Swift for Good: Volume One by Paul Hudson

Author:Paul Hudson
Language: eng
Format: epub

When we combine those things, some important behavior emerges: it’s almost free to pull some code out of a SwiftUI view and place it into a new view of its own. Yes, there is a small cost because SwiftUI still needs to collapse our view hierarchy before it can be rendered, but that cost is minuscule – so low you won’t even notice it even if you aggressively break out your views. Apple even provides us with a simple recommendation to drive the point home: “you should never hesitate to refactor your SwiftUI code because extracting a subview has virtually no runtime overhead.”

In our ContentView code we have all the work to lay out a single row mixed in with the code to present the list and a navigation view. The job of ContentView really ought to be limited to showing a list of users, not to decide how each row should present itself – by putting all that code in one place we now can’t use it elsewhere, we can’t easily switch layouts in ContentView, and we’re also making the code harder to read.

So, your first logical step is to extract that part of the view hierarchy into a new view like this one:

struct SummaryView: View { let item: User var body: some View { NavigationLink(destination: DetailView(item: item)) { Image(item.id) .resizable() .frame(width: 44, height: 44) .clipShape(RoundedRectangle(cornerRadius: 10)) .overlay(RoundedRectangle(cornerRadius: 10).stroke(Color.black, lineWidth: 1)) VStack(alignment: .leading) { Text(item.name) .font(.system(.headline, design: .rounded)) Text(item.job) .font(.system(.body, design: .rounded)) .foregroundColor(.secondary) } } } }

And now ContentView becomes trivial:

NavigationView { List(users, rowContent: SummaryView.init) }

This is a great step forward: ContentView now focuses on navigation, so you can add a title and bar button items, while SummaryView focuses on what it means to display one piece of data.

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