What is the difference between NSDictionary and NSMutableDictionary?

Main Difference is: NSMutableDictionary is mutable( can be modified) but NSDictionary is immutable (can not be modified).

What is a NSDictionary object?

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

What is difference between dictionary and NSDictionary?

4 Answers. Dictionary is a native Swift struct. NSDictionary is a Cocoa class. They are bridged to one another (within the usual limits), as the docs explain very clearly and fully.

How do I create an NSDictionary in Objective-C?

Objective-C Language NSDictionary

1. Create# NSDictionary *dict = [[NSDictionary alloc] initWithObjectsAndKeys:@”value1″, @”key1″, @”value2″, @”key2″, nil];
2. NSDictionary to NSArray.
3. NSDictionary to NSData.
4. NSDictionary to JSON.
5. Block Based Enumeration.
6. Fast Enumeration.

Is NSDictionary ordered?

NSDictionary keys & values are not ordered.

Is NSDictionary thread safe?

In general, the collection classes (for example, NSMutableArray , NSMutableDictionary ) are not thread-safe when mutations are concerned.

How do you get the key in NSDictionary?

3 Answers

1. To get the first key only is NSString *firstKey = [dict allKeys][0]; – Mazen Kasser.
2. @MazenKasser firstObject is a safer solution – in case if the dictionary doesn’t have any keys the app won’t crash: dict.allKeys.firstObject; – Islam.
3. the order of keys returned by allKeys is undefined…

What is NSMutableArray Objective C?

The NSMutableArray class declares the programmatic interface to objects that manage a modifiable array of objects. This class adds insertion and deletion operations to the basic array-handling behavior inherited from NSArray . NSMutableArray is “toll-free bridged” with its Core Foundation counterpart, CFMutableArray .

Why is UIKit not thread-safe?

It’s a conscious design decision from Apple’s side to not have UIKit be thread-safe. Making it thread-safe wouldn’t buy you much in terms of performance; it would in fact make many things slower. And the fact that UIKit is tied to the main thread makes it very easy to write concurrent programs and use UIKit.

Is Dictionary thread-safe Swift?

Dictionaries in Swift are not thread safe , they lead to wierd crashes which are very hard to debug. This class solves this problem by using a dictionary whose accesses are made thread safe by using a concurrent queue with a barrier.

What is nsnull in Java?

NSNull represents nothing with an actual object rather than a zero value like nil or NULL. NSNull is used throughout Foundation and other frameworks to skirt around the limitations of collections like NSArray and NSDictionary not being able to contain nil values.

Can a key or value be nil in NSDictionary?

Neither a key nor a value can be nil; if you need to represent a null value in a dictionary, you should use NSNull. NSDictionary is “toll-free bridged” with its Core Foundation counterpart, CFDictionary. See Toll-Free Bridging for more information on toll-free bridging.

What is the difference between null and +null?

nil is an object pointer to nothing. Although semantically distinct from NULL, they are technically equivalent to one another. On the framework level, Foundation defines NSNull, which defines a class method, +null, which returns the singleton NSNull object.

What is null in Objective-C?

In Objective-C, there are a few different varieties of nothing: NULL, nil, Nil, and NSNull. C represents nothing as 0 for primitive values and NULL for pointers ( which is equivalent to 0 in a pointer context). The only time you see NULL in Objective-C code is when interacting with low-level C APIs like Core Foundation or Core Graphics.