How to check if IEnumerable is null or empty

Question

I love string IsNullOrEmpty method  I d love to have something that would allow the same functionality for IEnumerable  Is there such  Maybe some collection helper class  The reason I am asking is that in if statements the code looks cluttered if the patter is  mylist    null  amp  amp  mylist Any     It would be much cleaner to have Foo IsAny myList     This post doesn t give that answer  IEnumerable is empty

User · Answer

The other best solution as below to check empty or not    for var item in listEnumerable     var count item Length    if count gt 0                  not empty or null        else               empty

User · Answer

I use      list Where  r  gt r value    value  DefaultIfEmpty   First     The result will be null if no match  otherwise returns one of the objects  If you wanted the list  I believe leaving of First   or calling ToList   will provide the list or null

User · Answer

Take a look at this opensource library  Nzr ToolBox  public static bool IsEmpty this System Collections IEnumerable enumerable

User · Answer

The way I do it  taking advantage of some modern C  features   Option 1   public static class Utils       public static bool IsNullOrEmpty lt T gt  this IEnumerable lt T gt  list            return   list  Any      false             Option 2   public static class Utils       public static bool IsNullOrEmpty lt T gt  this IEnumerable lt T gt  list            return   list  Any    GetValueOrDefault              And by the way  never use Count    0 or Count      0 just to check if a collection is empty  Always use Linq s  Any

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Since some resources are exhausted after one read  I thought why not combine the checks and the reads  instead of the traditional separate check  then read    First we have one for the simpler check-for-null inline extension   public static System Collections Generic IEnumerable lt T gt  ThrowOnNull lt T gt  this System Collections Generic IEnumerable lt T gt  source  string paramName   null    gt  source    throw new System ArgumentNullException paramName    nameof source     var first   source ThrowOnNull   First      Then we have the little more involved  well  at least the way I wrote it  check-for-null-and-empty inline extension   public static System Collections Generic IEnumerable lt T gt  ThrowOnNullOrEmpty lt T gt  this System Collections Generic IEnumerable lt T gt  source  string paramName   null      using  var e   source ThrowOnNull paramName  GetEnumerator            if   e MoveNext                throw new System ArgumentException   The sequence is empty    paramName    nameof source               do             yield return e Current            while  e MoveNext            var first   source ThrowOnNullOrEmpty   First      You can of course still call both without continuing the call chain  Also  I included the paramName  so that the caller may include an alternate name for the error if it s not  source  being checked  e g   nameof target

User · Answer

if  collection  Any      true          if collection contains more than one item   if  collection  Any      true          if collection is null        if collection does not contain any item

User · Answer

I use this one       public static bool IsNotEmpty this ICollection elements                return elements    null  amp  amp  elements Count  gt  0          Ejem   List lt string gt  Things   null  if  Things IsNotEmpty            replaces - gt   if  Things    null  amp  amp  Things Count  gt  0

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Jon Skeet s anwser  https   stackoverflow com a 28904021 8207463   has a good approach using Extension Method - Any   for NULL and EMPTY  BUT he  s validating the questions  owner in case for NOT  NULL   So carefully change Jon  s approach to validate AS NULL to   If  yourList  Any      true            your code        DO NOT use   will not validate AS NULL    If  yourList  Any      false            your code        You can also in case validating AS NOT NULL   NOT tested just as example but without compiler error  do something like using predicate    If  yourList  Any p   gt  p anyItem    null     true            your code        https   referencesource microsoft com  System Core System Linq Enumerable cs 8788153112b7ffd0  For which  NET version you can use it please check   https   docs microsoft com en-us dotnet api system linq enumerable any view netframework-4 8 moniker-applies-to

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I had the same problem and I solve it like         public bool HasMember IEnumerable lt TEntity gt  Dataset                return Dataset    null  amp  amp  Dataset Any c  gt c  null            c  c  null  will ignore all the null entities

User · Answer

just add using System Linq and see the magic happening when you try to access the available methods in the IEnumerable  Adding this will give you access to method named Count   as simple as that  just remember to check for null value before calling count

User · Answer

Starting with C 6 you can use null propagation  myList  Any      true  If you still find this too cloggy or prefer a good ol  extension method  I would recommend Matt Greer and Marc Gravell s answers  yet with a bit of extended functionality for completeness    Their answers provide the same basic functionality  but each from another perspective  Matt s answer uses the string IsNullOrEmpty-mentality  whereas Marc s answer takes Linq s  Any   road to get the job done   I am personally inclined to use the  Any   road  but would like to add the condition checking functionality from the method s other overload       public static bool AnyNotNull lt T gt  this IEnumerable lt T gt  source  Func lt T  bool gt  predicate   null                if  source    null  return false          return predicate    null               source Any                 source Any predicate           So you can still do things like    myList AnyNotNull item  gt item AnswerToLife    42   as you could with the regular  Any   but with the added null check  Note that with the C 6 way  myList  Any   returns a bool  rather than a bool  which is the actual effect of propagating null

User · Answer

Here s a modified version of  Matt Greer s useful answer that includes a static wrapper class so you can just copy-paste this into a new source file  doesn t depend on Linq  and adds a generic IEnumerable lt T gt  overload  to avoid the boxing of value types that would occur with the non-generic version   EDIT  Note that use of IEnumerable lt T gt  does not prevent boxing of the enumerator  duck-typing can t prevent that  but at least the elements in a value-typed collection will not each be boxed    using System Collections  using System Collections Generic   public static class IsNullOrEmptyExtension       public static bool IsNullOrEmpty this IEnumerable source                if  source    null                        foreach  object obj in source                                return false                                  return true             public static bool IsNullOrEmpty lt T gt  this IEnumerable lt T gt  source                if  source    null                        foreach  T obj in source                                return false                                  return true

