ios - 如何在Objective-C中捕获JSON错误？

Question

遵循本教程:http://www.raywenderlich.com/5492/working-with-json-in-ios-5，我制作了一个简单的应用程序，如下所示:

#define kLatestKivaLoansURL [NSURL URLWithString: @"http://api.kivaws.org/v1/loans/search.json?status=fundraising"] 

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        NSData* data = [NSData dataWithContentsOfURL: kLatestKivaLoansURL];
        NSError* error;
        NSDictionary* json = [NSJSONSerialization JSONObjectWithData:data 
                                                             options:kNilOptions
                                                               error:&error];
        NSArray* latestLoans = [json objectForKey:@"loans"];
        NSLog(@"Error: %@",error);
        NSLog(@"loans: %@",latestLoans); 

        dispatch_async(dispatch_get_main_queue(), ^(){
            self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
            self.viewController = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
            self.window.rootViewController = self.viewController;
            [self.window makeKeyAndVisible];
        });

    });

    return YES;
}

@end

当网络不正常或JSON链接错误时，我得到相同的中断:“*由于未捕获的异常'NSInvalidArgumentException'而终止应用程序，原因:'数据参数为nil'”

如何捕获此错误？我只想显示一个警报消息，而不是中断。

解析JSON数据时会发生几种错误？

Answer 1

您应该检查NSData* data是否为nil？如果为零，则不应运行代码行

NSDictionary* json = [NSJSONSerialization JSONObjectWithData:data 
                                                             options:kNilOptions
                                                               error:&error];

当您尝试将 nil数据转换为 Dictionary时。

您还可以通过在代码中实现可达性类来检查网络可用性。一个示例应用程序演示了如何使用SystemConfiguration框架来监视iPhone或iPod touch的网络状态。

http://developer.apple.com/library/ios/#samplecode/Reachability/Introduction/Intro.html