How to Create a Dictionary

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En provenance du cours de University of California, Irvine

Toward the Future of iOS Development with Swift

71 notes

University of California, Irvine

Toward the Future of iOS Development with Swift

71 notes

Cours 5 sur 6 dans Specialization iOS Development for Creative Entrepreneurs

An introduction to the Swift programming language. This will prepare you for more extensive iOS app development and build a foundation for advanced iOS development topics. Upon completing this course, you will be able to: 1. Associate the relationship of Swift and Objective-C and their use in iOS and Mac (OS X) programming 2. Develop the ability to read and write Swift code 3. Distinguish how both programming languages can be used together in applications 4. Demonstrate how to write applications entirely in Swift with the help from several iOS programming samples 5. Determine how Swift can be used for development on new platforms such as Apple Watch and Apple TV 6. Create a working client-server iPhone application with location services that you can add to your portfolio.

À partir de la leçon

Introduction to Swift

In this first week, you will get a first look at the programming environment and the Swift programming language. If you have taken the “Foundations of Objective-C App Development” Course in this Specialization, some of this content may be familiar. Students who have not taken that course - no need to worry - you will receive a full introduction to become familiar with programming for iOS or Mac OS X as if Swift is your first programming language.

How to Create a Dictionary8:25

Using and Modifying Dictionaries Part 18:07

Using and Modifying Dictionaries Part 26:04

Properties of Dictionaries3:51

Rencontrer les enseignants

Justin-Nicholas Toyama
UCI Extension Instructor
Lead iOS Developer at Smilefish Corporation
Frank Ayars
UCI Extension Instructor
CTO and Director of Software Development at Smilefish Corporation
Ralf Brockhaus
UCI Extension Instructor
Founder and CEO at Smilefish Corporation

[MUSIC]

All right, so welcome to Collection and Functions.

This is Part II: Dictionaries.

So here's what we'll cover.

We'll learn, what is a dictionary.

How do we create dictionaries?

How do we use and modify the values inside of dictionaries?

And so, let's get right into it.

A dictionary is a collection or a list of key-value pairs.

The order of these key-value pairs is not guaranteed.

So keep in mind that unlike an arrays which is an ordered list,

we're going to be asking for the values out of this dictionary in

a different manner rather than depending on the order in which

those values are contained in the dictionary.

Each value is paired with a key so we call these key value pairs and

that's how our information is stored in the dictionary.

And we query the dictionary for the values it contains by key name.

So a lot of times, the key name is a string, and

that's what we'll be doing today.

It doesn't have to be, but that's very common usage.

So here's a new playground for dictionaries.

Let's look at how do we create a dictionary?

So how do we create a dictionary?

We can declare mutable dictionaries using the var keyword,

declare immutable dictionaries using let,

we can explicitly type the dictionary or again rely on Swift's type inference,

and we can also create dictionaries with multiple syntaxes.

Very much like we saw, but there's many different ways to create arrays.

All right, so let's look at our dictionary's playground.

How do we create a dictionary?

The following four lines are essentially equivalent.

All right, so I have varred my dictionary and

have created this dictionary using the dictionary type symbol.

And inside of angle brackets, I have on the first type before the comma,

I have the type that will be accepted for my keys and my key value pair.

And to the right of the comma, I have the type that will be accepted for

the values for my key value pair.

This type which is dictionary key type string, value type string,

will be applied for all of the key value pairs in my dictionary.

So I won't be able to have one key value pair that's string-string and

another key value pair that's String some other type.

They all have to be key string and

value string because of the way they have declared this dictionary.

I can initialize this dictionary using the dictionary literal

syntax of square bracket, a colon enclosed with square brackets.

So we're used to arrays.

We see square brackets and comma separated values.

With dictionaries, we'll have again square brackets and

comma separated key value pairs.

How do I know where a key value pair is?

Look for a colon, all right.

So we'll have something colon something, comma, another something, colon,

another something.

That's how you can visually distinguish between an array and a dictionary.

All right, here's my second dictionary.

Again, I say of type Dictionary, String,

String inside of angle brackets.

But notice that here I'm immediately setting the value of my

second dictionary using the assignment operator, and

then I put the type followed by open, closed parentheses which

initializes this dictionary for me with the specified key value types.

Okay, the third dictionary here, var myDictionary equals,

you got a different way, different syntax but same thing going on.

We're initializing another empty dictionary with the keys

being of type string and the values being of type string.

And then I set that equal to NOT, NOT dictionary.

And last, my fourth dictionary, I immediately set it equal to the type

followed by the open close parentheses which is, we can read as, an end.

So dictionary of type string string then end.

All right so basically, In taxes here we can use the dictionary key word followed

by the key types and value types instead of angle brackets.

Or use the dictionary little tax which is the open closed

square brackets with a colon to separate our key value pairs and

a comma separating our, Comma is separating the key value pair.

Okay, we can also initialize and populate the dictionary all in one line of code.

So here I have three planets to extend upon our solar system example.

Here we have Mercury of type [String : AnyObject?].

Now I'm going to put different information about

Mercury inside of my dictionary here.

And all of these pieces of information may not have the same data types.

That's why I'm using this generic type AnyObject.

And also I may not have a value for every piece of information,

every type of information for all of the planets in this example.

So we'll make it an optional type, any object's question mark.

We can read that in English as optional any object.

All right so now I've set what the type of the Mercury dictionary is.

Now I'm going to populate it right away.

So I say equals, open square bracket, the string name,

that's my key, from my first key value pair, colon, and

the string mercury, for the value in my first key value pair.

I also want to know in which order the planets come in our solar system.

You know the orders starting with the sign in the middle.

So, I'll create another key value pair.

The name of the second key value pair is the string order and

the value of that is 1.

So, I'll use that same syntax to create a few more planets.

We have Venus and Earth and Mars.

Notice with Earth, the type of the dictionary can be inferred.

We can remove the type and

the compiler will do its best to guess what

the type of the earth dictionary is.

Now to make this code a little bit safer for later usage in our example,

we'll just make sure that all of our planets are explicitly typed that way.

We don't have to do any kind of special do of type casting

if we come across a planet for which we didn’t explicitly type it.

All right, and I'm not going to put in all of the planets in the solar system and

all of their moons because it's a little bit too much for this example.

So we'll just pretend that we've put in the rest of the planets upto Neptune.

And for Neptune, so that we have some more data to work with,

I've listed out the 14, I think, different moons of Neptune.

All right, so for Neptune, we know some more information,

the name of it, the name of the planet, what the moons of the planet are,

and the planet's order in the solar system.

[MUSIC]

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