.NET/Java PDF, Tiff, Barcode SDK Library

Qt classes emit signals when they are stimulated by programmatic calls or user interaction. Because signals and slots are key components of Qt applications, they must not be left out during testing. You can use the QSignalSpy class to listen to signals without connecting to them. A signal spy is hooked up to listen to a certain signal from a certain object. The spy object then records the argument values for each signal caught. Listing 16-21 shows the data-driven testKeys method extended with signal listening capabilities. (The original implementation slot was shown in Listing 16-19.) The highlighted lines in the listing show major additions to the slot. Looking at the changes from the top down, the first line creates a QSignalSpy object for monitoring the valueChanged(int) signal emitted from the spinBox object. The signal spy is created after the spin box has been set up with the start value to avoid catching a signal by mistake.

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This example presumes that MyDataSource is some data source class that provides a queryable collection containing a list of buildings. Since this information would typically be stored in a database, you would probably use a database LINQ provider such

as LINQ to Entities or LINQ to SQL. The nature of the source doesn t greatly matter, though the mechanism for extracting the resources into a dictionary object are the same in any case. The ToDictionary operator needs to be told how to extract the key from each item in the sequence. Here we ve provided a lambda expression that retrieves the ID property again, this property would probably be generated by a database mapping tool such as the ones provided by the Entity Framework or LINQ to SQL. (We will be looking at data access technologies in a later chapter.) This example supplies a second lambda, which chooses the value here we pick the Name property. This second lambda is optional if you don t provide it, ToDictionary will just use the entire source item from the stream as the value so in this example, leaving out the second lambda would cause ToDictionary to return an IDictionary<int, Building> (where Building is whatever type of object MyDataSource.Buildings provides). The code in Example 9-11 produces the same result as this:

var buildingIdToNameMap = new Dictionary<int, string>(); foreach (var building in MyDataSource.Buildings) { buildingIdToNameMap.Add(building.ID, building.Name); }

It s important to note that the more sophisticated applications were disconnected applications Office productivity suites, desktop-publishing applications, games, and the like, were all distributed, installed, and run on the client via a fixed medium such as a floppy disk or CD In other words, they weren t connected in any way The other breed of application, which was evolving much more slowly, was the connected application, where a graphical front end wrapped a basic, text-based communication back end for online applications such as email CompuServe was one of the largest online providers, and despite the innovative abstraction of its simple back end to make for a more user-centric, graphical experience along the lines of the heavy desktop applications, its underlying old-school model was still apparent.

HashSet<T> is a collection of distinct values. If you add the same value twice, it will ignore the second add, allowing any given value to be added only once. You could use

Note This test checks only one signal. In real life, you would include the valueChanged(QString)

this to ensure uniqueness for example, imagine an online chat server. If you wanted to make sure that usernames are unique, you could maintain a HashSet<string> of usernames used so far, and check that a new user s chosen name isn t already in use by calling the hash set s Contains method.

You might notice that List<T> offers a Contains method, and so with a little extra code, you could implement a uniqueness check using List<T>. However, HashSet<T> uses the same hash-code-based fast lookup as a dictionary, so HashSet<T> will be faster for large sets than List<T>.

nothing useful in the value as a way of getting fast hash-code-based uniqueness testing. .NET 4 adds SortedSet<T>, which is very similar to HashSet<T>, but adds the feature that if you iterate through the items in the set, they will come out in order. (You can provide an IComparer<T> to define the required order, or you can use self-ordering types.) Obviously, you could achieve the same effect by applying the OrderBy LINQ operator to a HashSet<T>, but SortedSet<T> sorts the items as they are added, meaning that they re already sorted by the time you want to iterate over them.