c# DirectoryInfo and Except

Question

I perform the following code and the result is puzzling me

System.IO.DirectoryInfo rootDir = 
      new System.IO.DirectoryInfo(@"\\share\data");

// AllDir  == 10 folders

System.IO.DirectoryInfo[] AllDir = 
      rootDir.GetDirectories("*.*", SearchOption.AllDirectories);

// JackDir  == 2 folders

System.IO.DirectoryInfo[] JackDir = 
      rootDir.GetDirectories("Jack*.*", SearchOption.AllDirectories);

// MaryDir == 3 folders

System.IO.DirectoryInfo[] MaryDir = 
      rootDir.GetDirectories("Mary*.*", SearchOption.AllDirectories);

System.IO.DirectoryInfo[] otherDirectory = 
      AllDir.Except<DirectoryInfo>(MaryDir).Except(JackDir).ToArray();

And otherDirectory in the end still has 10 folders...why not 5? How can I achieve this?

Answer 1

You are comparing DirectoryInfo instances. They are not the same as they are returned by different calls to GetDirectories .

You can define your own comparer for DirectoryInfo comparing FullName and use it in your calls to Except .

public class DirectoryInfoComparer : IEqualityComparer<System.IO.DirectoryInfo>
{
  public bool Equals(System.IO.DirectoryInfo x, System.IO.DirectoryInfo y)
  {
    if (object.ReferenceEquals(x, y))
      return true;
    if (x == null || y == null)
      return false;
    return x.FullName == y.FullName;
  }

  public int GetHashCode(System.IO.DirectoryInfo obj)
  {
    if (obj == null)
      return 0;
    return obj.FullName.GetHashCode();
  }
}


System.IO.DirectoryInfo[] otherDirectory = 
      AllDir.Except<DirectoryInfo>(MaryDir, new DirectoryInfoComparer()).Except(JackDir, new DirectoryInfoComparer()).ToArray();

Answer 2

You need to provide a custom comparer, You see this behavior because it is tested equality against "Reference comparison" and of course they are different references.

Use Except method overload which takes IEqualityComparer as parameter to achieve the desired output.