How to access property of anonymous type in C

Question

I have this   List lt object gt  nodes   new List lt object gt       nodes Add  new       Checked       false      depth         1      id             div     d Id           and I m wondering if I can then grab the  Checked  property of the anonymous object   I m not sure if this is even possible   Tried doing this   if  nodes Any n   gt  n  Checked      false        but it doesn t work   Thanks

User · Accepted Answer

If you want a strongly typed list of anonymous types, you'll need to make the list an anonymous type too. The easiest way to do this is to project a sequence such as an array into a list, e.g.

var nodes = (new[] { new { Checked = false, /* etc */ } }).ToList();

Then you'll be able to access it like:

nodes.Any(n => n.Checked);

Because of the way the compiler works, the following then should also work once you have created the list, because the anonymous types have the same structure so they are also the same type. I don't have a compiler to hand to verify this though.

nodes.Add(new { Checked = false, /* etc */ });

User · Answer

If you re storing the object as type object  you need to use reflection  This is true of any object type  anonymous or otherwise  On an object o  you can get its type   Type t   o GetType      Then from that you look up a property   PropertyInfo p   t GetProperty  Foo      Then from that you can get a value   object v   p GetValue o  null     This answer is long overdue for an update for C  4   dynamic d   o  object v   d Foo    And now another alternative in C  6   object v   o  GetType   GetProperty  Foo    GetValue o  null     Note that by using    we cause the resulting v to be null in three different situations     o is null  so there is no object at all o is non-null but doesn t have a property Foo o has a property Foo but its real value happens to be null    So this is not equivalent to the earlier examples  but may make sense if you want to treat all three cases the same

User · Answer

Recently  I had the same problem within  NET 3 5  no dynamic available    Here is how I solved      pass anonymous object as argument var args   new   Title    Find   Type   typeof FindCondition      using  frmFind f   new frmFind args                  Adapted from somewhere on stackoverflow      Use a custom cast extension public static T CastTo lt T gt  this Object x  T targetType       return  T x      Now get back the object via cast   public partial class frmFind  Form       public frmFind object arguments                 InitializeComponent             var args   arguments CastTo new   Title       Type   typeof Nullable               this Text   args Title

User · Answer

You could iterate over the anonymous type s properties using Reflection  see if there is a  Checked  property and if there is then get its value   See this blog post  http   blogs msdn com wriju archive 2007 10 26 c-3-0-anonymous-type-and-net-reflection-hand-in-hand aspx  So something like   foreach object o in nodes        Type t   o GetType         PropertyInfo   pi   t GetProperties          foreach  PropertyInfo p in pi                if  p Name   Checked   amp  amp    bool p GetValue o               Console WriteLine  awesome

