C# – Using Ext JS in ASP.NET

There is actually a (subtle) difference between the two. Imagine you have the following code in File1.cs:

// File1.cs
using System;
namespace Outer.Inner
{
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now imagine that someone adds another file (File2.cs) to the project that looks like this:

// File2.cs
namespace Outer
{
    class Math
    {
    }
}

The compiler searches Outer before looking at those using directives outside the namespace, so it finds Outer.Math instead of System.Math. Unfortunately (or perhaps fortunately?), Outer.Math has no PI member, so File1 is now broken.

This changes if you put the using inside your namespace declaration, as follows:

// File1b.cs
namespace Outer.Inner
{
    using System;
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now the compiler searches System before searching Outer, finds System.Math, and all is well.

Some would argue that Math might be a bad name for a user-defined class, since there's already one in System; the point here is just that there is a difference, and it affects the maintainability of your code.

It's also interesting to note what happens if Foo is in namespace Outer, rather than Outer.Inner. In that case, adding Outer.Math in File2 breaks File1 regardless of where the using goes. This implies that the compiler searches the innermost enclosing namespace before it looks at any using directive.

Nor sure if it is the quickest approach, but all I did (as well as another developer that was working with me) was review the ExtJS documentation and samples gallery (and viewing their source).

One big issue to watch out for when using ExtJS with ASP.NET is that when using BorderLayout you will go crazy trying to figure out why Postbacks no longer work. There is a workaround though.

Another ASP.NET gotcha is that if you use ExtJS to talk with ASP.NET web services (or WCF) you have to do some special things to get it to work (adorn your webmethod with special attributes, or add some things to web.config, etc).

Those were the only two gotchas I can recall, other than just learning and getting the hang of ExtJS itself.