Swift provides three primary collection typesknown as arrays, sets, and dictionaries, for storing collections of values. Arrays are ordered collections of values. Sets are unordered collections of unique values. Dictionaries are unordered collections of key-value associations. Arrays, sets, and dictionaries in Swift are always clear about the types of values and keys that they can store. This means that you cannot insert a value of the wrong type into a collection by mistake. It also means you can be confident about the type of values you will retrieve from a collection.
For more about generic types and collections, see Generics.SwiftUI TableView / List Tutorial
If you create an array, a set, or a dictionary, and assign it to a variable, the collection that is created will be mutable.
If you assign an array, a set, or a dictionary to a constant, that collection is immutableand its size and contents cannot be changed.
It is good practice to create immutable collections in all cases where the collection does not need to change. Doing so makes it easier for you to reason about your code and enables the Swift compiler to optimize the performance of the collections you create. An array stores values of the same type in an ordered list. The same value can appear in an array multiple times at different positions.
You can also write the type of an array in shorthand form as [Element]. Although the two forms are functionally identical, the shorthand form is preferred and is used throughout this guide when referring to the type of an array. Note that the type of the someInts variable is inferred to be [Int] from the type of the initializer. Alternatively, if the context already provides type information, such as a function argument or an already typed variable or constant, you can create an empty array with an empty array literal, which is written as  an empty pair of square brackets :.
You pass this initializer a default value of the appropriate type called repeating : and the number of times that value is repeated in the new array called count :. You can also initialize an array with an array literalwhich is a shorthand way to write one or more values as an array collection. An array literal is written as a list of values, separated by commas, surrounded by a pair of square brackets:.
The example below creates an array called shoppingList to store String values:. Because this particular array has specified a value type of Stringit is allowed to store String values only. Here, the shoppingList array is initialized with two String values "Eggs" and "Milk"written within an array literal.
The shoppingList array is declared as a variable with the var introducer and not a constant with the let introducer because more items are added to the shopping list in the examples below. In this case, the array literal contains two String values and nothing else. The initialization of shoppingList could have been written in a shorter form instead:. Because all values in the array literal are of the same type, Swift can infer that [String] is the correct type to use for the shoppingList variable.In order to handle dynamic items, you must first tell SwiftUI how it can identify which item is which.
This is done using the Identifiable protocol, which has only one requirement: some sort of id value that SwiftUI can use to see which item is which.
For example, you might create a Restaurant struct that says restaurants have an ID and name, with the ID being a random identifier just so that SwiftUI knows which is which:. Next you would define what a list row looks like. Finally we can create a list view that shows them all.
This means creating some example data, putting it into an array, then passing that into a list to be rendered:. That creates a list from the restaurants array, executing the closure once for every item in the array.
Each time the closure goes around the restaurant input will be filled with one item from the array, so we use that to create a RestaurantRow. Sponsor Hacking with Swift and reach the world's largest Swift community! Articles Learn Start Here. Start Here. Browse Swift Courses Book bundles. About Hacking with Swift. Was this page useful? Let us know! Link copied to your pasteboard.By this part of the course, you've already built a couple of different SwiftUI screens using a bunch of SwiftUI views.
The most popular apps like Instagram, Twitter or Reddit all show a big list of stuff on their main screen. You'll learn this by building a contacts screen. This screen will show all of the users your current user can chat with. By the end of this part, you'll have a screen that looks like this:. Before you can build that screen, though, you first need a way to navigate to it. Let's get started! You can always find the finished project code on GitHub.
You'll start by creating a new SwiftUI view file for your contacts screen and naming it ContactsView. Change the struct to the following:. So far it doesn't show much — you'll take care of that later. For now, let's add a way to navigate to this view. Open LoginView. If you run the app now and click the login button, you'll navigate to the view.
Now we can fill it up with contacts! First, we'll lay some groundwork on SwiftUI lists. Much like Group or VStacka List is a sort of wrapper around a bunch of child views.
It hugs all of its children in a tight embrace and positions them on the screen, one below the other, with separators, paddings, a scroll view and everything else you'd expect from a list. Apple is an environmentally conscious company, after all, so cells are recycled. Instead of loading all of your rows at once, SwiftUI will only take up memory for the rows that are currently visible.
As you scroll, the rows that disappear are not destroyed, but instead, go into a pool of deactivated rows. When the list needs a new row, instead of allocating one, it will take one from the pool.
When the list takes a row from the pool, it will apply any necessary changes to its views text values, images, etc. This gives the appearance of having many rows, while in reality only a couple are ever loaded at once.
SwiftUI, list with indices without enumerated
All this is to say that List s are very fast and memory-efficient, regardless of how many rows there are in the list. In UIKit, you'd probably first create a table view and then think about placing items in that table. The component-based nature of SwiftUI means you'll have to reverse your thinking: Start from smaller views and work your way up.
That's why you'll first create the view for each row in your list and only then begin assembling the contacts screen. Note : On websites like StackOverflow, you'll often see people suggesting you replace List with a ScrollView and a ForEach view to achieve a desired look. In some cases, this works well. However, ScrollView will load all the items at once. If you have a lot of items, a plain scroll view will be much less efficient than a List! Before we create our items, we need a model struct to house information about each contact.
