Try this:
When he is being aggressive with a toy or food........ make sure you have something MUCH better than he does..... like a tiny piece of steak or chicken. Try to make a "trade" with him. Let him know that if he lets you HAVE his toy or food... something good will happen (he will get the much better treat). Also say the word "trade" when you do this.
......... this will make YOU in command (you have the better treat) and the dog will want to please you to get it........ and Yorkies LOVE to please!!! ( I know that my two are so proud when they do their tricks for me.... and of course they are rewarded with praise... and a treat
)