SwiftUI

Question 1

How to layout elements

Answer 1

Ways to Layout

- VStack { } - Vertical stack

- HStack { } - Horizontal stack

- ZStack { } - Back to front stack

Spacer() - Add equally divisible space to element

Question 2

How to allow UI to update a variable

Answer 2

Mark variable with @State

Prefix Variable name with $ when it needs to be read/write property

Question 3

How to display an alert

Answer 3

define alert in the declarative code

.alert( [title], isPresented: $[bool variable]) {
   Button([buttonTitle], action: [funcToCall])
}

Question 4

What does SwiftUI use for views

Answer 4

struct

Reasons

- Simpler and faster than classes
- Structs don't mutate over time - easier for SwiftUI runtime

Question 5

Show the code for a basic Swift UI screen

Answer 5

struct ContentView: View {
    var body: some View { 
        // Content goes here
    }
}

Question 6

How to make a color fill the screen

Answer 6

Multiple ways

ZStack {
    Color(.blue)
        .ignoresSafeArea()
    // Your content
}

OR

VStack(
    // Your content here
)
.frame((maxWidth: .infinity, maxHeight: .infinity)

Question 7

How to apply modifiers only under certain conditions ?

Answer 7

Use conditional inside the modifier

Button("Hello World") { 
}
.foregroundStyle(useRedText ? .red : .blue)

OR less efficient if /else

if cond { //define red button } else { //define blue button }

since it creates and destroys buttons rather than just modifying the property

Question 8

How to create a custom modifier ?

Answer 8

Create a struct that conforms to the

ViewModifier

protocol

struct ScreenTitle: ViewModifier {
    func body(content: Content) -> some View {
        content
            .font(.largeTitle)
            .foregroundStyle(.white)
            .padding()
            .background(.blue)
            .clipShape(.rect(cornerRadius: 10))
    }
}

Text("Hello World")
    .modifier(ScreenTitle())

To apply them directly without using .modifier(), you need to create an extension on View

extension View {
    func screenTitleStyle() -> some View {
        modifier(Title())
    }
}

Text("Hello world")
   .screenTitleStyle()

Question 9

How to use classes with SwiftUI ?

Answer 9

import Observability

mark classes with

@Observable

Question 10

How to present a SwiftUI sheet view ?

Answer 10

Define a @State variable set to false
define a Struct that contains the view you want to show
add a call to

.sheet(isPresented: $<boolVar>) { 
// sheet content / display the view }

Action needs to set <boolVar> = true</boolVar>

Question 11

How to you add ability to delete rows from a SwiftUI List ?

Answer 11

List has to be created using ForEach() and add

.onDelete(perform: removeItems) 
 // No params

Function removeItems has 1 argument that is an IndexSet of indexes to delete

Question 12

How to store a variable in User Defaults automatically ?

Answer 12

Use ```@AppStorage(“varname”) macro on your variable

Question 13

How to create performant scrolling lists in SwiftUI ?

Answer 13

Create a ScrollView(.vertical) that contains a LazyVStack

Question 14

In Swift UI, how to show a screen that “drills down” for more info

Answer 14

NavigationLink inside a NavigationStack

Question 15

In Swift UI, how to show an unrelated screen

Answer 15

add .sheet() section

Question 16

What is the equivalent of a CollectionView in Swift UI ?

Answer 16

LazyHGrid / LazyVGrid inside a ScrollView

Question 17

In Swift UI. how do I modify a variable across several screens ?

Answer 17

Declare the PARAMETER with @Binding
When changed in the subview, it reflects across all views

Question 18

In SwiftUI, how do you show an action sheet ?

Answer 18

Code works just like an alert.

.confirmationDialog("Change background", isPresented: $showingConfirmation) {
    Button("Red") { bgColor = .red }
    Button("Green") { bgColor = .green }
    Button("Blue") { bgColor = .blue }
    Button("Cancel", role: .cancel) { }
} message: {
    Text("Select a new color")
}

Question 19

In SwiftUI, how to show a placeholder if there is no data available

Answer 19

```ContentUnavailableView(“title text”, systemImage: “imagename”, description: Text(“instruct text”)
~~~

Question 20

How to make structs and classes sortable ?

Answer 20

• Add Comparable protocol
• Add compare func - example is for a User struct
  ~~~
  static func <(lhs: User, rhs: User0 -> Bool {
  lhs.lastName < rhsLastName
  }

Question 21

in SwiftUI, How do you get actual lat/long coordinates from Mapkit

Answer 21

Wrap your Map() in a MapReader() and use mapReader to convert position from local

~~~
MapReader { proxy in
Map(initialPosition: startPosition)
.onTapGesture { position in
if let coordinate = proxy.convert(position, from: .local) {
print(“Tapped at (coordinate)”)
}
}
}```

Question 22

Convert to MVVM

Answer 22

Create ViewModel class
Move @State variables to ViewModel
Remove @State and private from those vars
Create ViewModel variable as @State
Update SwiftUI vars to reference View Model

Question 23

How to handle long-press in SwiftUI

Answer 23

Use

.contextMenu { }

modifier

```.contextMenu {
Button(“Red”) { backgroundColor = .red }
Button(“Green”) { backgroundCOlor = .green }
}

Question 24

How to add swipe buttons to a List ?

Answer 24

Add

.swipeActions { }

modifier to add actions to right edge

Use .swipeActions(edge: .leading) { } to add actions to left edge

Question 25

How to implement search in SwiftUI ?

Answer 25

add modifier

.searchable(text: prompt:)

Also the item powering the list needs to update itself based on the search text.

Question 26

How to get icon on right-end of a List line ?

Answer 26

If you have 3 elements in the List item, SwiftUI doesn’t know how to format them.
Wrap all 3 in an HStack, and the 3rd element will shift to the right end of List element

Question 27

How to set keyboard button title for a TextField

Answer 27

Modifier .submitLabel(.next) or .done

Question 28

How to track and set focus ?

Answer 28

Define a hashable enum with values that cover all fields
Define field to hold focused field
@FocusState var focusedField: Field?

Add .focused() modifier
.focused($focusedField, equals: .name)

Question 29

How to show a password field ?

Answer 29

secureField.init()

Question 30

How do you pass a @State variable between views ?

Answer 30

Consuming view defines it as @Bnding var. Parent view passes $var to the consuming view

Question 31

How to configure a vqrible to be read / written from UserDefaults ?

Answer 31

Declare with @AppStorage(“keyname”)

Question 32

How to programatically scroll a scrollview ?

Answer 32

Wrap ScrollView() in a ScrollViewReader() and use SVR.scrollTo() inside a delayed main thread call

Question 33

How do I update SwiftUI data on a schedule ?

Answer 33

Wrap the updatable data in a TimeLineView(.everyMinute, …)

Question 34

How to handle flexible grid items when using LazyVGrid ?

Answer 34

Use

[GridItem(.adaptive(minimum: maximum:))]