Simple .NET/ASP.NET PDF document editor web control SDK

Some arrays will be sparser than others, and there will inevitably come a point of insufficient sparseness at which this dictionary-based approach will end up being less efficient than simply using a large array. It s hard to predict where the dividing line between the two techniques will fall, as it will depend on factors such as the type and quantity of data involved, and the range of index values. As with any implementation choice made on the grounds of efficiency, you should compare the performance against the simpler approach to find out whether you re getting the benefit you hoped for.

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Figure 1-4. Request/response architecture of graphical user interface (GUI) application talking to mainframe

The examples we ve seen so far have all used the Dictionary type defined in the System.Collections.Generic namespace. But that s not the only dictionary. As we saw a couple of chapters ago, the IEnumerable<T> type lets us write polymorphic code that can work with any sequential collection class. We can do the same with a dictionary the .NET Framework class library defines an interface called IDictionary<TKey, TValue>, which is reproduced in Example 9-8.

namespace System.Collections.Generic { public interface IDictionary<TKey, TValue> : ICollection<KeyValuePair<TKey, TValue>>, IEnumerable<KeyValuePair<TKey, TValue>>, IEnumerable { void bool bool bool Add(TKey key, TValue value); ContainsKey(TKey key); Remove(TKey key); TryGetValue(TKey key, out TValue value);

}

requirements differ depending on how Qt is configured, so you should study the reference documentation if you run into problems.

}

TValue this[TKey key] { get; set; } ICollection<TKey> Keys { get; } ICollection<TValue> Values { get; }

You can see the indexer TValue this[TKey] and the TryGetValue method that we already looked at. But as you can see, dictionaries also implement other useful standard features. The Add method adds a new entry to the dictionary. This might seem redundant because you can add new entries with the indexer, but the difference is that the indexer will happily overwrite an existing value. But if you call Add, you are declaring that you believe this to be a brand-new entry, so the method will throw an exception if the dictionary already contained a value for the specified key. There are members for helping you discover what s already in the dictionary you can get a list of all the keys and values from the Keys and Values properties. Both of these implement ICollection<T>, which is a specialized version of IEnumerable<T> that adds in useful members such as Count, Contains, and CopyTo. Notice also that IDictionary<TKey, TValue> derives from IEnumerable<KeyPair Value<TKey, TValue>>. This means it s possible to enumerate through the contents of a dictionary with a foreach loop. The KeyPairValue<TKey, TValue> items returned by the enumeration just package the key and associated value into a single struct. We could

When the file has been downloaded, the procedure goes like this: unpack, configure, and compile Let s go through these steps one by one The easiest way is to work from the command prompt To unpack the file, download it, place it in a directory, and go there in your command shell Then type something like this (put x11 or mac in place of edition and use the version that you have downloaded): tar xvfz qt-edition-opensource-src-versiontargz This code extracts the file archive to a folder named qt-edition-opensource-src-version Use the cd command to enter that directory: cd qt-edition-opensource-src-version Before building Qt, you need to configure it using the configure script and its options Run the script like this: /configure options There are lots of options to choose from The best place to start is to use -help, which shows you a list of the available options.

add the method in Example 9-9 to the class in Example 9-7, in order to print out just those elements with a nondefault value.

With this steadily exponential increase in computing power at the desktop, applications became more sophisticated, complex, and functional than anything before on centralized mainframe supercomputers. Full GUIs soon became the norm. Microsoft Windows appeared, following Apple, Atari, and other GUI-focused computers. Soon after, office productivity applications exploded onto the scene; and as people began using these applications daily, they required even faster and more sophisticated platforms, and the client continued to evolve exponentially.

public void ShowArrayContents() { foreach (var item in nonEmptyValues) { Console.WriteLine("Key: '{0}', Value: '{1}'", item.Key, item.Value); } }

Remember, the presence of IEnumerable<T> is all that LINQ to Objects needs, so we can use dictionaries with LINQ.