Question

I have this class.

public class Foo {     public Guid Id { get; set; }      public override bool Equals(object obj)     {         Foo otherObj = obj as Foo;          return otherObj == null && otherObj.Id == this.Id;     }      public override int GetHashCode()     {         return this.Id.GetHashCode();     } } 

You can see I overrode the Equals and GetHashCode for this object.

Now I run the following snippet of code

// Create Foo List List<Foo> fooList = new List<Foo>();  fooList.Add(new Foo { Id = Guid.NewGuid()}); fooList.Add(new Foo { Id = Guid.NewGuid()}); fooList.Add(new Foo { Id = Guid.NewGuid()}); fooList.Add(new Foo { Id = Guid.NewGuid()}); fooList.Add(new Foo { Id = Guid.NewGuid()});  // Keep Id of last Create Guid id = Guid.NewGuid();  fooList.Add(new Foo { Id = id });  Console.WriteLine('List Count {0}', fooList.Count);  // Find Foo in List Foo findFoo = fooList     .Where<Foo>(item => item.Id == id)     .FirstOrDefault<Foo>();  if (findFoo != null) {     Console.WriteLine('Found Foo');      // Found Foo now I want to delete it from list     fooList.Remove(findFoo); }  Console.WriteLine('List Count {0}', fooList.Count); 

When this is run foo is found, but the list doesn’t delete the found item.

Why is this? I thought overrideing the Equals and GetHashCode should fix this?

Answer 1

return otherObj == null && otherObj.Id == this.Id; 

Is that correct? Shouldn’t it be

return otherObj != null && otherObj.Id == this.Id;