Explore
For Enterprise
Join for Free
Log In

艺术与人文
商务
计算机科学
数据科学
信息技术
健康
数学和逻辑
个人发展
物理科学与工程
社会科学
语言学习
學位
證書

瀏覽 Coursera 的全部課程

瀏覽
搜索
企業版
登錄
免費加入

Methods, Arrays and Control Flow Differences

Loading...

Swift 程序设计入门

多伦多大学

3.9（1,252 個評分） | 56K 名學生已註冊

課程 1（共 4 門，使用 Swift 进行 iOS App 开发專項課程）

Introduction to Swift Programming is the first course in a four part specialization series that will provide you with the tools and skills necessary to develop an iOS App from scratch. By the end of this first course you will be able to demonstrate intermediate application of programming in Swift, the powerful new programming language for iOS. Guided by best practices you will become proficient with syntax, object oriented principles, memory management, functional concepts and more in programming with Swift. This course is unique in its dedication to teaching Swift programming. With new features and capabilities you will be at the forefront of writing iOS apps. Currently this course is taught using Swift 2. The team is aware of the release of Swift 3 and will be making edits to the course in time. Please be aware that at this time the instruction is entirely with Swift 2. Please note that to take part in this course (and the full specialization) it is required to have a Mac computer and, though not required, ideally an iPhone, iPod, or an iPad. NOTE: This course has been designed and tested (and content delivered) on a Mac. While we are aware of hacks and workarounds for running Mac in a virtual machine on windows we do not recommended a PC. We hope you have fun on this new adventure.

查看授課大綱

您將學習的技能

iOS App Development, Syntax, Computer Programming, Swift (Programming Language)

審閱

3.9（1,252 個評分）

5 stars
601 ratings
4 stars
314 ratings
3 stars
132 ratings
2 stars
87 ratings
1 star
118 ratings

LO

Jul 29, 2016

Amazing course with awesome material.\n\nA great way to start learning the basics of Swift and getting to know people that have the same aspiration of learning new stuff.

AC

Jun 25, 2016

It's very easy. On the other hand the teachers do not do very deep and you need to do a lot of selfstudy. Would not recommend for the ones without basic knowledge of CS.

從本節課中

OPTIONAL - Swift vs Objective C

OPTIONAL - In this module we compare some of the differences between Swift and Objective C programming languages. Join us as we migrate those of you familiar with Objective C to the world of Swift. Hopefully you find programming in Swift fast, easy and interactive.

Introduction to the Module1:10

Files, Naming and Class Differences5:44

Types and Initializers Differences9:29

Methods, Arrays and Control Flow Differences10:07

Properties, Getters and Computed Properties Differences6:40

Instantiating Objects and Calling Methods Differences16:18

教學方

Parham Aarabi
Professor

腳本

[MUSIC]

Okay now that again we’ve gone one more step in defining the city classes and

most objectives we see in Swift, what is next?

What else can we showcase the difference between these two languages?

>> So we’re going to show something a bit more interesting, a function.

A method of a class, of our city class.

And we're also gonna create our country class which we had put off till now.

So I mean, what method makes sense for a city?

None of them.

We have to creat our country class.

>> Yeah. So, that's right.

So, the city class is pretty basic.

It just holds a population and a name.

I mean, we could add more stuff to that at some point if we wanted to.

But, for now, we'll just keep it straightforward.

It's just a data dump for our names and populations.

So, but we're gonna store those city classes in a country.

Country's gonna hold a bunch of cities.

So it's gonna have an array of cities, and the country itself has a name as well.

So the country has to initialize itself with a list of cities.

And then we can do things on that like find the biggest city, or

find the particular city with a particular name.

So we'll need to create a method on the country to kind of search through its

cities for the kind of city that we want.

We could, you know, do all sorts of stuff with the country object eventually.

>> Yeah, and so

I'm basically going through the same things we've done already in this module.

It's a good, use this as a nice review,

but in here we're gonna create a UTCountry.

And again, the UT prefix, to make sure that our country is our country.

>> Yeah, so we don't override somebody else's country class that was maybe

created somewhere else.

>> Yes, and we also don't want anyone else overriding our country class.

>> Yeah, eventually. >> That guy is very important.

And there is one interesting thing, I guess, here which is the cities array.

And you'll see very soon right now that here,

we're using an array of City, which we've seen before.

And it's a Value type, holding an array of cities, where here, we're

using an NSArray, which is Objective-C's class for any kind of array really.

And it can store anything you want as long as it's an object.

>> Yeah, that's right.

And are you doing assign there, or strong?

>> It should be strong.

>> I think it's strong [LAUGH], cuz array is also a reference to an array,

not an actual value of an array.

Really that's important that the Objective-C collection types can store

any Objective-C object.

But they can't store numbers, it's just very interesting.

So you can create an array of integers in Swift.

Because that's totally, an integer, is a type that can be stored in an array.

But in Objective-C,

you would have to box that integer into an object, like a NS number.

Or some kind of like specialized object for storing that number.

You can't store regular integers in an array.

You can only store objects, basically anything that would

be referenced by an ID or a class star kind of variable.

>> Now as you were talking, Jack, you were talking a little ahead.

So perhaps first of all, that point is very useful.

And it shows that Swift, a lot of things have become perhaps a little simpler and

more obvious for users who've used Java, for example, before.

But what did you just type?

So- >> Yeah, so here in object we define

the country in Swift, and here is the country in Objective-C.

