This example uses a couple of C# 4.0 features: it uses the new dynamic keyword for runtime binding to members. It also uses the support for optional arguments. The Open and Close methods take 16 and 3 arguments, respectively, and as you can see from Example 1-3, you need to provide all of them in C# 3.0. But Example 1-4 has only provided values for the arguments it wants to set to something other than the default. Besides using these two new features, a project containing this code would usually be built using a third new interop feature called no-PIA. There s nothing to see in the preceding example, because when you enable no-PIA in a C# project, you do not need to modify your code no-PIA is essentially a deployment feature. In C# 3.0, you had to install special support libraries called primary interop assemblies (PIAs) on the target machine to be able to use COM APIs such as Office automation, but in C# 4.0 you no longer have to do this. You still need these PIAs on your development machine, but the C# compiler can extract the information your code requires, and copy it into your application. This saves you from deploying PIAs to the target machine, hence the name, no-PIA . While these new language features are particularly well suited to COM automation interop scenarios, they can be used anywhere. (The no-PIA feature is narrower, but it s really part of the .NET runtime rather than a C# language feature.)

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Note The arc starts at 90 degrees because 0 degrees is considered to be the point to the right of the


In this chapter we provided a quick overview of the nature of the C# language, and we showed some of its strengths and how the latest version has evolved. There s one last benefit you should be aware of before we get into the details in the next chapter, and that s the sheer quantity of C# resources available on the Internet. When the .NET Framework first appeared, C# adoption took off much faster than the other .NET languages. Consequently, if you re searching for examples of how to get things done, or solutions to problems, C# is an excellent choice because it s so well represented in blogs, examples, tools, open source projects, and webcasts Microsoft s own documentation is pretty evenhanded between C# and VB.NET, but on the Web as a whole, you re far better served if you re a C# developer. So with that in mind, we ll now look at the fundamental elements of C# programs.

Figure 6-11. Editing the HTML for your <ErrorLayout> tag on your ScriptManager control As mentioned earlier, you can use the HTML editor to specify how you want this error box to appear. Figure 6-12 shows a customized version of the error template.

This demonstrates that there s clearly just the one piece of information here, no matter how many different object instances we may try to look at it through. But why might we want this kind of static, class-level data storage The principal use for class-level data is to enforce the reality that there is exactly one instance of some piece of data throughout the whole system. If you think about it, that s exactly what our miles-to-kilometers value is all about we only need one instance of that number for the whole system, so we declare it as const (which, as we ve already

path.moveTo( 120, 120 ); path.lineTo( 120, 40 ); path.arcTo( 40, 40, 160, 160, 90, 90 ); path.lineTo( 120, 120 );

seen, is like a special case of static). A similar pattern crops up in lots of places in the .NET Framework class library. For example, on a computer running Windows, there is a specific directory containing certain OS system files (typically C:\Windows \system32). The class library provides a class called Environment which offers, among other things, a SystemDirectory property that returns that location, and since there s only one such directory, this is a static property. Another common use for static is when we want to cache information that is expensive to calculate, or which is frequently reused by lots of different objects of the same type. To get a benefit when lots of objects use the common data, it needs to be available to all instances.

We can even apply the static keyword to a constructor. This lets us write a special constructor that only runs once for the whole class. We could add the constructor in Example 3-43 to our Plane class to illustrate this.

static Plane() { Console.WriteLine("Plane static constructor"); }

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