How do you check for null in Objective-C?

So to check against NSNull one can either use: if ((NSNull *)getCaption == [NSNull null]) ……In Objective-C:

  1. nil (all lower-case) is a null pointer to an Objective-C object.
  2. Nil (capitalized) is a null pointer to an Objective-C class.
  3. NULL (all caps) is a null pointer to anything else (C pointers, that is).

What sending a message to nil means and how is it actually useful?

In Objective-C, it is valid to send a message to nil —it simply has no effect at runtime. There are several patterns in Cocoa that take advantage of this fact. The value returned from a message to nil may also be valid: If the method returns an object, then a message sent to nil returns 0 ( nil ).

How do you check if a string is empty or null in Objective-C?

= nil if myOptionalNSString == nil || myOptionalNSString!. length == 0 { print(“String is empty.”) } // or alternatively… if let myString = myOptionalNSString { if myString. length != 0 { print(“String is not empty.”) } }

How do you check if an object is NSNull?

We can use NSNull to represent nil objects in collections, and we typically see NSNull when we convert JSON to Objective-C objects and the JSON contained null values. Our preferred way to check if something is NSNull is [[NSNull null] isEqual:something] .

What is iOS null?

Null generally means an empty value in something. If you’re having an issue after the update, answering the following can help clarify the issue: Where are you seeing ‘null’ after updating? Which version of iOS is on your iPhone? You can find this in Settings > General > About > Version.

What is NSString?

A static, plain-text Unicode string object that bridges to String ; use NSString when you need reference semantics or other Foundation-specific behavior.

What is Nsnull?

A singleton object used to represent null values in collection objects that don’t allow nil values.

What is Nsdictionary?

An object representing a static collection of key-value pairs, for use instead of a Dictionary constant in cases that require reference semantics.

How do you fix NULL on iPhone?

Go into Settings, General, Usage, Manage Storage. Once there, find the “null” app and at the far right, touch the Right Arrow “>” to take you to the specific App detail screen.

How do you delete null apps on iPhone?

1 Answer

  1. View the apps you deleted.
  2. Find the app which about the same size with NULL app or version that match to the “Null” version.
  3. Download the app again.
  4. Remove it again and delete the cache.

What is an Nsrange?

A structure used to describe a portion of a series, such as characters in a string or objects in an array.

What is nsutf8stringencoding?

An 8-bit representation of Unicode characters, suitable for transmission or storage by ASCII-based systems.

Is it safe to use isKindOfClass to test for membership?

Generally isKindOfClass: is not safe to use to test for membership. If an instance returns YES for isKindOfClass: [NSString class], you know only that it will respond to all methods defined in the NSString class, but you will not know for sure what the implementation of those methods might do.

Iskindofclass a class cluster?

Both of these types are class clusters – but it seems from the documentation above that the danger lies in the answer to isKindOfClass: being too affirmative (answering YES sometimes when you really do not have a mutable array) whereas asking a question about simple membership in a cluster would still be valid. Is this assumption correct?

What is the difference between isKindOfClass and isMemberOfClass?

isKindOfClass: will return YES if the receiver somewhere inherits from the class passed as argument. isMemberOfClass: will return YES only if the receiver is an instance of the class passed as argument only, i.e. not including subclasses. Generally isKindOfClass: is not safe to use to test for membership.

Why does isKindOfClass return YES for [NSString]?

If an instance returns YES for isKindOfClass: [NSString class], you know only that it will respond to all methods defined in the NSString class, but you will not know for sure what the implementation of those methods might do. Someone might have subclassed NSString to raise an exception for the length method.