使用 NSJSONSerialization 解析 JSON - 抛出 NSException

Question

我正在使用NSJSONSerialization 来解析从 PHP 页面下拉的 JSON。以下代码用于解析 JSON 并显示数据字段的值（首先包含 JSON 示例）：

{"status":200,"status_message":"Book Found","data":348}

代码：

- (IBAction)btnClick:(id)sender
{
    if(![_txtBox.text isEqual:@""])
    {
        NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"http://www.mysite.comm/project/ws/name/%@",@"c"]]; //url for JSON

        NSError *jsonError=nil;

        NSString *jsonString = [self jsonStringWithUrl:url]; //get data as JSON

        NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding]; //convert to data

        NSDictionary *jsonObject = [NSJSONSerialization JSONObjectWithData:jsonData options:kNilOptions error: &jsonError];

        _txtView.text = (NSString *)[jsonObject objectForKey:@"data"];
    }
}

但是，代码崩溃并且我收到以下错误消息。我怀疑它与这条线有关：_txtView.text = (NSString *)[jsonObject objectForKey:@"data"]; 但我不确定要寻找什么。我是否试图以错误的方式从NSDictionary 获取数据？

2014-03-23 22:04:35.292 WebServiceTest[38975:60b] -[__NSCFNumber length]: unrecognized selector sent to instance 0x8d7f140
2014-03-23 22:04:35.296 WebServiceTest[38975:60b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFNumber length]: unrecognized selector sent to instance 0x8d7f140'
*** First throw call stack:
(
    0   CoreFoundation                      0x017ec1e4 __exceptionPreprocess + 180
    1   libobjc.A.dylib                     0x0156b8e5 objc_exception_throw + 44
    2   CoreFoundation                      0x01889243 -[NSObject(NSObject) doesNotRecognizeSelector:] + 275
    3   CoreFoundation                      0x017dc50b ___forwarding___ + 1019
    4   CoreFoundation                      0x017dc0ee _CF_forwarding_prep_0 + 14
    5   Foundation                          0x011894e4 -[NSConcreteAttributedString length] + 42
    6   Foundation                          0x01188a6c -[NSConcreteAttributedString initWithString:attributes:] + 182
    7   UIKit                               0x00939e9d -[UITextView setText:] + 125
    8   WebServiceTest                      0x00002922 -[WebServiceTestViewController btnClick:] + 610
    9   libobjc.A.dylib                     0x0157d880 -[NSObject performSelector:withObject:withObject:] + 77
    10  UIKit                               0x0022d3b9 -[UIApplication sendAction:to:from:forEvent:] + 108
    11  UIKit                               0x0022d345 -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 61
    12  UIKit                               0x0032ebd1 -[UIControl sendAction:to:forEvent:] + 66
    13  UIKit                               0x0032efc6 -[UIControl _sendActionsForEvents:withEvent:] + 577
    14  UIKit                               0x0032e243 -[UIControl touchesEnded:withEvent:] + 641
    15  UIKit                               0x0026cddd -[UIWindow _sendTouchesForEvent:] + 852
    16  UIKit                               0x0026d9d1 -[UIWindow sendEvent:] + 1117
    17  UIKit                               0x0023f5f2 -[UIApplication sendEvent:] + 242
    18  UIKit                               0x00229353 _UIApplicationHandleEventQueue + 11455
    19  CoreFoundation                      0x0177577f __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
    20  CoreFoundation                      0x0177510b __CFRunLoopDoSources0 + 235
    21  CoreFoundation                      0x017921ae __CFRunLoopRun + 910
    22  CoreFoundation                      0x017919d3 CFRunLoopRunSpecific + 467
    23  CoreFoundation                      0x017917eb CFRunLoopRunInMode + 123
    24  GraphicsServices                    0x037e05ee GSEventRunModal + 192
    25  GraphicsServices                    0x037e042b GSEventRun + 104
    26  UIKit                               0x0022bf9b UIApplicationMain + 1225
    27  WebServiceTest                      0x000022fd main + 141
    28  libdyld.dylib                       0x01e33701 start + 1
    29  ???                                 0x00000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb) 

Answer 1

您显示的 JSON 对象将 348 列为整数值。因此，当NSJSONSerialization 得到它时，它会将其转换为 NSNumber。您需要在[jsonObject objectForKey:@"data"] 上调用-[NSNumber stringValue] 以将NSNumber 转换为NSString。