SwiftUI view render performance Indicator

Measure.swift

//  Created by Baye Wayly on 2020/3/13.
//  Copyright © 2020 Baye. All rights reserved.

import SwiftUI

struct Measure<Content: View>: View {
  @State var cost: TimeInterval = 0
  var content: Content
  
  init(@ViewBuilder builder: () -> Content) {
    // discard first time
    content = builder()
    
    let start = Date()
    let count = 50
    for _ in 0..<count {
      content = builder()
    }
    self._cost = State(initialValue: Date().timeIntervalSince(start) / Double(count))
  }
  
  var body: some View {
    ZStack(alignment: .topLeading) {
      self.content
      Text("\(Int(self.cost * 1000_1000))μs")
        .font(.system(.caption, design: .monospaced))
        .padding(.vertical, 3)
        .padding(.horizontal, 5)
        .background(Color.orange)
        .foregroundColor(.white)
        .clipShape(RoundedRectangle(cornerRadius: 3))
    }
  }
}

struct Measure_Previews: PreviewProvider {
  static var previews: some View {
    Measure {
      Text("Hello World")
    }
  }
}

Preview.png

Hello