Bookmark Collection: Retrieving a bookmark that is not in the collection

Let's see where we were...

• Retrieve a Bookmark that is not in the collection, return null

The test for this looks like this:

[

Test]
public void RetrieveABookmarkNotInCollection()
{
Assert.IsNull(collection[exampleDotComLabel]);
}

When I run this I get the following error:

BookmarkCollectionFixture.RetrieveABookmarkNotInCollection : System.Collections.Generic.KeyNotFoundException : The given key was not present in the dictionary.

Unfortunately it does not return null like I want it to. I guess I will have to write some code. I need to modify the Indexer to check to see if the label is in the collection. If not it should return null. Here's the code:

public Uri this[string label]
{
get
{
if (!dictionary.ContainsKey(label)) return null;

return dictionary[label];
}
}

I compile and run and the tests pass. Let's move on. The next post will address the following tests:

• Add a Bookmark with a null label, expect ArgumentNullException
• Add a Bookmark with a null URL, expect ArgumentNullException

Surveying the rest of the tests in the test list indicates that there is not much left so I should be able to finish up the task in the next couple of posts.

Comments

• Anonymous
  December 27, 2004
  This an extremely off-topic comment, but I have never understood why the library was written this way. In this code
  
  if (!dictionary.ContainsKey(label))
  return null;
  return dictionary[label];
  
  The lookup is actually performed twice for objects in the dictionary. What a horrible performance penalty! The STL and MFC approaches seems much more sane in that regard.
• Anonymous
  December 27, 2004
  Interesting read ;), I just came through.
  
  My question is, how many of us would rather write:
  
  if (!dictionary.ContainsKey(label))
  return null;
  else
  return dictionary[label];
  --
  
  It makes no real difference, but for me, it feels more 'right'.
  I want to return null if dictionary doesn't contain the key, else I want to return the value.
  
  Anybody else? :)
  
  RGab