User · Answer

Sure you could write that   public static class Utils       public static bool IsAny lt T gt  this IEnumerable lt T gt  data            return data    null  amp  amp  data Any              however  be cautious that not all sequences are repeatable  generally I prefer to only walk them once  just in case

User · Answer

Without custom helpers I recommend either   Any      false or   Any      true which are relatively concise and only need to specify the sequence once     When I want to treat a missing collection like an empty one  I use the following extension method   public static IEnumerable lt T gt  OrEmpty lt T gt  this IEnumerable lt T gt  sequence        return sequence    Enumerable Empty lt T gt         This function can be combined with all LINQ methods and foreach  not just  Any    which is why I prefer it over the more specialized helper functions people are proposing here

User · Answer

public static bool IsNullOrEmpty lt T gt  this IEnumerable lt T gt  enumerable        return enumerable    null     enumerable Any

User · Answer

Another way would be to get the Enumerator and call the MoveNext   method to see if there are any items   if  mylist    null  amp  amp  mylist GetEnumerator   MoveNext             The list is not null or empty     This works for IEnumerable as well as IEnumerable lt T gt

User · Answer

I built this off of the answer by  Matt Greer  He answered the OP s question perfectly   I wanted something like this while maintaining the original capabilities of Any while also checking for null  I m posting this in case anyone else needs something similar   Specifically I wanted to still be able to pass in a predicate   public static class Utilities            lt summary gt          Determines whether a sequence has a value and contains any elements           lt  summary gt           lt typeparam name  TSource  gt The type of the elements of source  lt  typeparam gt           lt param name  source  gt The  lt see cref  System Collections Generic IEnumerable   gt  to check for emptiness  lt  param gt           lt returns gt true if the source sequence is not null and contains any elements  otherwise  false  lt  returns gt      public static bool AnyNotNull lt TSource gt  this IEnumerable lt TSource gt  source                return source  Any      true                  lt summary gt          Determines whether a sequence has a value and any element of a sequence satisfies a condition           lt  summary gt           lt typeparam name  TSource  gt The type of the elements of source  lt  typeparam gt           lt param name  source  gt An  lt see cref  System Collections Generic IEnumerable   gt  whose elements to apply the predicate to  lt  param gt           lt param name  predicate  gt A function to test each element for a condition  lt  param gt           lt returns gt true if the source sequence is not null and any elements in the source sequence pass the test in the specified predicate  otherwise  false  lt  returns gt      public static bool AnyNotNull lt TSource gt  this IEnumerable lt TSource gt  source  Func lt TSource  bool gt  predicate                return source  Any predicate     true            The naming of the extension method could probably be better

User · Answer

public static bool AnyNotNull lt TSource gt  this IEnumerable lt TSource gt  source                return source    null  amp  amp  source Any            my own extension method to check Not null and Any

User · Answer

Here s the code from Marc Gravell s answer  along with an example of using it   using System  using System Collections Generic  using System Linq   public static class Utils       public static bool IsAny lt T gt  this IEnumerable lt T gt  data                return data    null  amp  amp  data Any             class Program       static void Main string   args                IEnumerable lt string gt  items            items   null            items   new String 0           items   new String      foo    bar    baz                   Example Starts Here              if  items IsAny                          foreach  var item in items                                Console WriteLine item                                   else                       Console WriteLine  No items                         As he says  not all sequences are repeatable  so that code may sometimes cause problems  because IsAny   starts stepping through the sequence  I suspect what Robert Harvey s answer meant was that you often don t need to check for null and empty  Often  you can just check for null and then use foreach   To avoid starting the sequence twice and take advantage of foreach  I just wrote some code like this   using System  using System Collections Generic  using System Linq   class Program       static void Main string   args                IEnumerable lt string gt  items            items   null            items   new String 0           items   new String      foo    bar    baz                   Example Starts Here              bool isEmpty   true          if  items    null                        foreach  var item in items                                isEmpty   false                  Console WriteLine item                                   if  isEmpty                        Console WriteLine  No items                         I guess the extension method saves you a couple of lines of typing  but this code seems clearer to me  I suspect that some developers wouldn t immediately realize that IsAny items  will actually start stepping through the sequence   Of course if you re using a lot of sequences  you quickly learn to think about what steps through them

User · Answer

I use Bool IsCollectionNullOrEmpty     Collection  Any    false    Hope this helps   Breakdown   Collection  Any   will return null if Collection is null  and false if Collection is empty   Collection  Any    false will give us false if Collection is empty  and false if Collection is null   Complement of that will give us IsEmptyOrNull

User · Answer

This may help  public static bool IsAny lt T gt  this IEnumerable lt T gt  enumerable        return enumerable  Any      true     public static bool IsNullOrEmpty lt T gt  this IEnumerable lt T gt  enumerable        return enumerable  Any      true

User · Answer

I used simple if to check for it  check out my solution  foreach  Pet pet in v Pets        if  pet    null                Console WriteLine   No pet      enumerator is empty         break            Console WriteLine     0    pet Name

[c#] How to check if IEnumerable is null or empty?

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