objective-c - 对 RestKit iOS 应用程序的在线和离线支持

Question

我想将 RestKit 用于需要在线和离线工作的应用程序。

我可能误解了 RestKit 的工作原理，但我认为这(相当)容易实现。

在 iOS 应用程序的 scratch 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 = @"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"];

用户对象是根据 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

这是我的缓存。请注意，我没有费心去检查 resourcePath，因为这只是为了尝试，而且我有一条路。

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

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

然后我调用服务器以获取 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。

我在委托(delegate)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，使用:“RKRequestCachePolicyTimeout”，我希望从本地缓存中检索用户。

缓存确实包含 ID 为 123 的用户记录 -- 在 ZUSER 表中，ZIDENTIFIER 列中有 123。

我是否缺少使它正常工作的步骤？也许是另一个委托(delegate)方法需要在缓存命中后被处理或调用暂停？还是我正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 Reachability Class 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类(class)。

您只需启动特定主机的通知程序。在您所有的 viewController 中，您现在只需将方法注册到 NSNotificationCenter 以设置 BOOL isOnline，例如。

通过这种练习，您可以在您的应用中做一些漂亮的事情，比如用流畅的“离线”消息覆盖应用。

https://gist.github.com/1182373

编辑

这是我的一个项目的登录屏幕中的一个示例(抱歉代码量如此之大，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];
    }
}