reachability in mobile app development

The Importance ofReachability

Marc WeilCTO, CloudMine

marc@cloudmine.me

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

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When everything is not so dandy...

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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.

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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: marc@cloudmine.met: @marcweil