User · Answer

The accepted answer correctly describes how the list should be declared and is highly recommended for most scenarios  But I came across a different scenario  which also covers the question asked  What if you have to use an existing object list  like ViewData  quot htmlAttributes quot   in MVC  How can you access its properties  they are usually created via new    style  quot width  100px quot           For this slightly different scenario I want to share with you what I found out  In the solutions below  I am assuming the following declaration for nodes  List lt object gt  nodes   new List lt object gt      nodes Add  new       Checked   false      depth   1      id    quot div 1 quot        1  Solution with dynamic In C  4 0 and higher versions  you can simply cast to dynamic and write  if  nodes Any n   gt    dynamic n  Checked    false       Console WriteLine  quot found a  not checked  element  quot     Note  This is using late binding  which means it will recognize only at runtime if the object doesn t have a Checked property and throws a RuntimeBinderException in this case - so if you try to use a non-existing Checked2 property you would get the following message at runtime   quot   lt  gt f  AnonymousType0 lt bool int string gt   does not contain a definition for  Checked2  quot   2  Solution with reflection The solution with reflection works both with old and new C  compiler versions  For old C  versions please regard the hint at the end of this answer  Background As a starting point  I found a good answer here  The idea is to convert the anonymous data type into a dictionary by using reflection  The dictionary makes it easy to access the properties  since their names are stored as keys  you can access them like myDict  quot myProperty quot     Inspired by the code in the link above  I created an extension class providing GetProp  UnanonymizeProperties and UnanonymizeListItems as extension methods  which simplify access to anonymous properties  With this class you can simply do the query as follows  if  nodes UnanonymizeListItems   Any n   gt   bool n  quot Checked quot      false         Console WriteLine  quot found a  not checked  element  quot       or you can use the expression nodes UnanonymizeListItems x   gt   bool x  quot Checked quot      false  Any   as if condition  which filters implicitly and then checks if there are any elements returned  To get the first object containing  quot Checked quot  property and return its property  quot depth quot   you can use  var depth   nodes UnanonymizeListItems                  FirstOrDefault n   gt  n Contains  quot Checked quot    GetProp  quot depth quot     or shorter  nodes UnanonymizeListItems    FirstOrDefault n   gt  n Contains  quot Checked quot      quot depth quot    Note  If you have a list of objects which don t necessarily contain all properties  for example  some do not contain the  quot Checked quot  property   and you still want to build up a query based on  quot Checked quot  values  you can do this  if  nodes UnanonymizeListItems x   gt    var y     bool  x GetProp  quot Checked quot   true                                           return y HasValue  amp  amp  y Value    false    Any          Console WriteLine  quot found a  not checked   element  quot       This prevents  that a KeyNotFoundException occurs if the  quot Checked quot  property does not exist   The class below contains the following extension methods   UnanonymizeProperties  Is used to de-anonymize the properties contained in an object  This method uses reflection  It converts the object into a dictionary containing the properties and its values  UnanonymizeListItems  Is used to convert a list of objects into a list of dictionaries containing the properties  It may optionally contain a lambda expression to filter beforehand  GetProp  Is used to return a single value matching the given property name  Allows to treat not-existing properties as null values  true  rather than as KeyNotFoundException  false   For the examples above  all that is required is that you add the extension class below  public static class AnonymousTypeExtensions          makes properties of object accessible      public static IDictionary UnanonymizeProperties this object obj                Type type   obj  GetType            var properties   type  GetProperties                    Select n   gt  n Name                   ToDictionary k   gt  k  k   gt  type GetProperty k  GetValue obj  null            return properties                    converts object list into list of properties that meet the filterCriteria     public static List lt IDictionary gt  UnanonymizeListItems this List lt object gt  objectList                       Func lt IDictionary lt string  object gt   bool gt  filterCriteria default                var accessibleList   new List lt IDictionary gt             foreach  object obj in objectList                        var props   obj UnanonymizeProperties                if  filterCriteria    default                   filterCriteria  IDictionary lt string  object gt  props     true                accessibleList Add props                       return accessibleList                returns specific property  i e  obj GetProp propertyName         requires prior usage of AccessListItems and selection of one element  because        object needs to be a IDictionary lt string  object gt      public static object GetProp this object obj  string propertyName                                    bool treatNotFoundAsNull   false                try                        return   System Collections Generic IDictionary lt string  object gt  obj                       propertyName                     catch  KeyNotFoundException                        if  treatNotFoundAsNull  return default object   else throw                     Hint  The code above is using the null-conditional operators  available since C  version 6 0 - if you re working with older C  compilers  e g  C  3 0   simply replace    by   and    by   everywhere  and do the null-handling traditionally by using if statements or catch NullReferenceExceptions   e g  var depth   nodes UnanonymizeListItems                FirstOrDefault n   gt  n Contains  quot Checked quot     quot depth quot     As you can see  the null-handling without the null-conditional operators would be cumbersome here  because everywhere you removed them you have to add a null check - or use catch statements where it is not so easy to find the root cause of the exception resulting in much more - and hard to read - code  If you re not forced to use an older C  compiler  keep it as is  because using null-conditionals makes null handling much easier  Note  Like the other solution with dynamic  this solution is also using late binding  but in this case you re not getting an exception - it will simply not find the element if you re referring to a non-existing property  as long as you keep the null-conditional operators  What might be useful for some applications is that the property is referred to via a string in solution 2  hence it can be parameterized

[c#] How to access property of anonymous type in C#?

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