App Checking for updates - ios

Question

I am creating a update method for in house enterprise apps. What I am trying to create is a class that I can quickly put in a app and it will check with the server if it needs to be updated. This is what I have so far, it checks correctly but its returning NO before it finishes the method.
In my checkUpdate.h
#interface checkForUpdate : NSObject
+ (BOOL)updateCheck;
#end
In my checkUpdate.m
#import "checkForUpdate.h"
#implementation checkForUpdate
BOOL needsUpdate
NSDictionary *versionDict;
#define kBgQueue dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
+ (BOOL)updateCheck {
NSString *urlStringVersion = [[NSString alloc] initWithFormat:#"http://URL/app_info?app=app"];
NSURL *urlVersion = [NSURL URLWithString:urlStringVersion];
dispatch_async(kBgQueue, ^{
NSData* data =[NSData dataWithContentsOfURL:urlVersion];
if (data){
NSError* error;
NSArray* json = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
if (json != nil && [json count] != 0) {
versionDict = [json objectAtIndex:0];
CGFloat serverVersion = [[versionDict valueForKey:#"version"]floatValue];
CGFloat appVersion = [[[[NSBundle mainBundle] infoDictionary] objectForKey:(NSString*)kCFBundleVersionKey] floatValue];
NSLog(#"Server Version %f",serverVersion);
NSLog(#"App Version %f",appVersion);
if ([versionDict count] != 0){
if (serverVersion > appVersion){
[[UIApplication sharedApplication] setApplicationIconBadgeNumber:1];
needsUpdate = YES;
}else{
[[UIApplication sharedApplication] setApplicationIconBadgeNumber:0];
needsUpdate = NO;
}
}
}
}
});
return needsUpdate;
}
#end
I call it like this
NSLog(#"Needs Update %#",[checkForUpdate checkForUpdateWithResponse] ? #"Yes":#"No");
This is my log
Needs Update No
Server Version 2.000000
App Version 1.000000
I'm not sure why it's returning NO before it even checks. I need it to be a asynchronous because the server that the app will check with is behind our firewall. So if the person is outside the firewall the app needs to continue when is can't reach the server. I'm I headed in the right direction, or is there a better way?

Answer 1

You are asynchronously checking for an update but expecting an immediate response by virtue of your method's design. You can re-engineer your method to something like the example below to notify a handler whenever the operation is complete:
Note: Unchecked and untested for errors; however, the lesson to be gleaned from the example is to use a callback of sorts:
UpdateChecker Class
typedef void (^onComplete)(BOOL requiresUpdate);
#interface UpdateChecker : NSObject
-(void)checkForUpdates:(onComplete)completionHandler;
#end
#implementation UpdateChecker
-(void)checkForUpdates:(onComplete)completionHandler
{
NSString *urlStringVersion = [[NSString alloc] initWithFormat:#"http://URL/app_info?app=app"];
NSURL *urlVersion = [NSURL URLWithString:urlStringVersion];
dispatch_block_t executionBlock =
^{
/*
Your update checking script here
(Use the same logic you are currently using to retrieve the data using the url)
*/
NSData* data = [NSData dataWithContentsOfURL:urlVersion];
BOOL requiresUpdate = NO;
if (data)
{
...
...
...
requiresUpdate = ...; //<-whatever your outcome
}
//Then when completed, notify the handler (this is our callback)
//Note: I typically call the handler on the main thread, but is not required.
//Suit to taste.
dispatch_async(dispatch_get_main_queue(),
^{
if (completionHandler!=NULL)
completionHandler(requiresUpdate);
});
};
dispatch_async(kBgQueue, executionBlock);
}
#end
This is what it would look when you use UpdateChecker to check for updates throughout your app
UpdateChecker *checker = [UpdateChecker alloc] init];
[checker checkForUpdates:^(BOOL requiresUpdate)
{
if (requiresUpdate)
{
//Do something if your app requires update
[[UIApplication sharedApplication] setApplicationIconBadgeNumber:1];
}
else
[[UIApplication sharedApplication] setApplicationIconBadgeNumber:0];
}];

Answer 2

Since dispatch_async is non-blocking, your method returns before your update information has returned (does the dispatch and continues). As needsUpdate defaults to NO, that's what you'll see. You can see this in your log timing - the "Needs Update No" shows up before the server and app versions.
You need some sort of callback (a delegate method or second dispatch_async for example) to ensure you get the correct result, or you need to block. I recommend looking into NSURLConnection, and sendAsynchronousRequest:queue:completionHandler: - it will execute the completion handler on completion, where you can have whatever code you need for handling the update.