The Importance ofReachability
Marc WeilCTO, CloudMine
Wireless connections aren’t perfect
Defensive Programming
Let’s look at a quick example
- (void)doLoad { NSURLRequest *req = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://google.com"]]; NSHTTPURLResponse *response = [[NSHTTPURLResponse alloc] init]; NSData *responseBody = [NSURLConnection sendSynchronousRequest:req returningResponse:&response error:NULL]; // responseBody contains the response body}
Why is this naive?
• Potentially blocks UI thread• No error handling• What happens if there’s no network connection?
- (void)doLoad { NSURLRequest *req = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://google.com"]]; [NSURLConnection sendAsynchronousRequest:req queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *resp, NSData *body, NSError *err) { if (!err) { NSLog(@"Success!"); // body argument contains response body } else { NSLog(@"Error!"); } }];}
Why is this still naive?
• Potentially blocks UI thread• No error handling• What happens if there’s no network connection?
- (void)doLoad { NSURLRequest *req = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://google.com"]]; [NSURLConnection sendAsynchronousRequest:req queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *resp, NSData *body, NSError *err) { if (!err) { NSLog(@"Success!"); // body argument contains response body } else { NSLog(@"Error!"); } }];}
Why is this still naive?
• Potentially blocks UI thread• No error handling• What happens if there’s no network connection?
Queues are your best friend
Internet
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
When everything is dandy...
Request generator HTTP
Constantflow(th
is is
the q
ueue
)
Internet
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
When everything is not so dandy...
Request generator HTTP
Haltedflow
HTTP
HTTP
(this
is th
e que
ue)
How can I do this in code?
(apologies to Android devs)
Three components:
1. NSOperationQueue2. NSOperation3. Reachability
NSOperationQueue *queue = [[NSOperationQueue alloc] init]; [queue addOperationWithBlock:^{ NSURLRequest *req = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://google.com"]]; NSHTTPURLResponse *response = [[NSHTTPURLResponse alloc] init]; NSData *responseBody = [NSURLConnection sendSynchronousRequest:req returningResponse:&response error:NULL]; }];
NSOperationQueue *queue = [[NSOperationQueue alloc] init]; [queue addOperationWithBlock:^{ NSURLRequest *req = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://google.com"]]; NSHTTPURLResponse *response = [[NSHTTPURLResponse alloc] init]; NSData *responseBody = [NSURLConnection sendSynchronousRequest:req returningResponse:&response error:NULL]; }];
This is a convenience method that creates anNSBlockOperation under the hood.
Internet
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTPRequest
generator HTTP
Constantflow
(NSOperations)NSOperationQueue
NSOperation
What about Reachability?
Everything is contained inSystemConfiguration.framework
But don’t use that directly... it’s terrible
https://github.com/tonymillion/Reachability
(love abstraction!)
// allocate a reachability object Reachability* reach = [Reachability reachabilityWithHostname:@"www.google.com"]; reach.reachableOnWWAN = YES; // set the blocks reach.reachableBlock = ^(Reachability *reach) { queue.suspended = NO; }; reach.unreachableBlock = ^(Reachability *reach) { queue.suspended = YES; }; // start the notifier which will cause the reachability object to retain itself! [reach startNotifier];
(example from readme on GitHub)
https://github.com/AFNetworking/AFNetworking
Bringing out the big guns...(thanks Gowalla!!! <3)
POW!
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
One more pet peeve....are apps that don’t do this
https://github.com/tonymillion/Reachability
https://github.com/AFNetworking/AFNetworking
Resources
http://developer.apple.com/library/ios/#samplecode/Reachability/Introduction/Intro.html
Contact Mee: [email protected]: @marcweil
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