我返回了一个JSON负载，该负载可能为null或value。类似：
post: {
header:"here is my header",
current_instore_anncouncement: null
}
或者当存在current_instore_announcement:时
post: {
header:"here is my header",
current_instore_anncouncement: {header: "announcement header"}
}
我使用的是AFNetworking 2.0，如果current_isntore_announcement存在，我想显示它，如果它返回null，我想什么都不做。
如何正确检查current_instore_anncouncement的存在？我有：
NSDictionary *current_instore_announcement=[result objectForKey:@"current_instore_anncouncement"];
if(current_instore_announcement){
InstoreAnnoucement *splashAnnouncement = [[InstoreAnnoucement alloc] initWithAttributes:current_instore_announcement];
if(splashAnnouncement){
NSLog(@"theres an instore announcement");
}else{
NSLog(@"nadda = instore announcement with %@",current_instore_announcement);
}
}
但我得到以下错误：
[NSNull notNullObjectForKey:]: unrecognized selector sent to instance
编辑#1
看起来最好的方法是检查它是否为NSNull。像这样：
if(![current_instore_announcement isEqual:[NSNull class]]){
或者创建一个NSDictionary的添加，如下所示：
#import "NSDictionary+Additions.h"
@implementation NSDictionary (Additions)
- (id)notNullObjectForKey:(id)aKey {
id obj = [self objectForKey:aKey];
if ([obj isKindOfClass:[NSNull class]]) {
return nil;
}
return obj;
}
还有其他更好的想法吗？
i使用以下方法：
if(![current_instore_announcement isEqual:[NSNull class]]){
// Not null
}
else{
// null
}
检查这一点的好方法是使用以下方法。请检查这个：
- (BOOL) hasValue:(id)object {
if(object!=nil && (NSNull *)object != [NSNull null]) {
// Check NSString Class
if([object isKindOfClass:[NSString class]] || [object isKindOfClass:[NSMutableString class]]) {
if([object length]>0) {
return YES;
}
}
// Check UIImage Class
if([object isKindOfClass:[UIImage class]]){
if ([object CGImage]!=nil) {
return YES;
}
}
// Check NSArray Class
if ([object isKindOfClass:[NSArray class]] || [object isKindOfClass:[NSMutableArray class]]) {
if ([object count] > 0) {
return YES;
}
}
else {
return YES;
}
}
return NO;
}
并且您必须每次检查json响应中的每个对象。
您可以使用[myDisctionary allKeys];进行检查
例如：
NSDictionary *current_instore_announcement=[result objectForKey:@"current_instore_anncouncement"];
// get the keys
NSArray *keys = [current_instore_announcement allKeys];
if([keys count]>0){
// do something with the dictionary.
}else
// Null Values
NSDictionary *current_instore_announcement=[result objectForKey:@"current_instore_anncouncement"];
if ([current_instore_announcement isKindOfClass:[NSDictionary class]]){
//nil or null will not be here, and just do NSDictionary parsing here
}
否则：
if (![current_instore_announcement isKindOfClass:[NSNull class]]){
//not null class will be here, NSDictionary, nil, empty string will all be parsed here
}