Notes for SwiftUI and Combine Programming (1)

I start reading onevcat new book SwiftUI and Combine Programming (a great book to learning SwiftUI if you can read Chinese). I decided to put all the interest parts and notes in here.

First things First

We always need to import the dependency first

import SwiftUI
import Combine

Layout all the views in the body

var body: some View {
    /// Layout your view here
}

some View is a new concept introduced in Swift 5.1, which called Opaque Types. Maybe someday I will write a more detail post for opaque types, in short, opaque types kind like protocol but more powerful.

Enable Canvas in Xcode

You can preview the UI layouts using Canvas, which is convincing by PreviewProvider. As long as your swift file have a struct confirm it, you will able to work with SwiftUI and preview changes using Canvas support (Xcode 11+ and OS X 10.15 + Only)

struct MyView_Previews: PreviewProvider {
    static var previews: some View {
        MyView()
    }
}

Canvas is not fast

At least not fast as I wish, we still need to build the whole project first, then it starts working as we hope. But sometimes I found I may easier break the UI, then Xcode start not happy anymore, showing this on canvas

In this case, we have to resume the canvas which rebuilds the project again 😢

Preview with multiple devices

Canvas support preview with all devices, so we can work on different size of screens:

struct ContentView_Previews : PreviewProvider {
    static var previews: some View {
        Group {
            ContentView()
            ContentView().previewDevice("iPhone SE")
            ContentView().previewDevice("iPad Air 2")
        }
    }
}

After some loading 😫, we should see something like this: