我有一段代码，可以检测NSString是否为NULL、nil等.但是，它崩溃了.这是我的代码:
NSArray *resultstwo = [database executeQuery:@"SELECT * FROM processes WHERE ready='yes' LIMIT 0,1"];
for (NSDictionary *rowtwo in resultstwo) {
NSString *getCaption = [rowtwo valueForKey:@"caption"];
if (getCaption == NULL) {
theCaption = @"Photo uploaded...";
} else if (getCaption == nil) {
theCaption = @"Photo uploaded...";
} else if ([getCaption isEqualToString:@""]) {
theCaption = @"Photo uploaded...";
} else if ([getCaption isEqualToString:@" "]) {
theCaption = @"Photo uploaded...";
}
}
下面是错误:
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 Select 器已发送到实例0x3eba63d4"
我做错什么了吗？我需要换一种方式吗？