.NET/Java PDF, Tiff, Barcode SDK Library

Look at the variable declaration on the first line. The square brackets after string indicate that eventNames is not just a single string; it s an array of string values. These square brackets tie in with the syntax for accessing individual elements in the array. Example 7-2 prints the first and fifth items in the array. (So this will print out the text Swing Dancing at the South Bank , followed by Stompin at the 100 Club .)

Summary

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Combining the knowledge of what a plugin interface is and what the filter plugin needs to do, you get something similar to the FilterInterface class shown in Listing 11-15 The name method returns the name of the filter, and the filter method filters the given QImage and returns the filtered result The names are clear, and it is easy to understand how things are supposed to work Listing 11-15 The ImageFilter interface class class FilterInterface { public: virtual QString name() const = 0; virtual QImage filter( const QImage &image ) const = 0; }; Before this class can be used as a plugin interface, you must tell Qt that it is an interface by using the lines shown in Listing 11-16 The first argument is the class involved; the second is an identifier string that must be unique for the interface Listing 11-16.

Console.WriteLine(eventNames[0]); Console.WriteLine(eventNames[4]);

The number inside the square brackets is called the index, and as you can see, C# starts counting array elements from zero. As you may recall from 2, the index says how far into the array we d like C# to look to access the very first element, we don t have to go any distance into the array at all, so its index is 0. Likewise, an index of 4 jumps past the first four items to arrive at the fifth. To modify an array element you just put the same syntax on the lefthand side of an assignment. For example, noticing that I got one of the event names slightly wrong, I can update it, like so:

eventNames[1] = "Saturday Night Swing Club";

Declaring the ImageFilter as being a plugin interface to Qt Q_DECLARE_INTERFACE( FilterInterface, "sethelinsCustomPluginFilterInterface/01" ) When the interface has been defined, the development can be split into two parts: the plugins and the application (the two sides of the interface)..

While you can change any element of an array like this, the number of elements is fixed for the lifetime of the array. (As we ll see later, this limitation is less drastic than it first sounds.)

If you try to use too high an index or a negative index when accessing an array element, the code will throw an IndexOutOfRangeException. Since elements are numbered from zero, the highest acceptable index is one less than the number of elements. For example, eventNames[4] is the last item in our five-item array, so trying to read or write eventNames[5] would throw an exception. The .NET Framework supports arrays whose first element is numbered from something other than zero. This is to support languages such as Visual Basic that have historically offered such a construct. However, you cannot use such arrays with the C# index syntax shown here you would need to use the Array class s GetValue and SetValue helper methods to use such an array.

Since the size of an array is fixed at the moment it is constructed, let s look at the construction process in more detail.

In this chapter, you got a brief history lesson on the methodologies for building user interfaces to servers that process your data and on the constantly swinging pendulum from thin client to fat client. You were brought up to date on what the newest trend in this development is web-based thin clients with rich functionality thanks to the asynchrony delivered by the XMLHttpRequest object. This object is the core of Ajax, and in this chapter you built a simple demonstration that used it. This example was straightforward and barely scratched the surface of what you can do with Ajax; however, it demonstrated one of the drawbacks of using this methodology, namely, that it is heavy on the scripting. JavaScript, although powerful, is difficult and onerous to debug and manage when compared to languages such as C#, VB .NET, and Java. As such, the application benefits you receive by using an Ajax approach may be nullified by the application development getting bogged down in thousands (or more) lines of JavaScript.

There are two ways you can create a new array in C#. Example 7-1 showed the most straightforward approach the array variable declaration was followed by a list of the