Swift and SwiftUI Learnings

This is a living article. It’s not finished, and it’s written as I learn. It may be updated over time.

1. Don’t download Xcode from the App Store. Xcode is huge and takes a long time installing from the App Store. Instead, download it from Apple directly. This way you can see a progress bar and it’s way faster.

2. This is a struct (I would call it a dict in JS):

   struct Person {
     var firstName = ""
     var lastName = ""
   }
   

3. Difference between variables and properties. Difference between functions and methods.

   Variables inside a Struct are called Properties

   Functions inside a Struct are called Methods

4. SwiftUI seems far easier to create an UI than the other methods. (I am by no means an expert on this topic)

5. This is a view and the basic building block of building an UI with SwiftUI.

   struct ContentView: View {
       var body: some View {}
   }
   

6. A View ist just a structure (with a body property set). This body property is then rendered.

7. The Body Property of a View is a computed Property, meaning it will be generated from the Code inside.

   struct ContentView: View {
       var body: some View {
           return ZStack {
   
           }
       }
   }
   
   // the return keyword can be omitted if it's only one line of code
   struct ContentView: View {
       var body: some View {
           ZStack {
   
           }
       }
   }
   

8. Why is there a : View in the Structure Declaration? The Data Type for the ContentView is ContentView not View. This means it follows a Protocol (in this Case View Protocol)

9. some View means then actually: Returns some data type which conforms to the View Protocol.

10. Trailing Closure Shorthands. If we look at the declaration of an init function) (e.g. of a Vstack). It looks like this:

    init(alignment: HorizontalAlignment = .center, spacing: CGFloat? = nil, content: () -> Content)
    

    So why can we do this:

    VStack {
    
    }
    

    This is a short hand for this:

    VStack(content: {
    })
    

    this works for the last parameter.

11. View Modifiers: methods, that create a new view from an existing view e.g. .font(.title)

12. Modifiers have a deterministic ordering:

    Text("test text")
        .background(Color.green, cornerRadius: 10)
        .padding(.all)
    

    The padding will not have a green color. But in this case, it will:

    Text("test text")
        .padding(.all)
        .background(Color.green, cornerRadius: 10)
    

    Shamelessly stolen from an WWDC Talk

13. Conditions and Modifiers: Push as much conditions as possible into modifiers, this will help SwiftUI better determine default animations

    if bool {
        AppIcon()
            .rotationEffect(.degrees(180))
    } else {
        AppIcon()
    }
    

    instead do:

    AppIcon()
            .rotationEffect(.degrees(bool ? 180 : 0))