ios - Objective-C 中的 SIGBRT 错误，可能来自尝试的 JSON 请求

Question

我在 Objective-C 中处理简单的 JSON 请求时遇到了问题。当我尝试执行代码时，它给了我这个错误:

2015-08-11 12:11:15.552 WordADay[11482:1877243] *** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<__NSCFString 0x7fa4d8e87270> valueForUndefinedKey:]: this class is not key value coding-compliant for the key text.'
*** First throw call stack:
(
    0   CoreFoundation                      0x000000010c01bc65 __exceptionPreprocess + 165
    1   libobjc.A.dylib                     0x000000010bcb4bb7 objc_exception_throw + 45
    2   CoreFoundation                      0x000000010c01b8a9 -[NSException raise] + 9
    3   Foundation                          0x000000010b8da82a -[NSObject(NSKeyValueCoding) valueForUndefinedKey:] + 226
    4   Foundation                          0x000000010b833b23 -[NSObject(NSKeyValueCoding) valueForKey:] + 251
    5   WordADay                            0x000000010b7823f2 -[ViewController getNewWord] + 1442
    6   WordADay                            0x000000010b781e09 -[ViewController viewDidLoad] + 73
    7   UIKit                               0x000000010c5451d0 -[UIViewController loadViewIfRequired] + 738
    8   UIKit                               0x000000010c5453ce -[UIViewController view] + 27
    9   UIKit                               0x000000010c460289 -[UIWindow addRootViewControllerViewIfPossible] + 58
    10  UIKit                               0x000000010c46064f -[UIWindow _setHidden:forced:] + 247
    11  UIKit                               0x000000010c46cde1 -[UIWindow makeKeyAndVisible] + 42
    12  UIKit                               0x000000010c410417 -[UIApplication _callInitializationDelegatesForMainScene:transitionContext:] + 2732
    13  UIKit                               0x000000010c41319e -[UIApplication _runWithMainScene:transitionContext:completion:] + 1349
    14  UIKit                               0x000000010c412095 -[UIApplication workspaceDidEndTransaction:] + 179
    15  FrontBoardServices                  0x000000010ebd55e5 __31-[FBSSerialQueue performAsync:]_block_invoke_2 + 21
    16  CoreFoundation                      0x000000010bf4f41c __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 12
    17  CoreFoundation                      0x000000010bf45165 __CFRunLoopDoBlocks + 341
    18  CoreFoundation                      0x000000010bf44f25 __CFRunLoopRun + 2389
    19  CoreFoundation                      0x000000010bf44366 CFRunLoopRunSpecific + 470
    20  UIKit                               0x000000010c411b02 -[UIApplication _run] + 413
    21  UIKit                               0x000000010c4148c0 UIApplicationMain + 1282
    22  WordADay                            0x000000010b782aaf main + 111
    23  libdyld.dylib                       0x000000010e5bf145 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb) 

当我不尝试执行这个奇怪的 JSON 请求时，它执行得很好......但是当我这样做时，它会抛出该错误。我想知道我应该做什么...这是 JSON 请求背后的代码:

//
//  ViewController.m
//  WordADay
//
//  Created by Lucas Steuber on 8/11/15.
//  Copyright (c) 2015 Lucas Steuber. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UILabel *word;
@property (weak, nonatomic) IBOutlet UILabel *definition;

@end

@implementation ViewController
- (IBAction)newWord:(id)sender {
    [self getNewWord];
}

- (IBAction)moreInfo:(id)sender {

}

- (void)viewDidLoad {
    [super viewDidLoad];
    [self getNewWord];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (void)getNewWord {
    NSBundle *mainBundle = [NSBundle mainBundle];
    NSString *filePath = [mainBundle pathForResource:@"dictionary" ofType:@"txt"];
    NSString *fileContents = [NSString stringWithContentsOfFile:filePath encoding:NSUTF8StringEncoding error:nil];

    NSArray *values = [fileContents componentsSeparatedByCharactersInSet:[NSCharacterSet newlineCharacterSet]];


    NSUInteger randomIndex = arc4random() % [values count];
    NSString *word = values[randomIndex];

    NSString *urlp1 = @"http://api.wordnik.com:80/v4/word.json/";
    NSString *urlp2 = @"/definitions?limit=1&includeRelated=true&sourceDictionaries=wiktionary&useCanonical=false&includeTags=false&api_key=a2a73e7b926c924fad7001ca3111acd55af2ffabf50eb4ae5";
    NSURL *wordnik = [NSURL URLWithString: [NSString stringWithFormat: @"%@%@%@", urlp1, word, urlp2]];

    NSURLRequest *urlRequest = [NSURLRequest requestWithURL:wordnik
                                                cachePolicy:NSURLRequestReturnCacheDataElseLoad
                                            timeoutInterval:30];
    // Fetch the JSON response
    NSData *urlData;
    NSURLResponse *response;
    NSError *error;
    NSError *jsonArrayError;
    NSString *desc;

    // Make synchronous request
    urlData = [NSURLConnection sendSynchronousRequest:urlRequest
                                    returningResponse:&response
                                                error:&error];

    NSArray *jsonArray = [NSJSONSerialization JSONObjectWithData: urlData options: NSJSONReadingMutableContainers error: &jsonArrayError];

    if (!jsonArray) {
        NSLog(@"Error parsing JSON: %@", jsonArrayError);
    } else {
        NSArray *items = [jsonArray objectAtIndex:0];
        for (NSDictionary *item in items){
            desc = [item valueForKey:@"text"];
        }
    }


    self.word.text = word;
    self.definition.text = desc;
}
@end

我对 Objective-C 还很陌生，到目前为止我还不太喜欢它。

编辑:这是我正在解析的 JSON:

[{"textProns":[],"sourceDictionary":"wiktionary","exampleUses":[],"relatedWords":[],"labels":[],"citations":[],"word":"hello","partOfSpeech":"interjection","attributionText":"from Wiktionary, Creative Commons Attribution/Share-Alike License","attributionUrl":"http://creativecommons.org/licenses/by-sa/3.0/","text":"A greeting (salutation) said when meeting someone or acknowledging someone’s arrival or presence.","score":0.0}]

Answer 1

您的 JSON 是一个包含一个字典的数组。但是您的代码采用了不同的结构。以下应符合实际数据格式:

NSArray *jsonArray = [NSJSONSerialization JSONObjectWithData: urlData options: NSJSONReadingMutableContainers error: &jsonArrayError];

if (!jsonArray) {
    NSLog(@"Error parsing JSON: %@", jsonArrayError);
} else {
    for (NSDictionary *item in jsonArray){
        desc = item[@"text"];
    }
}

但是遍历一个字典是没有意义的，所以它可以简化为:

NSArray *jsonArray = [NSJSONSerialization JSONObjectWithData: urlData options: NSJSONReadingMutableContainers error: &jsonArrayError];

if (!jsonArray) {
    NSLog(@"Error parsing JSON: %@", jsonArrayError);
} else {
    NSDictionary *item = [jsonArray firstObject];
    desc = item[@"text"];
}

另请注意，您不应使用 valueForKey: 从 NSDictionary 中获取值。使用 objectForKey: 或现代语法(就像我在此处的代码中所做的那样)。