary gt          Data entity validation          lt  summary gt           lt param name  data  gt Data entity object lt  param gt           lt returns gt return true if the object is valid  otherwise return false lt  returns gt      public static bool Validate object data                bool result   true          PropertyInfo   properties   data GetType   GetProperties            foreach  PropertyInfo p in properties                          Length validatioin             Attribute attribute   Attribute GetCustomAttribute p typeof ValidLengthAttribute   false               if  attribute    null                                ValidLengthAttribute validLengthAttribute   attribute as ValidLengthAttribute                  if  validLengthAttribute    null                                        int maxLength   validLengthAttribute MaxLength                      int minLength   validLengthAttribute MinLength                      string stringValue   p GetValue data  null  ToString                        if  stringValue Length  lt  minLength    stringValue Length  gt  maxLength                                                return false                                                                      Range validation             attribute   Attribute GetCustomAttribute p typeof ValidRangeAttribute   false               if  attribute    null                                ValidRangeAttribute validRangeAttribute   attribute as ValidRangeAttribute                  if  validRangeAttribute    null                                        decimal maxValue   decimal MaxValue                      decimal minValue   decimal MinValue                      decimal TryParse validRangeAttribute MaxValueString  out maxValue                       decimal TryParse validRangeAttribute MinValueString  out minValue                       decimal decimalValue   0                      decimal TryParse p GetValue data  null  ToString    out decimalValue                       if  decimalValue  lt  minValue    decimalValue  gt  maxValue                                                return false                                                                      Regex validation             attribute   Attribute GetCustomAttribute p typeof ValidRegExAttribute   false               if  attribute    null                                ValidRegExAttribute validRegExAttribute   attribute as ValidRegExAttribute                  if  validRegExAttribute    null                                        string objectStringValue   p GetValue data  null  ToString                        string regExString   validRegExAttribute RegExString                      Regex regEx   new Regex regExString                       if  regEx Match objectStringValue     null                                                return false                                                                      Required field validation             attribute   Attribute GetCustomAttribute p typeof ValidRequiredAttribute   false               if  attribute    null                                ValidRequiredAttribute validRequiredAttribute   attribute as ValidRequiredAttribute                  if  validRequiredAttribute    null                                        object requiredPropertyValue   p GetValue data  null                       if  requiredPropertyValue    null    string IsNullOrEmpty requiredPropertyValue ToString                                                   return false                                                                          return result

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If I were to do a code coverage crawl  I think these two would be top     Serializable    WebMethod

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I like using the  ThreadStatic  attribute in combination with thread and stack based programming   For example  if I want a value that I want to share with the rest of a call sequence  but I want to do it out of band  i e  outside of the call parameters   I might employ something like this   class MyContextInformation   IDisposable        ThreadStatic  private static MyContextInformation current       public static MyContextInformation Current           get   return current               private MyContextInformation previous        public MyContextInformation Object myData           this myData   myData         previous   current         current   this             public void Dispose            current   previous            Later in my code  I can use this to provide contextual information out of band to people downstream from my code   Example   using new MyContextInformation someInfoInContext                The ThreadStatic attribute allows me to scope the call only to the thread in question avoiding the messy problem of data access across threads

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It s not well-named  not well-supported in the framework  and shouldn t require a parameter  but this attribute is a useful marker for immutable classes    ImmutableObject true

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I always use the DisplayName  Description and DefaultValue attributes over public properties of my user controls  custom controls or any class I ll edit through a property grid  These tags are used by the  NET PropertyGrid to format the name  the description panel  and bolds values that are not set to the default values    DisplayName  Error color     Description  The color used on nodes containing errors      DefaultValue Color Red   public Color ErrorColor                I just wish Visual Studio s IntelliSense would take the Description attribute into account if no XML comment are found  It would avoid having to repeat the same sentence twice

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DeploymentItem  myFile1 txt    MSDN Doc on DeploymentItem  This is really useful if you are testing against a file or using the file as input to your test

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TypeConverter typeof ExpandableObjectConverter      Tells the designer to expand the properties which are classes  of your control    Obfuscation    Instructs obfuscation tools to take the specified actions for an assembly  type  or member   Although typically you use an Assembly level  assembly ObfuscateAssemblyAttribute true

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on configuration sections  ConfigurationProperty       in asp net  NotifyParentProperty true

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XmlIgnore    as this allows you to ignore  in any xml serialisation   parent  objects that would otherwise cause exceptions when saving

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I have been using the  DataObjectMethod  lately  It describes the method so you can use your class with the ObjectDataSource   or other controls     DataObjectMethod DataObjectMethodType Select     DataObjectMethod DataObjectMethodType Delete     DataObjectMethod DataObjectMethodType Update     DataObjectMethod DataObjectMethodType Insert      More info

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EditorBrowsable EditorBrowsableState Never   allows you to hide properties and methods from IntelliSense if the project is not in your solution  Very helpful for hiding invalid flows for fluent interfaces  How often do you want to GetHashCode   or Equals     For MVC  ActionName  Name    allows you to have a Get action and Post action with the same method signature  or to use dashes in the action name  which otherwise would not be possible without creating a route for it

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Only a few attributes get compiler support  but one very interesting use of attributes is in AOP  PostSharp uses your bespoke attributes to inject IL into methods  allowing all manner of abilities    log trace being trivial examples - but some other good examples are things like automatic INotifyPropertyChanged implementation  here    Some that occur and impact the compiler or runtime directly     Conditional  FOO    - calls to this method  including argument evaluation  only occur if the  FOO  symbol is defined during build  MethodImpl       - used to indicate a few thing like synchronization  inlining  PrincipalPermission       - used to inject security checks into the code automatically  TypeForwardedTo       - used to move types between assemblies without rebuilding the callers   For things that are checked manually via reflection - I m a big fan of the System ComponentModel attributes  things like  TypeDescriptionProvider         TypeConverter         and  Editor       which can completely change the behavior of types in data-binding scenarios  i e  dynamic properties etc

