The NSMutableArray Class

The NSMutableArray is a class of the Foundation Framework and it enables you to instantiate (create) mutable array objects. An NSMutableArray can hold more than one objects (elements) at a time. An NSMutableArray is also referred to as an ordered collection of objects. The NSMutableArray class is a subclass of the NSArray superclass and it inherits all methods of that class.

nsmutablearray

Here are some general information you should know about the NSMutableArray class:

  • Instances (objects) of the NSMutableArray class are mutable. This means once you’ve instantiated and initialize an NSMutableArray, you can add or delete elements from it.
  • Elements of a mutable array must be an Objective-C object, primitive C types, like int, float, etc. are not allowed.
  • Indexes of a mutable array are zero base as shown in this image.
    nsarray_index
  • The last element added to a mutable array must always be nil; thus signaling the end of the mutable array.
To practice source code presented in this lesson, you should download and unzip this file.
project_icon_codepractice
Launch the project (CodePractice.xcodeproj) and enter code in the viewController.m file’s buttonTapped method, then click the “Click Me” button to execute the method’s code.

Instantiate and Initialize an NSMutableArray Object

Here is how you instantiate and initialize a mutable array object with ten string objects, and display the fifth element in the UITextField control. Don’t forget that the keyword nil, signals the end of the mutable array.

NSMutableArray *fruits = [NSMutableArray arrayWithObjects:
@"Avocado",
@"avocado.png",
@"Mango",
@"mango.jpg",
@"Water Melon",
@"watermelon.png",
@"Passion Fruit",
@"passiongfruit.jpg",
@"Bread Fruit",
@"breadfruit.jpg",
nil];

self.inputBoxOne.text = [fruits objectAtIndex:5];

Output
watermelon.png

Common Methods of The NSMutableArray

The addObject: Method

This method is used to add a new element at the end of a mutable array.

Code Output 
// Add two new elements in the mutable array
[fruits addObject:@"Banana"];
[fruits addObject:@"banana.jpg"];

// Convert the mutable array to a string variable, then assign it to a string object
NSString *stringFruits = [fruits componentsJoinedByString:@"\n"];

// Assign the stringFruits variable to the UITextView control
self.outputBox.text = stringFruits;
nsmutablearray_fig2

The atIndex: Method

This method adds an element at a specific index in a mutable array, as demonstrated below.

Code Output 
// Add an element at index 2
[fruits insertObject: @"Guava" atIndex:2];

self.outputBox.text = [fruits componentsJoinedByString:@"\n"];
nsmutablearray_fig3

Notice how elements of the array were shifted down to make room for the new element.

The removeObjectAtIndex: Method

This method removes an element at a specific index of a mutable array.

Code Output 
// Remove element, passionfruit.jpg
[fruits removeObjectAtIndex:7];

self.outputBox.text = [fruits componentsJoinedByString:@"\n"];
nsmuatablearray_fig4

The removeLastObject Method

This method does exactly what it say, remove the last element in a mutable array.

Code Output 
// Remove breadfruit.jpg from the mutable array
[fruits removeLastObject];

self.outputBox.text = [fruits componentsJoinedByString:@"\n"];
nsmutablearray_fig5

The removeAllObjects Method

This method does exactly what it says, it remove all objects (elements) from a mutable array.

Code Output 
[fruits removeAllObjects];

self.outputBox.text = [fruits componentsJoinedByString:@"\n"];
nsmutablearray_fig6