ASP.NET Web PDF Document Viewer/Editor Control Library

If a file is selected in the directory contents list, the Get File button is enabled. Clicking this button causes the getClicked slot to be called. The slot shown in Listing 14-10 implements a three-stage operation. First, it asks what file name to use to save the file being downloaded by using QFileDialog::getSaveFileName. If it gets a valid file name, it attempts to create a QFile object for it and opens it for writing. If that succeeds, it calls the get method of the QFtp object, passing the file name and QFile object as arguments. The slot also disables all buttons before calling get. After it has called get, it updates the status text. The get method starts a download operation of the specified file. The resulting data is saved to the given QIODevice (superclass of QFile). While a QFtp object performs a download, the progress is reported through a series of dataTransferProgress signals connected to the ftpProgress slot (see Listing 14-10 after the source code for the getClicked slot). The arguments given to ftpProgress do not necessarily represent bytes; they show only their relative size. In some situations, the size of the file being downloaded is unknown. Then the total argument is zero. If the size is known, the slot updates the status label to show the progress.

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As you would expect, this will throw an InvalidCastException if it discovers any elements in the collection that are not of the type you said. But be aware that like most LINQ operators, Cast uses deferred execution it casts the elements one at a time as they are requested, so any mismatch will not be discovered at the point at which you call Cast. The exception will be thrown at the point at which you reach the first nonmatching item while enumerating the query.

Summary

Number animations are similar to length animations but don t append the text to the end and instead offer the facility to use fractional values. In this case, you can animate through a range of values that aren t limited to whole numbers. Discrete animations also allow you to change the value of a control s property automatically through a predefined range. You could, for example, automatically cycle the contents of a text field through the values a through z by specifying these as a list to a property on the animation and then triggering that animation. From this chapter you have gleaned some great new tools to make your UIs more sophisticated and easy to use for your users. In the next chapter, you will look at another value-added client-side library that Atlas gives you the Mapping library. This library allows you to instantly and easily add mapping and geocoding functionality to your applications that will update in an asynchronous, Ajax-like manner.

LINQ provides a convenient syntax for performing common operations on collections of data. The query expression syntax is reminiscent of database query languages, and can be used in conjunction with databases, as later chapters will show. But these queries are frequently used on objects in memory. The compiler transforms the query syntax into a series of method calls, meaning that the choice of LINQ implementation is determined by context you can write your own custom LINQ provider, or use a builtin provider such as LINQ to Objects, LINQ to SQL, or LINQ to XML. All providers implement standard operators methods with well-known names and signatures that implement various common query features. The features include filtering, sorting, grouping, and the ability to transform data through a projection. You can also perform test and aggregation operations across entire sets. Queries can be composed most operators output can be used as input to other operators. LINQ uses a functional style to maximize the flexibility of composition.

to upload a file, you can listen to the same signal as when using get to download when you want to show progress.

In the preceding two chapters we saw how to store information in arrays and lists, and how to sort, search, and process that information using LINQ. Important as sequential lists and rectangular arrays are, they don t accommodate every possible requirement you could have for storing and structuring data. So in this final chapter on working with collections, we ll look at some of the other collection classes offered by the .NET Framework.

You can think of a stream like one of those old-fashioned news ticker tapes. To write data onto the tape, the bytes (or characters) in the file are typed out, one at a time, on the continuous stream of tape. We can then wind the tape back to the beginning, and start reading it back, character by character, until either we stop or we run off the end of the tape. Or we could give the tape to someone else, and she could do the same. Or we could read, say, 1,000 characters off the tape, and copy them onto another tape which we give to someone to work on, then read the next 1,000, and so on, until we run out of characters.