You can develop apps to iOS, watchOS, etc. but inside them you have templates that are just starting points for certain type of apps.

Language: Swift

User Interface: SwiftUI (Storyboard is the same as UIKit)

• SwiftUI is a new thing and most of the old tutorials talk about UIKit

ContentView.swift

• By pressing resume you can see what the code looks like in a device. This updates automatically when the code is changed.
• ContectView_Previews is not something that's changed often and can be "hide" by adding a lot of line breaks. It just shows the View in the preview and can be deleted without getting any errors.

• SwiftUI is imported every time there is something happening in the UI and foundation is imported when we do something else because it contains things like arrays, dictionaries, etc.

• struct in Swift is more powerful than in some other languages because instead of just storing variables it can contain functions and behaviors.

• struct ContectView: View means that ContectView behaves/functions like View

• ContentView is the whole app background area of the device.

• var (variable) inside struct is called property.

• var body: some View where some View is type.

  • some keyword means that it can be any type as long as it behaves like View

• View returns one view but ViewContainer returns multiple.

• One line function doesn't need return keyword.

• some View could be Text in this example

  • some View is better format because then compiler makes the decision and often the return type changes which would also require changing this if not using some View

• It's normal to use labels when giving parameters to functions

  • return RoudedRectangle(cornerRadius: 10.0)

struct ContentView: View {
  var body: some View {
    return ZStack(content: {
      RoundedRectangle(cornerRadius: 10.0).stroke().foregroundColor(Color.orange)
      Text("ghost")
    })
  }
}

• Some people put .something (called View Function) to new line to stand out from other code more easily

struct ContentView: View {
  var body: some View {
    return ForEach(0..<4, content: { index in  
      ZStack(content: {
        RoundedRectangle(cornerRadius: 10.0).fill(Color.white)
        RoundedRectangle(cornerRadius: 10.0).stroke(lineWidth: 3)
        Text("ghost")
      })
    })
        .padding()
        .foregroundColor(Color.orange)
        .font(Font.largeTitle)
  }
}

• 0..<4 is same as [0,1,2,3]
• Two RoundedRectangle because the other is border and other is the background.

• ForEach is not Layout View the same way ZStack and that is why it should be inside a Layout View.

• If the last argument of a function is curly brace function it can be written abc(first: 1) {stuff} after the function call.

  • If no other arguments () can be removed too.

@RealLankinen

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Originally published here