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

Sometimes the interesting thing is not mapping a value to a key, but remembering which keys are valid. In this situation, you can use the QSet class. A set is a hash without the value, so there must be a qHash function and a == operator for the keys. Also, the order of the keys is arbitrary. Listing 1-25 shows that you populate a set by using the same operator as when you populate a list. Farther down, the two access methods can be seen. You can either access the keys by using an iterator or you can call contains to see whether the key is a part of the set. Listing 1-25. Populating a QSet; then showing the keys and testing for the key "FORTRAN" QSet<QString> set; set << "Ada" << "C++" << "Ruby"; for( QSet<QString>::ConstIterator ii = set.begin(); ii != set.end(); ++ii ) qDebug() << *ii; if( set.contains( "FORTRAN" ) ) qDebug() << "FORTRAN is in the set."; else qDebug() << "FORTRAN is out.";

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CalendarEvent newEvent = new CalendarEvent { Title = "Dean Collins Shim Sham Lesson", StartTime = new DateTimeOffset (2009, 7, 14, 19, 15, 00, TimeSpan.Zero), Duration = TimeSpan.FromHours(1) }; events.Add(newEvent);

This appends the element to the end of the list. If you want to put the new element somewhere other than at the end, you can use Insert:

events.Insert(2, newEvent);

to wait until it is unlocked by the current holder before it can lock it It is said that the method blocks until it can be completed The lock and unlock operations are atomic, which means that they are treated as single undivisable operations that can t be interrupted during execution This is important because locking a mutex is a two-step process First the thread checks that the mutex isn t locked; then it marks it as locked If the first thread would be interrupted after having checked, and the second thread then checks and locks the mutex, the first thread will think that the mutex is unlocked when it resumes It will then mark an already locked mutex as locked, which creates a situation in which two threads think that they have locked the mutex.

The first argument indicates the index at which you d like the new item to appear any items at or after this index will be moved down to make space. You can also remove items, either by index, using the RemoveAt method, or by passing the value you d like to remove to the Remove method (which will remove the first element it finds that contains the specified value).

List<T> does not have a Length property, and instead offers a Count. This may seem like pointless inconsistency with arrays, but there s a reason. An array s Length property is guaranteed not to change. A List<T> cannot make that guarantee, and so the behavior of its Count property is necessarily different from an array s Length. The use of different names signals the fact that the semantics are subtly different.

makes it much easier to concatenate lists remember that with arrays we ended up writing the CombineEvents method in Example 7-18 to concatenate a couple of arrays. But with lists, it becomes as simple as the code shown in Example 7-23.

events1.AddRange(events2);

Because the locking operation is atomic, the first thread will not be interrupted between the check and the locking, thus the second thread will check and find a locked mutex In Qt, mutexes are implemented by the QMutex class The methods for locking and unlocking are called lock and unlock Another method, tryLock, locks the mutex only if it is not owned by another thread By altering the application from Listings 12-1, 12-2, and 12-3, you can make sure that the "Foo" and "Bar" texts always appear in the same order Listing 12-5 shows the modified run method The added lines of code have been highlighted The added lines make sure that each thread holds the lock while printing the text and sleeping During this time, the other thread also calls lock and then blocks until the current holder unlocks the mutex.

The control doesn t support any methods or events. It is simply used to get a better understanding of a specific column, returning its name, type, and default value.

The one possible downside of List<T> is that this kind of operation modifies the first list. Example 7-18 built a brand-new array, leaving the two input arrays unmodified, so if any code happened still to be using those original arrays, it would carry on working. But Example 7-23 modifies the first list by adding in the events from the second list. You would need to be confident that nothing in your code was relying on the first list containing only its original content. Of course, you could always build a brand-new new List<T> from the contents of two existing lists. (There are various ways to do this, but one straightforward approach is to construct a new List<T> and then call AddRange twice, once for each list.)

You access elements in a List<T> with exactly the same syntax as for an array. For example:

Console.WriteLine("List element: " + events[2].Title);