RestKit iOS应用程序的在线和离线支持

Question

我想将RestKit用于一个需要在联机和脱机时都能工作的应用程序。

我可能误解了RestKit的工作原理，但我认为这（相当）容易实现。

在一个iOS应用程序的划痕测试中，我设置如下：

// setup the client
NSString* URL = @"http://10.211.55.5:3000/api";
RKClient* client = [RKClient clientWithBaseURL:URL];
client.username = @"[e-mail]";
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"];

User对象是根据CoreData支持的要求实现的：

@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

这是MyCache。请注意，我不想检查resourcePath，因为这只是为了尝试一下，而且我有一条路径。

@implementation MyCache
- (NSArray*)fetchRequestsForResourcePath:(NSString*)resourcePath
{
    NSFetchRequest* fetchRequest = [User fetchRequest];
    return [NSArray arrayWithObject:fetchRequest];
}
-(BOOL)shouldDeleteOrphanedObject:(NSManagedObject *)managedObject
{
    return true;
}
@end

然后我打电话给服务器，以获取id为123的用户，路径为"/api/users/123"：

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

这很好用。但是，当我断开Mac上的wifi时，上面的代码不会从sqlite数据库中检索用户。

我在代理的objectLoader:didFailWithError:中得到以下错误

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."}

我认为，通过指定在超时时应使用缓存，并使用："RKRequestCachePolicyTimeout"，我会期望从本地缓存中检索用户。

缓存确实包含一个ID为123的用户记录——在ZUSER表中，其中123在ZIDENTIFIER列中。

我是否错过了一个让它发挥作用的步骤？也许是另一种委托方法在超时？还是我在尝试做一些你不一定会用RestKit"开箱即用"的事情？

干杯。

Answer 1

您可以使用可达性类来确定您的客户端是否离线。我经常在每个需要互联网连接的项目中使用这个很棒的课程。

您只需启动特定主机的通知程序。在所有的viewController中，您现在只需向NSNotificationCenter注册方法，即可设置BOOL isOnline。

通过这种练习，你可以在应用程序中做一些漂亮的事情，比如用平滑的"离线"消息覆盖应用程序。

https://gist.github.com/1182373

编辑

以下是我的一个项目的登录屏幕上的一个例子（很抱歉有这么多代码，但这是我的完整实现）：

- (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];
    }
}

Answer 2

请检查RestKit的版本；在RestKit的新版本中，从托管对象存储中获取缓存数据的方法略有改变。我没有这台机器的例子；但如果你还需要帮助（因为这是一个相当古老的问题），请回答。