Multi-tasking prevents apps from freezing. In most programming languages, achieving this is a bit tricky, but the NSOperationQueue class in iOS makes it easy!
This tutorial will demonstrate how to use the NSOperationQueue class. An NSOperationQueue object is a queue that handles objects of the NSOperation class type. An NSOperation object, simply phrased, represents a single task, including both the data and the code related to the task. The NSOperationQueue handles and manages the execution of all the NSOperation objects (the tasks) that have been added to it. The execution takes place with the main thread of the application. When an NSOperation object is added to the queue it is executed immediately and it does not leave the queue until it is finished.