Created
July 13, 2020 11:24
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| // | |
| // ContentView.swift | |
| // AnchorPreferencesDemo | |
| // | |
| // Created by MC on 2020/7/13. | |
| // | |
| import SwiftUI | |
| struct ContentView: View { | |
| var body: some View { | |
| Example1() | |
| } | |
| } | |
| struct Example1: View { | |
| @State private var titles = ["推荐", "要闻", "视频", "抗疫", "北京", | |
| "新时代", "娱乐", "体育", "军事", "NBA", | |
| "科技", "财经", "时尚"] | |
| @State private var selectedIndex: Int = 0 | |
| var body: some View { | |
| ScrollView(.horizontal, showsIndicators: false) { | |
| HStack(spacing: 0) { | |
| ForEach(0..<titles.count) { index in | |
| SegementItem(title: titles[index], | |
| index: index, | |
| selectedIndex: selectedIndex) | |
| .onTapGesture { | |
| withAnimation { | |
| self.selectedIndex = index | |
| } | |
| } | |
| } | |
| } | |
| } | |
| .backgroundPreferenceValue(MySegementPreferenceKey.self) { preferences in | |
| GeometryReader { proxy in | |
| self.createBottomLine(proxy, preferences: preferences) | |
| } | |
| } | |
| } | |
| struct SegementItem: View { | |
| let title: String | |
| let index: Int | |
| let selectedIndex: Int | |
| var body: some View { | |
| Text(title) | |
| .scaleEffect(index == self.selectedIndex ? 1.5 : 1.0) | |
| .font(.title) | |
| .foregroundColor(index == self.selectedIndex ? .primary : .secondary) | |
| .padding(.all, /*@START_MENU_TOKEN@*/10/*@END_MENU_TOKEN@*/) | |
| .anchorPreference(key: MySegementPreferenceKey.self, value: .bounds, transform: { | |
| [MySegementPreferenceData(viewIdx: index, bounds: $0)] | |
| }) | |
| .transformAnchorPreference(key: MySegementPreferenceKey.self, value: .topLeading, transform: { (value: inout [MySegementPreferenceData], anchor: Anchor<CGPoint>) in | |
| value[0].topLeading = anchor | |
| }) | |
| } | |
| } | |
| func createBottomLine(_ proxy: GeometryProxy, preferences: [MySegementPreferenceData]) -> some View { | |
| let p = preferences.first(where: { $0.viewIdx == self.selectedIndex }) | |
| let bounds = proxy[p!.bounds] | |
| return RoundedRectangle(cornerRadius: 2.5) | |
| .foregroundColor(.green) | |
| .frame(width: bounds.width, height: 5) | |
| .offset(x: bounds.minX, y: bounds.height - 5) | |
| // .animation(.easeInOut) | |
| } | |
| } | |
| struct MySegementPreferenceData { | |
| let viewIdx: Int | |
| let bounds: Anchor<CGRect> | |
| var topLeading: Anchor<CGPoint>? = nil | |
| } | |
| struct MySegementPreferenceKey: PreferenceKey { | |
| typealias Value = [MySegementPreferenceData] | |
| static var defaultValue: Value = [] | |
| static func reduce(value: inout [MySegementPreferenceData], nextValue: () -> [MySegementPreferenceData]) { | |
| value.append(contentsOf: nextValue()) | |
| } | |
| } | |
| struct ContentView_Previews: PreviewProvider { | |
| static var previews: some View { | |
| ContentView() | |
| } | |
| } |
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