iOS中的多线程

Question

Need your help.

In my application, i want to implement a background process which keeps running continuously and downloads the updated data and stores it in document folder.

And my main thread should keep checking the document folder and display the updated data in view control.

The child thread should end once the view disappears. and start again once the view appears.

What is the best way to do it? NSThread or NSOperationQueue? What precautions are required? I also have to access few variables of the class. So is should be thread safe.

Thanks in advance.

Regards

Answer 1

If you do not need to update a progress bar or something in iOS5 there is one great API method + sendAsynchronousRequest:queue:completionHandler: that allows you to run async download as a block inside NSOperationQueue. If not you should look into third party libs such as ASIHTTP request or https://github.com/AFNetworking/AFNetworking (probably better the last one) or you need to build you own download manager, not a simple task

Answer 2

there are two ways to do it..

First: You use NSOperationQueue which is a bit bulkier as it is build on GCD but does have some extra features.

Second: You use GCD (grand central dispatch) looking at requirements I would say GCD seems fine as you can easily access any thread(main or background) this would be slightly quicker.

Answer 3

You can have a look at - (void)performSelectorInBackground:(SEL)aSelector withObject:(id)arg This method creates a new thread in your application, putting your application into multithreaded mode if it was not already. In your viewDidDisappear, you can stop the task when your view disappears

From Apple Docs. Apple encourages to investigate the alternative Mac OS X technologies for implementing concurrency. This is especially true if you are not already familiar with the design techniques needed to implement a threaded application. These alternative technologies simplify the amount of work you have to do to implement concurrent paths of execution and offer much better performance than traditional threads. https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Multithreading/AboutThreads/AboutThreads.html#//apple_ref/doc/uid/10000057i-CH6-SW2