References and Using Directives - Page 3
       by kirupa  |  20 July 2008

In the previous page, you applied the vague description of using directives and references by looking at a real example. While that should have given you some hands-on experience seeing these two topics in greater detail, there are some interesting tidbits that I did not cover, so let's do that on this page.

Dealing with Naming Conflicts
While not a very common situation, there will be times where you will find that the right combination of referenced assemblies and using directives contain types whose names are not unique.

One example is when you are using the OpenFileDialog class and have both Microsoft.Win32 and System.Windows.Forms types in your project:

Your OpenFileDialog text will be displayed again with the funny blue, squiggly underline. When you press F6 to Build, you will receive an error! The reason for the error can be seen in the Error List:

[ the Error List is a great way to find out what the error means ]

The error is stating that there is some ambiguity in which OpenFileDialog you want to use. Do you want to use the one found in System.Windows.Forms or do you want to use the one found in Microsoft.Win32?

Let's say we just want to use the one found in System.Windows.Forms. To resolve this error, right click on OpenFileDialog in your code, and from the menu that appears, click on the Resolve menu item:

You will see the fully qualified names for OpenFileDialog that you can use. Depending on which you select, your OpenFileDialog text will change to that of your selected name - which in our case will be System.Windows.Forms.OpenFileDialog:

Be sure to do this for all occurrences of OpenFileDialog that you currently have in the code. In my case, I have two such occurrences...both in my declaration as well as initialization.

You probably aren't happy with the extra clutter now in your code. Despite that, this is actually necessary because, while your code looks less elegant, it removes all ambiguity on which OpenFileDialog you really want to use.

If you happen to remove either the System.Windows.Forms or Microsoft.Win32 using directive, you would not have to deal with this problem at all. It is for those rare cases where these conflicts occur, that you will have to trod down this path.

Does Adding Extra References Increase File Size?
Each reference you add usually points to another project or an assembly. In either case, they contain a certain file size themselves. A common question, especially with Silverlight applications, is whether adding references causes the file size of your final output to increase.

The answer to that is yes. Any reference you add, it will get compressed into your XAP if the runtime does not already contain this reference. For example, in the previous page you added a reference to System.Xml.Linq. When I build, my XAP's size is around 60k. When I look into the XAP, notice what I see:

System.Xml.Linq is contained inside your XAP, and it is a whopping 57k in size! Even if I removed the one line of code containing my XDocument object declaration and the System.Xml.Linq using directive, building the project will still produce a XAP whose size is 60k.

Only by actually removing the reference to System.Xml.Linq will the XAP no longer contain the System.Xml.Linq assembly:

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