.NET/ASP.NET/C#/VB.NET PDF Document SDK

working their way through the same collection at the same time, without all of them needing to be in the same place. This can be useful in multithreaded applications (although as we ll see in a later chapter, you have to be extremely careful about letting multiple threads use the same data structure simultaneously).

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The work of the producer is performed in the run method shown in Listing 12-19 The for loop iterates over the text and then places the QChar objects on the buffer one by one, synchronizing with the consumer, as described previously When the entire text has been sent, the atEnd flag is set to true so the consumer knows that the entire text has been sent Listing 12-19 The run method of the producer class void TextProducer::run() { for( int i=0; i<m_textlength(); ++i ) { freeSpaceacquire(); buffer[ i % bufferSize ] = m_text[ i ]; if( i == m_textlength()-1 ) atEnd = true; availableDatarelease(); } } The consuming thread reads in the same order that it is filled from index 0 to bufferSize-1 and then starting from 0 again Before reading, it attempts to acquire from the availableData semaphore.

Some enumerable collections, such as List<T>, can be modified. (.NET defines an IList<T> interface to represent the abstract idea of a modifiable, ordered collection. List<T> is just one implementation IList<T>.) You should avoid modifying a collection while you re in the process of iterating through it. For example, do not call Add on a List<T> in the middle of a foreach loop that uses that list. List<T> detects when this happens, and throws an exception. Note that unlike IList<T>, IEnumerable<T> does not provide any methods for modifying the sequence. While this provides less flexibility to the consumer of a sequence, it broadens the range of data that can be wrapped as an IEnumerable<T>. For some sources of data it doesn t make sense to provide consumers of that data with the ability to reorder it.

The Sys.UI.Data.ListView control complements the ItemView control. This allows you to view a range of records that are selected by the bound DataSource control. The control exposes the properties shown in Table 8-15. Table 8-15. ListView Properties

These interfaces make it possible to write a function that uses a collection without having any idea of the collection s real type you only need to know what type of elements it contains. We could rewrite Example 7-3 so that it works with any IEnumer able<string> rather than just an array of strings, as shown in Example 7-30.

static string[] AddNumbers(IEnumerable<string> names) { List<string> numberedNames = new List<string>(); using (IEnumerator<string> enumerator = names.GetEnumerator()) { int i = 0; while (enumerator.MoveNext()) { string currentName = enumerator.Current; numberedNames.Add(string.Format("{0}: {1}", i, currentName)); i += 1; } } return numberedNames.ToArray();

When a character has been read from the buffer, it then releases to the freeSpace semaphore because that index of the buffer can be reused by the producer The consumer class, which is called TextConsumer, implements only a run method (see Listing 12-20) The implementation of the run method is straightforward..

}

Since List<T> and arrays both implement IEnumerable<T>, this modified code in Example 7-30 will now work with List<string>, as well as arrays, or any other collection class that implements IEnumerable<string>. For more information on the subtleties of type compatibility and enumerations, see the sidebar on the next page.

Suppose you ve written a function that uses an enumeration of elements of some base type, perhaps an IEnumerable<FirefighterBase>. ( 4 defined FirefighterBase as a base class of various types representing firefighters.) For example:

static void ShowNames(IEnumerable<FirefighterBase> people) { foreach (FirefighterBase person in people) { Console.WriteLine(person.Name); } }