Online and offline support for RestKit iOS applications

I am wanting to use RestKit for an application that needs to work both while on and offline.

I may be misunderstanding how RestKit works, but I thought that this was (fairly) easy to implement.

In a scratch test iOS app I set things up as follows:

// setup the client
NSString* URL = @"http://10.211.55.5:3000/api";
RKClient* client = [RKClient clientWithBaseURL:URL];
client.username = @"me@email.com";
client.password = @"password";

// setup caching
client.cachePolicy = RKRequestCachePolicyLoadIfOffline | RKRequestCachePolicyLoadOnError | RKRequestCachePolicyTimeout;
client.requestCache.storagePolicy = RKRequestCacheStoragePolicyPermanently;

// setup managed object store
RKObjectManager* objectManager = [RKObjectManager objectManagerWithBaseURL:URL];
RKManagedObjectStore* objectStore = [RKManagedObjectStore   objectStoreWithStoreFilename:@"RestKitCoreDataTest.sqlite"];

// connect my cache implementation
MyCache* cache = [[MyCache alloc] init];
objectStore.managedObjectCache = cache;
objectManager.objectStore = objectStore;

// setup mapping    
RKManagedObjectMapping* userMapping = [RKManagedObjectMapping mappingForClass:[User class]];
[userMapping mapKeyPath:@"id" toAttribute:@"identifier"];
[userMapping mapKeyPath:@"email" toAttribute:@"email"];
[userMapping mapKeyPath:@"firstname" toAttribute:@"firstname"];
[userMapping mapKeyPath:@"surname" toAttribute:@"surname"];
userMapping.primaryKeyAttribute = @"identifier";
[objectManager.mappingProvider setMapping:userMapping forKeyPath:@""];

// setup routes
RKObjectRouter* router = [objectManager router];
[router routeClass:[User class] toResourcePath:@"/users/:identifier"];

The User object is implemented as required for CoreData support:

@interface User : NSManagedObject

@property (nonatomic, retain) NSNumber * identifier;
@property (nonatomic, retain) NSString * email;
@property (nonatomic, retain) NSString * firstname;
@property (nonatomic, retain) NSString * surname;

@end

@implementation User

@dynamic identifier;
@dynamic email;
@dynamic firstname;
@dynamic surname;

@end

Here is MyCache. Note that I am not bothering to check resourcePath since this is just for trying things out, and I have one path anyway.

@implementation MyCache
- (NSArray*)fetchRequestsForResourcePath:(NSString*)resourcePath
{
    NSFetchRequest* fetchRequest = [User fetchRequest];
    return [NSArray arrayWithObject:fetchRequest];
}

-(BOOL)shouldDeleteOrphanedObject:(NSManagedObject *)managedObject
{
    return true;
}
@end

I then make a call to the server to get the user with id 123, at the path "/api/users/123":

User* user = [User object];
user.identifier = [NSNumber numberWithInt:123];
RKObjectManager* manager = [RKObjectManager sharedManager];
[manager getObject:user delegate:self];

This works fine. But, when I then disconnect the wifi on my Mac, the above code does not retrieve the user from the sqlite database.

I get the following error instead in the delegate's objectLoader:didFailWithError:

2012-03-01 11:44:09.402 RestKitCoreDataTest[1989:fb03] error: Error Domain=NSURLErrorDomain Code=-1001 "The request timed out." UserInfo=0x6b89aa0 {NSErrorFailingURLStringKey=http://10.211.55.5:3000/api/users/123, NSErrorFailingURLKey=http://10.211.55.5:3000/api/users/123, NSLocalizedDescription=The request timed out., NSUnderlyingError=0x6b81ac0 "The request timed out."}

I thought that by virtue of specifying that the cache should be used when there's a timeout, with: "RKRequestCachePolicyTimeout", I would have expected the user to be retrieved from the local cache.

The cache does contain a user record with ID 123 -- in the ZUSER table, with 123 in the ZIDENTIFIER column.

Is there a step that I am missing to get this to work? Maybe another delegate method that needs to be handled, or is called, when the cache is hit after the timeout? Or am I trying to do something which is not necessarily something you'd get "out of the box" with RestKit?

Cheers.

Answers


You might use the Reachability Class to determine wether your client is offline or not. I use this great class very often in every project that requires an internet connection.

You simply start the notifier to a specific host. In all of your viewController you now just have to register methods to the NSNotificationCenter to set a BOOL isOnline for example.

Doing this practice you can do beautiful stuff in your app like overlaying the app with a smooth "Offline" message.

https://gist.github.com/1182373

EDIT

Heres one example from the login screen from one of my projects (sorry for this quantity of code but this is my complete implementation):

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    //// Some stuff ////
    [[Reachability reachabilityWithHostname:@"apple.com"] startNotifier];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:) name:kReachabilityChangedNotification object:nil];
}
- (void)reachabilityChanged:(NSNotification *)note
{
    if ([[note object] isReachable]) {
        CAKeyframeAnimation *scale = [CAKeyframeAnimation animationWithKeyPath:@"transform.scale"];
        [scale setValues:[NSArray arrayWithObjects:[NSNumber numberWithFloat:1.0], [NSNumber numberWithFloat:0.0], nil]];
        [scale setDuration:0.3];
        [scale setRemovedOnCompletion:NO];

        [[offlineView layer] setTransform:CATransform3DMakeScale(0, 0, 1.0)];
        [[offlineView layer] addAnimation:scale forKey:@"scale"];
        [[offlineView layer] setTransform:CATransform3DIdentity];

        [UIView animateWithDuration:0.3 animations:^{
            [offlineView setAlpha:0];
        } completion:^(BOOL finished){
            if (finished) {
                [offlineView removeFromSuperview];
            }
        }];

        [[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleDefault animated:YES];
    }
    else {
        CGRect screenFrame = CGRectMake(0, 0, 320, 480);

        offlineView = [[UIView alloc] initWithFrame:screenFrame];
        [offlineView setBackgroundColor:[UIColor colorWithWhite:0 alpha:0.7]];
        [offlineView setAlpha:0];

        offlineLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 200, 30)];
        [offlineLabel setFont:[UIFont fontWithName:@"Verdana" size:30.0]];
        [offlineLabel setBackgroundColor:[UIColor clearColor]];
        [offlineLabel setTextAlignment:UITextAlignmentCenter];
        [offlineLabel setTextColor:[UIColor whiteColor]];
        [offlineLabel setCenter:[offlineView center]];
        [offlineLabel setText:@"OFFLINE"];

        [offlineView addSubview:offlineLabel];
        [[self window] addSubview:offlineView];

        [UIView animateWithDuration:0.3 animations:^{
            [offlineView setAlpha:1.0];
        }];

        [[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleBlackTranslucent animated:YES];
    }
}

Please check the version of RestKit; in the newer version of RestKit there is slightly changed approach of getting the cached data from managed object store. I don't have the example at this machine; but If you need help any more (since this a rather old question) please reply.


Need Your Help

Jquery validate custom file input

jquery file validation input hidden

I'm trying to validate a custom styled file input that is part of a multi page html-form. The input itself is hidden and controlled via its label.

Have an editable matrix in MVC

asp.net .net asp.net-mvc razor

Im using MVC and Razor to develop an application for administrative purposes. Using the model shown below, im trying to display a matrix that the user can edit. For each row, there is a start and a...