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I like using the  ThreadStatic  attribute in combination with thread and stack based programming   For example  if I want a value that I want to share with the rest of a call sequence  but I want to do it out of band  i e  outside of the call parameters   I might employ something like this   class MyContextInformation   IDisposable        ThreadStatic  private static MyContextInformation current       public static MyContextInformation Current           get   return current               private MyContextInformation previous        public MyContextInformation Object myData           this myData   myData         previous   current         current   this             public void Dispose            current   previous            Later in my code  I can use this to provide contextual information out of band to people downstream from my code   Example   using new MyContextInformation someInfoInContext                The ThreadStatic attribute allows me to scope the call only to the thread in question avoiding the messy problem of data access across threads

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Being a middle tier developer I like  System ComponentModel EditorBrowsableAttribute Allows me to hide properties so that the UI developer is not overwhelmed with properties that they don t need to see   System ComponentModel BindableAttribute Some things don t need to be databound  Again  lessens the work the UI developers need to do   I also like the DefaultValue that Lawrence Johnston mentioned   System ComponentModel BrowsableAttribute and the Flags are used regularly   I use  System STAThreadAttribute       System ThreadStaticAttribute when needed   By the way  I these are just as valuable for all the  Net framework developers

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Off the top of my head  here is a quick list  roughly sorted by frequency of use  of predefined attributes I actually use in a big project   500k LoCs    Flags  Serializable  WebMethod  COMVisible  TypeConverter  Conditional  ThreadStatic  Obsolete  InternalsVisibleTo  DebuggerStepThrough

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I consider that is important to mention here that the following attributes are also very important   STAThreadAttribute    Indicates that the COM threading model for an application is single-threaded apartment  STA     For example this attribute is used in Windows Forms Applications   static class Program            lt summary gt          The main entry point for the application           lt  summary gt       STAThread      static void Main                 Application EnableVisualStyles            Application SetCompatibleTextRenderingDefault false           Application Run new Form1               And also      SuppressMessageAttribute   Suppresses reporting of a specific static analysis tool rule violation  allowing multiple suppressions on a single code artifact   For example    SuppressMessage  Microsoft Performance    CA1801 ReviewUnusedParameters   MessageId    isChecked     SuppressMessage  Microsoft Performance    CA1804 RemoveUnusedLocals   MessageId    fileIdentifier    static void FileNode string name  bool isChecked        string fileIdentifier   name      string fileName   name      string version   String Empty

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Serializable  is used all the time for serializing and deserializing objects to and from external data sources such as xml or from a remote server  More about it here

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System Obsolete is one of the most useful attributes in the framework  in my opinion  The ability to raise a warning about code that should no longer be used is very useful  I love having a way to tell developers that something should no longer be used  as well as having a way to explain why and point to the better new way of doing something   The Conditional attribute is pretty handy too for debug usage  It allows you to add methods in your code for debug purposes that won t get compiled when you build your solution for release   Then there are a lot of attributes specific to Web Controls that I find useful  but those are more specific and don t have any uses outside of the development of server controls from what I ve found

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For what it s worth  here s a list of all  NET attributes   There are several hundred   I don t know about anyone else but I have some serious RTFM to do

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DesignerSerializationVisibilityAttribute is very useful  When you put a runtime property on a control or component  and you don t want the designer to serialize it  you use it like this    DesignerSerializationVisibility DesignerSerializationVisibility Hidden   public Foo Bar       get   return baz        set   baz   value

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DesignerSerializationVisibilityAttribute is very useful  When you put a runtime property on a control or component  and you don t want the designer to serialize it  you use it like this    DesignerSerializationVisibility DesignerSerializationVisibility Hidden   public Foo Bar       get   return baz        set   baz   value

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I always use attributes   Serializable    WebMethod     DefaultValue    Description  description here      but beside that there is a Global Attributes in c     assembly  System CLSCompliant true    assembly  AssemblyCulture       assembly  AssemblyDescription

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System Security Permissions PermissionSetAttribute  allows security actions for a PermissionSet to be applied to code using declarative security      usage  public class FullConditionUITypeEditor   UITypeEditor          The immediate caller is required to have been granted the FullTrust permission       PermissionSetAttribute SecurityAction LinkDemand  Name    FullTrust        public FullConditionUITypeEditor

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I d suggest  TestFixture  and  Test  - from the nUnit library   Unit tests in your code provide safety in refactoring and codified documentation

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TypeConverter typeof ExpandableObjectConverter      Tells the designer to expand the properties which are classes  of your control    Obfuscation    Instructs obfuscation tools to take the specified actions for an assembly  type  or member   Although typically you use an Assembly level  assembly ObfuscateAssemblyAttribute true

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In Hofstadtian spirit  the  Attribute  attribute is very useful  since it s how you create your own attributes  I ve used attributes instead of interfaces to implement plugin systems  add descriptions to Enums  simulate multiple dispatch and other tricks

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on configuration sections  ConfigurationProperty       in asp net  NotifyParentProperty true

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Here is the post about interesting attribute InternalsVisibleTo  Basically what it does it mimics C   friends access functionality  It comes very handy for unit testing

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XmlIgnore    as this allows you to ignore  in any xml serialisation   parent  objects that would otherwise cause exceptions when saving

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