Create a new plain Swift file called Contact. Change the contents to the following:. You'll notice Contact conforms to Identifiable.
To easily show an array of items in a list, those items need to each have a unique identifier.One of the common things we want to display with SwiftUI are lists of our models. The basics of it are pretty easy, you just need to use a ForEach view. This works out of the box assuming your model is Identifiable. Otherwise you will need to pass a second argument to the ForEach giving a KeyPath to the id.
It gets a little trickier when you want to display no only your data but also its position on the list. You may try the correct solution directly, but I would like to show here the different options we have and discard many of them, since they can provoke errors and even crashes. Sadly those are the ones you will find recommended online so always be careful. Don't even take my word for granted!
One of the obvious ways of doing it is using the enumerated function on your collection. This will return a new collection with a tuple of the element and its offset.
The first problem we encounter with this approach is that we need to provide an ID, since the tuple of the collection is not Identifiable. The issue here is that ForEach needs a RandomAccessCollectionpresumedly to access directly specific elements of the collection to reload only those that change.
But when using enumerated we get back an EnumeratedSequencea sequence that doesn't provide random access. Still, it helps us understand what's going on. The reason this satisfies the compiler is because the reversed function returns an Arraywhich is a RandomAccessCollection. One correct approach is to take the enumerated sequence and consume it immediately to create an array. Remember, any performance claim needs to be backed with real data, which I don't have, so don't take this as pure truth but To create that array the sequence needs to be iterated fully, so on big datasets it could be noticeable.
And remember that this code is inside SwiftUI View body function, so it will run quite often. You can probably live with this for a while if you control your data set and is not that big, you may even want to make it nicer with some extension on collection that gives you directly an enumerated array or even a fancy custom initialiser in the ForEach.For data you have to retrieve from somewhere else, this becomes a little more complicated.
With a List and a ForEach block, you get 2 options for what you can pass in. You can either pass in a Range think for 1 to 5or a RandomAccessCollection. We could try to hide the logic that gets the data from the API inside of here. NSFetchedResults implement this interface, too. The variable here that starts to concern me is the endIndex.
But what about an API that is paginated? I updated some old code to print out the end index when the view loads. CoreData knows the total amount of elements loaded when the view first loads.
Hopefully we can update the endIndex without causing the list to reset. However, we can use the. This worked a lot better than I expected. This should be an easy update. We can check if the post that we pass in matched one of the last X elements. This can be done in the shouldLoadMorePosts function:. It returns a paginated list of articles, so this is perfect for this demonstration.
In a previous post, I talked about how you can asynchronously load data from an API. Using a very similar technique, we can hit our API to get our news data.
The first thing we need to keep track of is the next page we need to load. This API is paginated, and the first page we retrieve will be page 1. We can set a flag before we start our call. Once everything is processed, we can pass the list to the main thread to update our ObservedObject s.
The dark mode beta is finally here.
How to edit selected item in list in SwiftUI
Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Learn more. Asked 5 days ago. Active 5 days ago. Viewed 25 times. Brejuro Brejuro 2, 5 5 gold badges 21 21 silver badges 43 43 bronze badges.
What is the View type you are using? Also, what do you mean by Does not work? Does it not compile? Sam Sorry, to be clear the zIndex does not take effect, the "row" I'm forcing to the top zIndex does not actually go to the top. My guess would be a bug in SwiftUI — maybe try sticking Group s everywhere and see if it has an effect? Active Oldest Votes. Sign up or log in Sign up using Google.
Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown.
The Overflow Blog. Socializing with co-workers while social distancing. Podcast Programming tutorials can be a real drag. Featured on Meta.
Subscribe to RSS
Community and Moderator guidelines for escalating issues via new response…. Feedback on Q2 Community Roadmap. Technical site integration observational experiment live on Stack Overflow. Triage needs to be fixed urgently, and users need to be notified upon…. Dark Mode Beta - help us root out low-contrast and un-converted bits. Related Hot Network Questions. Question feed.In order to handle dynamic items, you must first tell SwiftUI how it can identify which item is which.
This is done using the Identifiable protocol, which has only one requirement: some sort of id value that SwiftUI can use to see which item is which. For example, you might create a Restaurant struct that says restaurants have an ID and name, with the ID being a random identifier just so that SwiftUI knows which is which:. Next you would define what a list row looks like. Finally we can create a list view that shows them all.
This means creating some example data, putting it into an array, then passing that into a list to be rendered:. That creates a list from the restaurants array, executing the closure once for every item in the array. Each time the closure goes around the restaurant input will be filled with one item from the array, so we use that to create a RestaurantRow.
RevenueCat makes it simple. With their open source SDKs, you can painlessly implement subscriptions for your app in hours, not months.
Explore the docs to learn more. Sponsor Hacking with Swift and reach the world's largest Swift community! Articles Learn Start Here. Start Here. Browse Swift Courses. About Hacking with Swift. Was this page useful? Let us know! Link copied to your pasteboard.