A 10 minute talk I gave at the API Strategy Conference in NYC on the importance of using reachability detection in conjunction with message queues when communicating with web services from mobile devices. Includes specific examples for iOS.

1. The Importance of
Reachability
Marc Weil
CTO, CloudMine
marc@cloudmine.me

2. Wireless connections aren’t perfect

3. Defensive Programming

4. Let’s look at a quick example

5. - (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?

6. - (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?

7. - (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?

8. Queues are your best friend

9. Internet
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10. Internet
When everything is not so
dandy...
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11. How can I do this in code?
(apologies to Android devs)

12. Three components:
1. NSOperationQueue
2. NSOperation
3. Reachability

13. 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];
}];

14. 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 an
NSBlockOperation under the hood.

15. Internet
HT
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generator HTTP HTTP

16. What about Reachability?

17. Everything is contained in
SystemConfiguration.framework

18. But don’t use that directly... it’s terrible

19. https://github.com/tonymillion/Reachability
(love abstraction!)

20. // 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)

21. !
POW
Bringing out the big guns...
https://github.com/AFNetworking/AFNetworking
(th
an
k sG
ow
all
a!!
<3!
)

22. One more pet peeve....
are apps that don’t do this
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];

23. Resources
https://github.com/tonymillion/Reachability
https://github.com/AFNetworking/AFNetworking
http://developer.apple.com/library/ios/#samplecode/Reachability/
Introduction/Intro.html
Contact Me
e: marc@cloudmine.me
t: @marcweil