When you’re just getting started with Objective C,
it’s easy to fall into the trap of doing things the easy way, especially when
working with JSON. But if you parse JSON the easy way, your app will
crash, and you’ll be scratching your head wondering why. For your users and for
your own sanity, don’t build apps that crash – be sure that when you parse
JSON, you do it the safe way, not the easy way.
Let’s start with some simple JSON we’d like to
parse:
{
"data": [ {"name":"chandan"},
{"name":"vipul"}
]
}
You will
parse this JSON like
NSArray* array = [dict objectForKey@"data"];
And you will receive a array of dictionary in "array". But now
imagine a situation when a key "data" is now not containing an array
or a key has been changed. Now what will happen, your APP will get crashed
because it has not found an array. So to avoid these kind of crashes just
create a category of your dictionary and add some methods as shown below.
#import "NSDictionary+RMDictionary.h"
@implementation NSDictionary (RMDictionary)
- (BOOL) boolForKey:(NSString*)aKey
{
NSObject* value = [self valueForKey:aKey];
if ([value isKindOfClass:[NSNumber class]])
{
NSNumber* num = (NSNumber*)value;
return num.boolValue;
}
else
return NO;
}
- (NSInteger) integerForKey:(NSString*)key
{
NSObject* value = [self valueForKey:key];
if ([value isKindOfClass:[NSNumber class]])
{
return ((NSNumber*)value).integerValue;
}
return 0;
}
- (NSString*) stringForKey:(NSString*)key
{
id value = [self valueForKey:key];
if ([value isKindOfClass:[NSString class]])
{
return (NSString*)value;
}
return @"";
}
- (NSDate*) dateForKey:(NSString*)key
{
NSString* value = [self stringForKey:key];
NSDateFormatter* formatter = [[NSDateFormatter alloc]init];
[formatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss"];
NSDate* date = [formatter dateFromString:value];
if (date)
{
return date;
}
return [NSDate dateWithTimeIntervalSince1970:0];
}
-(NSArray*) arrayForKey:(NSString*)key
{
id value = [self valueForKey:key];
if([value isKindOfClass:[NSArray class]])
{
return (NSArray*)value;
}
return [[NSArray alloc] init];
}
- (NSNumber*) numberForKey:(NSString*)key
{
NSObject* value = [self valueForKey:key];
if ([value isKindOfClass:[NSNumber class]])
{
return (NSNumber*)value;
}
return 0;
}
- (NSDictionary*) dictionaryForKey:(NSString*)key
{
id value = [self valueForKey:key];
if([value isKindOfClass:[NSDictionary class]])
{
return (NSDictionary*)value;
}
return [[NSDictionary alloc] init];
}
@end
Now instead of using "objectForKey" start using
"arrayForKey" or "stringForKey". This will now avoid your
APP crash, because if array is not found it will create an empty array and then
return.
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