目标c – 获得空值

我一直坚持这一段时间了，但最新发生的是，当从MySQL请求回来有一个空值，但我如何检查空值已经打我的条件，所以我不存储这个值在数组。 代码如下

我一直得到的错误是 – [NSNull isEqualToString：]：无法识别，即时尝试绑定在一个tableview中的数组

- (void)viewDidLoad { JobAddSiteAppDelegate *ja = (JobAddSiteAppDelegate *)[[UIApplication sharedApplication] delegate]; tempArray = [[NSMutableArray alloc] init]; NSString *strURL = [NSString stringWithFormat:@"http://www.bestitjobs.co.uk/appresults3.php", ""]; NSData *nsData = [NSData dataWithContentsOfURL:[NSURL URLWithString: strURL]]; //NSLog(@"JSON: %@", nsData); //NSString *strResult = [[[NSString alloc] initWithData:nsData encoding:NSUTF8StringEncoding] autorelease]; //NSLog(@"Result: %@",strResult); //NSError *e = nil; JSONDecoder* decoder = [[JSONDecoder alloc] init]; NSDictionary* listDictionary = [nsData objectFromJSONData]; NSArray* people =[listDictionary objectForKey:@"jobs"]; for (NSDictionary *person in people) { NSLog(@"people %@",people); if([person objectForKey:@"position"] != [NSNull class]) { NSString *position = [person objectForKey:@"position"]; NSLog(@"position %@",position); [tempArray addObject: position]; } } self.listData = tempArray; [tempArray release]; [listData release]; [super viewDidLoad]; } 

错误

2012-12-06 12：22：11.314 JobAddSite [7718：207]职位高级networking和系统顾问2012-12-06 12：22：11.316 JobAddSite [7718：207] position SAP Business One / SAP B1顾问伦敦2012-12-12 -06 12：22：11.317 JobAddSite [7718：207]职位业务开发经理 – 市场领先的IT公司2012-12-06 12：22：11.318 JobAddSite [7718：207] – [NSNull isEqualToString：]：无法识别的select器发送到实例0xe565e8 2012-12-06 12：22：11.321 JobAddSite [7718：207] *由于未捕获的exception'NSInvalidArgumentException'，原因：' – [NSNull isEqualToString：]：无法识别的select器发送到实例0xe565e8'* *抛出：（0 CoreFoundation 0x00de95a9 exceptionPreprocess + 185 1 libobjc.A.dylib 0x00f3d313 objc_exception_throw + 44 2 CoreFoundation 0x00deb0bb – [NSObject（NSObject）doesNotRecognizeSelector：] + 187 3 CoreFoundation 0x00d5a966 __ forwarding + 966 4 CoreFoundation 0x00d5a522 _CF_forwarding_prep_0 + 50 5 JobAddSite 0x000024cd – [ResultViewController v iewDidLoad] + 604 6 UIKit 0x00389089 – [UIViewController view] + 179 7 UIKit 0x0038aa3d – [UIViewController viewControllerForRotation] + 63 8 UIKit 0x00386988 – [UIViewController _visibleView] + 90 9 UIKit 0x0062893c – [UIClientRotationContext initWithClient：toOrientation：duration：andWindow：] + 354 10 UIKit 0x0030081e – [UIWindow _setRotatableClient：toOrientation：updateStatusBar：duration：force：] + 954 11 UIKit 0x00588619 – [UIWindowController transition：fromViewController：toViewController：target：didEndSelector：] + 1381 12 UIKit 0x0038d65d – [UIViewController presentModalViewController：withTransition：] + 3478 13 JobAddSite 0x0000213f – [JobAddSiteViewController search] + 270 14 UIKit 0x002d94fd – [UIApplication sendAction：to：from：forEvent：] + 119 15 UIKit 0x00369799 – [UIControl sendAction：to：forEvent：] + 67 16 UIKit 0x0036bc2b – [UIControl （Internal）_sendActionsForEvents：withEvent：] + 527 17 UIKit 0x0036a7d8 – [UIControl touchesEnded：withEvent：] + 458 18 UIKit 0x002fdded – [UIWindow _sendTouchesFor 事件：] + 567 19的UIKit 0x002dec37 – [UIApplication的的SendEvent：] + 447 20的UIKit 0x002e3f2e _UIApplicationHandleEvent + 7576 21个GraphicsServices 0x01741992 PurpleEventCallback + 1550 22的CoreFoundation 0x00dca944 CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION + 52 23的CoreFoundation 0x00d2acf7 __CFRunLoopDoSource1 + 215 24的CoreFoundation 0x00d27f83 __CFRunLoopRun + 979 25的CoreFoundation 0x00d27840 CFRunLoopRunSpecific + 208 26 CoreFoundation 0x00d27761 CFRunLoopRunInMode + 97 27 GraphicsServices 0x017401c4 GSEventRunModal + 217 28 GraphicsServices 0x01740289 GSEventRun + 115 29 UIKit 0x002e7c93 UIApplicationMain + 1160 30 JobAddSite 0x00001dec main + 102 31 JobAddSite 0x00001d7d start + 53）抛出“NSException”

Answer 1

试试这个：

 if ([person objectForKey:@"position"]) {..} 

这一个是相同的，但也许更可读：

 if ([person objectForKey:@"position"] != nil) {..} 

Answer 2

嗨使用下面的代码。

它工作得很好。

下载支持文件

 NSMutableArray *empArray = [[NSMutableArray alloc] init]; SBJSON *parser = [[SBJSON alloc] init]; NSURLRequest *request1 = [NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://www.bestitjobs.co.uk/appresults3.php"]]]; NSLog(@"GGGG:%@",request1); NSData *response1 = [NSURLConnection sendSynchronousRequest:request1 returningResponse:nil error:nil]; NSString *json_string = [[NSString alloc] initWithData:response1 encoding:NSUTF8StringEncoding]; NSDictionary *statuses = [parser objectWithString:json_string error:nil]; NSLog(@"List Dictionary:%@",statuses); NSArray* people =[statuses objectForKey:@"jobs"]; for(NSDictionary *test in people) { [empArray addObject:[test valueForKey:@"position"]]; } NSLog(@"EMP ARRAY CATEGORY:%@",empArray); 

注意：在使用SBJSon支持文件并导入JSON.h之前

并检查您的控制台。

Answer 3

像这样检查条件，并为Array添加值

 for (NSDictionary *person in people) { NSLog(@"people %@",people); NSString *position = [person objectForKey:@"position"]; if(position) { [tempArray addObject: position]; } }