[ACCEPTED]-iOS: Why can't I set nil to NSDictionary value?-null
You can set a nil value using setValue:forKey but it removes the key.
If you want to be able to set a key to nil you 12 could use setValue:forKey: which will remove the key if 11 you set it to nil (quote from documentation 10 below). Note the Value instead of Object.
setValue:forKey:Adds 9 a given key-value pair to the dictionary.
Discussion...This 8 method adds value and key to the dictionary 7 using
setObject:forKey:, unless value isnilin which case the 6 method instead attempts to remove key using 5removeObjectForKey:.
When you later try and get the object using 4 objectForKey: for the key that you removed by setting 3 it to nil you will get nil back (quote from documentation 2 below).
Return value:The value associated with aKey, or 1 nil if no value is associated with aKey.
Note: The key will not actually be present in the dictionary so it won't be obtained using allKeys; or be enumerated over.
You can set nil object in this way:
NSMutableDictionary *dictionary = [NSMutableDictionary dictionary];
dictionary[@“key”] = nil;
Have 1 you noticed it?
NSMutableDictionary *dictionary = [NSMutableDictionary dictionary];
/* this statement is safe to execute */
dictionary[@“key”] = nil;
/* but this statement will crash application */
[dictionary setObject:nil forKey:@"key"];
When using this method:
func setObject(_ anObject: Any, forKey aKey: NSCopying)
Parameters (according to Apple doc's):
anObject:
Raises 5 an invalidArgumentException if anObject 4 is nil. If you need to represent a nil 3 value in the dictionary, use NSNull .
aKey
Raises 2 an invalidArgumentException if aKey is 1 nil.
My friend using nil as marker is a sign 6 of bad programming . nil is reserved for 5 some diffrent purpose .
if([q objectForKey:@"text"] != nil)
[dict setObject:[q objectForKey:@"text"] forKey:@"text"];
else
[dict removeObjectforKey:@"text"]; // this will do nothing if key does not exsist.
//by default for 4 all the keys the value is nil and you are 3 trying to override this behavior. going 2 against the language rules will always get 1 you in trouble .
to check just use
if([dict objectforKey:@"text"] !=nil){} // this will work becuase default value is nil
itself
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