System.Net和没有System.Net之间的区别

Question

What is the difference between adding System.Net like this:

 CookieContainer globalcontainer = new System.Net.CookieContainer();

and using the class without the namespace in the declaration

 CookieContainer globalcontainer = new CookieContainer();

Which is better in efficiency?

Answer 1

Neither is more efficient, one is explicity specifying the namespace, the other is implicitly.

At the top of your .cs file, the using directives import namespaces, meaning that types in those namespaces don't need the fully qualified path to be recognised in the code

eg

List<T> appears in System.Collections.Generic ... without the using directive for this namespace you must use the fully qualified name:

System.Collections.Generic.List<int> someList;

Whereas with it, you don't

using System.Collections.Generic;

List<int> someList;

Sometimes there can be namespace collisions - imagine the following scenario:

Some.Namespace.Task
Some.Othernamespace.Task

If you import both namespaces:

using Some.Namespace;
using Some.Othernamespace;

Task someTask; // <--- this line will cause a compile time error

The compiler doesn't know which Task you want, the one from Some.Namespace or the one from Some.Othernamespace - in this case you need to be specific and supply the full namespace (or use an alias)

Hope this helps

Read all about namespaces here:

http://msdn.microsoft.com/en-gb/library/z2kcy19k(v=vs.80).aspx

Answer 2

In run-time the two will often be the same.

For readability, I often prefer not using the namespace in the same statement (put it in using directive on the top of the file) because it usually saves me space, allowing my lines not to go too long, it's admittedly a small benefit.

These are times when I do include the namespace:

• When I know the class name is likely to be misunderstood, sometimes there are types used in different namespaces in .NET, and I'd like the reader of the code to get what I mean faster

• When it's the only call from this namespace, sometimes I include the namespace explicitly.

• If I'm importing multiple namespaces that contain the same type. this one is obvious though.

So, the answer, as good or bad as this may sound, is "it depends". Whatever makes the code more readable in less time wins.

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