目标 c - 获取空值

Question

我已经坚持了一段时间了，但是发生的事情是，当请求从 mysql 返回时，有一个空值，但是我如何检查空值是否达到了我的条件，以便我不存储这个值在数组中。代码如下

我不断收到的错误是 -[NSNull isEqualToString:]: unrecognized and im trying to bind the array inside a tableview

- (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] 职位高级网络和系统顾问 2012-12-06 12:22:11.316 JobAddSite[7718:207] 职位 SAP Business One / SAP B1 顾问伦敦 2012-12-06 12:22:11.317 JobAddSite[7718:207] 职位业务发展经理 - 市场领先的 IT 公司 2012-12-06 12:22:11.318 JobAddSite[7718:207]-[NSNull isEqualToString:]：无法识别的选择器发送到实例 0xe565e8 2012-12-06 12:22:11.321 JobAddSite[7718:207] * 由于未捕获的异常“NSInvalidArgumentException”而终止应用程序，原因：“-[NSNull isEqualToString:]：无法识别的选择器发送到实例 0xe565e8” * 在第一次抛出时调用堆栈： ( 0 CoreFoundation 0x00de95a9 异常预处理 + 185 1 libobjc.A.dylib 0x00f3d313 objc_exception_throw + 44 2 核心基础 0x00deb0bb -[NSObject(NSObject) 不识别选择器：] + 187 3 CoreFoundation 0x00d5a966 __转发 + 966 4 核心基础 0x00d5a522 _CF_forwarding_prep_0 + 50 5 JobAddSite 0x000024cd -[ResultViewController viewDidLoad] + 604 6 UIKit 0x00389089 -[UIViewController 视图] + 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 转换：fromViewController:toViewController:target:didEndSelector:] + 1381 12 UIKit 0x0038d65d-[UIViewController presentModalViewController:withTransition:] + 3478 13 JobAddSite 0x0000213f -[JobAddSiteViewController 搜索] + 270 14 UIKit 0x002d94fd-[UIApplication sendAction:to:from:forEvent:] + 119 15 UIKit 0x00369799-[UIControl sendAction:to:forEvent:] + 67 16 UIKit 0x0036bc2b-[UIControl（内部）_sendActionsForEvents:withEvent:] + 527 17 UIKit 0x0036a7d8-[UIControl touchesEnded:withEvent:] + 458 18 UIKit 0x002fdded-[UIWindow_sendTouchesForEvent:] + 567 19 UIKit 0x002dec37-[UIApplication 发送事件：] + 447 20 UIKit 0x002e3f2e _UIApplicationHandleEvent + 7576 21 图形服务 0x01741992 PurpleEventCallback + 1550 22 核心基础 0x00dca944 CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION + 52 23 核心基础 0x00d2acf7 __CFRunLoopDoSource1 + 215 24 核心基础 0x00d27f83 __CFRunLoopRun + 979 25 核心基础 0x00d27840 CFRunLoopRunSpecific + 208 26 核心基础 0x00d27761 CFRunLoopRunInMode + 97 27 图形服务 0x017401c4 GSEventRunModal + 217 28 图形服务 0x01740289 GSEventRun + 115 29 UIKit 0x002e7c93 UIApplicationMain + 1160 30 JobAddSite 0x00001dec 主要 + 102 31 JobAddSite 0x00001d7d 开始 + 53 ) 在抛出 'NSException' 的实例后调用终止

Answer 1

试试这个：

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

这个是一样的，但可能更具可读性：

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

Answer 2

您好，请使用以下代码。

运行良好。

Download Supporting Files

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

然后检查您的控制台。

Answer 3

像这样检查条件并为数组添加值

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