And it's very similar to the city except for what we were just talking about,

the rate hike, which is many cities which is very different from the city,

city array we see in Swift.

And then everything else is pretty much the same as the city itself.

And here we have the initializer,

which now takes in a city instead of a population.

>> So, essentially the code on the right is the exact implementation in Objective-C

on the Swift code out on the left.

>> Mm-hm.

Which we covered in the previous section.

So, here we're going to add a method.

So, we were going to maybe find a city, return a city by name?

>> Yeah. So, maybe my user taps a city in a list,

and then you wanna get more information about that city,

maybe the population of the city.

So you have to go to your model object that we're doing here and

find that particular city.

And we would look it up by name,

which would be the easiest way right now, I guess.

>> That makes sense.

So it would be find city with name,

and then we pass in name string.

There are probably better ways in Swift to do this,

as we covered in the standard library, ways you can search through a string.

But here to show comparisons with Objective-C, we're just going to iterate

through the array and do string comparison on all the names.

>> And ultimately, if it works it works, right?

>> Yeah. >> [LAUGH] You can get fancy with

a single line of code.

But sometimes a for loop is just less mental gymnastics, so [LAUGH].

>> I agree. >> Yeah.

>> Oh, and just something that we totally missed here.

>> Yep. >> This is the return bad, return type.

This should give you a city, but an optional city because it might not,

the name you're passing may not be in our cities already.

So if we find it we're gonna return the city, if we don't find it,

we're gonna return nil.

>> Like, if I'm looking for Tokyo but my country is Canada.

You would wanna return nil just to indicate that that city doesn't exist

in Canada basically.

>> Yes.

And we covered that in our optionals, so you should know that.

And in Objective-C, the same function is gonna look a bit weird.

FindCityWithName, my bad,

it's called a UTCity.

[LAUGH] And we're going to do a similar thing.

>> And don't forget the brackets there.

[LAUGH] You're doing pretty good switching back and forth and

talking at the same time.

It's pretty impressive.

>> [LAUGH] Name is equal to string.

And that's a very clear way of specifying who you want.

[LAUGH] Return city.

>> So if we just said if city equals name,

what we would be comparing there would be the pointers, and that would may or

may not work but it's not what we're actually trying to test.

We want to test the quality of the actual string, so

in Objective-C there is a function, or a method,

that is called isEqualToString which will actually compare the two strings.

In Swift, because string is a value type, when you say equals equals or compare, you

actually are comparing the actual value of the string between the two symbols there.

>> Yeah, like we covered in value type versus reference types.

When you compare value types, you want to compare their meaning.

If they represent the same thing, then they're just saying, object,

they don't have to be the actually same, created at the same time.

Where as in object, if you're comparing the pointers,

then they're pointing to the same location in memory, which is the same exact object.

>> Yeah, which is not we wanted to compare,

because that name could come from anywhere.

Somebody could have typed it in, who knows, right?

So we wanted to compare the actual string, not the pointers.

Objective-C, you have to be careful about that distinction here.

>> Mm-hm.

So is there anything that looks weird to you here, Parham?

>> I think it's fairly straightforward.

The one observation is that, again, look at how simpler it is to

create the same function or the same effect in Swift versus Objective-C.

So, really, Swift does make life a lot easier to use.

>> Yeah. We're not even done with Objective-C yet

because right now this method is only in our implementation.

So, no one else can even see it.

>> One nice thing about the Swift one as well is in the method signature there

it indicates that it may return nil.

So, anybody who looks at that and tries to use that function has to test for nil.

Where as, if somebody naively uses our Objective-C version, they may not realize

it could return nil and they may get into trouble at some point later in their code.

>> Yes because in this case it makes sense to return optional.

In other functions where it doesn't make sense to return optional, for

example, if we ask for the city with the most people and

it's always gonna be a city with the most population, right?

>> Unless there's no cities.

>> Unless there's no cities, which we're not gonna consider.

Because our city.

Well, I guess that's true.

>> I guess there could be a country with no cities.

>> Yes. >> Antarctica maybe.

>> [LAUGH] Is that a country?

>> No. Let's not get into geopolitics.

>> Yes.

But say there was no way it could do that.

Then in Swift,

we could let the user of the function know by not returning an optional.

Whereas, in Objective-C, we would still return it as point utility, a UTCity.

Which, even though it could never be nil, it could be nil [LAUGH].

We could say that nil- >> Yeah, we could make a mistake in our

code, for example, and- >> And it'll be nil.

>> The compiler wouldn't catch it, for example.

Whereas, Swift, if we If we remove that return nil, for example, at the bottom

there, it's gonna give us, it's actually gonna warn us, you know, that

missing return, so- >> Yes, yep, very good points.

And again, so back to Objective-C, which is already a bit more code than Swift is.

We then have to copy this function.

We have to declare this function in the header file to make sure

that other parts of our code can see it.

探索我們的目錄

免費加入並獲得個性化推薦、更新和優惠。

Coursera 致力於普及全世界最好的教育，它與全球一流大學和機構合作提供在線課程。

© 2019 Coursera Inc. 保留所有權利。

通過 App Store 下載

通過 Google Play 獲取

Coursera
關於
管理團隊
工作機會
目錄
證書
MasterTrack™ 證書
學位
企業版
政府版

社區
Learners
Partners
Developers
Beta Testers
Translators

連接
博客
Facebook
領英
Twitter
Instagram
YouTube
技術博客

更多
條款
隱私
幫助
內容訪問
媒體
聯繫我們
目錄
附屬公司