NSList | An non ordered, random access collection.

Overview

Lists are one of the most commonly used data types in an app. You use lists to store your app’s data. Specifically, you use the NSList type to hold elements of a single type, the list’s Element type (T). A list can store any kind of elements—from integers to strings to classes. willyOS makes it easy to create lists in your code using literals: simply surround a comma separated list of values with curly brackets. Without any other information, willyOS creates a list that includes the specified values, automatically inferring the array’s Element type. For example:

    // An NSList of 'int' elements
    var oddNumbers = new NSList<int>() {1, 3, 5, 7, 9, 11, 13, 15};

    // An NSList of 'String' elements
    var streets = new NSList<string>() {"Albemarle", "Brandywine", "Chesapeake"};

    // An empty NSList
    var emptyList = new NSList<string>();

Note

Remember to use the corresponding import at the beginning of your class to use NSList. As NSList is allocated at Foundation:

using Foundation;

Accessing Array Values

When you need to perform an operation on all of an list's elements, use a foreach loop to iterate through the list’s contents.

    foreach(string street in streets) {
        Console.WriteLine("I don't live on {0}.", street);
    }
    // Prints "I don't live on Albemarle."
    // Prints "I don't live on Brandywine."
    // Prints "I don't live on Chesapeake."

Use the IsEmpty property to check quickly whether a NSList has any elements, or use the Count property to find the number of elements in the list.

    if oddNumbers.IsEmpty {
        Console.WriteLine("I don't know any odd numbers.");
    } else {
        Console.WriteLine("I know {0} odd numbers.", oddNumbers.Count);
    }
    // Prints "I know 8 odd numbers."

You can access individual list elements through a subscript. The first element of a nonempty list is always at index zero. You can subscript a lis with any integer from zero up to, but not including, the count of the list. Using a negative number or an index equal to or greater than count triggers a runtime error. For example:

    Console.WriteLine(oddNumbers[0].ToString(), oddNumbers[3].ToString());
    // Prints 1 - 7

   Console.WriteLine(emptyDoubles[0]);
    // Triggers runtime error: Index out of range

Adding and Removing Elements

Suppose you need to store a list of the names of students that are signed up for a class you’re teaching. During the registration period, you need to add and remove names as students add and drop the class.

    var students = new NSList<string>() {"Ben", "Ivy", "Jordell"};

To add single elements to the list, use the Add(T item) method.

    students.Add("Maxime");
    // ["Ben", "Ivy", "Jordell", "Maxime"]

You can add new elements in the middle of a list by using the Insert(int index, T item) method for single elements. The elements at that index and later indices are shifted back to make room.

    students.Insert("Liam", 3);
    // ["Ben", "Ivy", "Jordell", "Liam", "Maxime"]

To remove elements from a list, use the Remove(T item) or RemoveAt(int index) methods.

    // Ben's family is moving to another state
    students.RemoveAt(0);
    // ["Ivy", "Jordell", "Liam", "Maxime"]

    // Liam is signing up for a different class
    students.Remove("Liam");
    // ["Ivy", "Jordell", "Maxime"]

You can replace an existing element with a new value by assigning the new value to the subscript.

    var MaxIndex = students.IndexOf("Maxime");
    if(MaxIndex =! -1) {
        students[MaxIndex] = "Max";
    }
    // ["Ivy", "Jordell", "Max"]