[译] SwiftUI 官方教程（六）

谁践踏了优雅 2022-10-01 08:51 234阅读 0赞

> **完整中文教程及代码请查看 [github.com/WillieWangW…][github.com_WillieWangW]**

# 动画 View 与转场 #

> 使用 `SwiftUI` 时，无论用作何处，我们都可以单独为 view 添加动画，或者对 view 的状态进行动画处理。 `SwiftUI` 为我们处理所有动画的组合、重叠和中断的复杂性。
> 
> 在本文中，我们会给包含图表的 view 设置动画，跟踪用户在使用 `Landmarks` app 时行为。我们会看到通过使用 `animation(_:)` 方法为 view 设置动画是多么简单。
> 
> 下载项目文件并按照以下步骤操作，也可以打开已完成的项目自行浏览代码。
> 
>  *  预计完成时间：20 分钟
>  *  项目文件：[下载][Link 1]

## 1. 给单个 View 添加动画 ##

当我们在一个 view 上使用 `animation(_:)` 方法时， `SwiftUI` 会动态的修改这个 view 的可动画属性。一个 view 的颜色、透明度、旋转、大小以及其他属性都是可动画的。

1.1 在 `HikeView.swift` 中，打开实时预览来测试显示和隐藏图表。

确保在本文中过程中都打开了实时预览，这样就可以测试到每一步的结果。

1.2 添加 `animation(.basic())` 方法来打开按钮的旋转动画。

> HikeView.swift

import SwiftUI
    
    struct HikeView: View {
        var hike: Hike
        @State private var showDetail = false
    
        var body: some View {
            VStack {
                HStack {
                    HikeGraph(data: hike.observations, path: \.elevation)
                        .frame(width: 50, height: 30)
    
                    VStack(alignment: .leading) {
                        Text(hike.name)
                            .font(.headline)
                        Text(hike.distanceText)
                    }
    
                    Spacer()
    
                    Button(action: {
                        self.showDetail.toggle()
                    }) {
                        Image(systemName: "chevron.right.circle")
                            .imageScale(.large)
                            .rotationEffect(.degrees(showDetail ? 90 : 0))
                            .padding()
                            .animation(.basic())
                    }
                }
    
                if showDetail {
                    HikeDetail(hike: hike)
                }
            }
        }
    }
    复制代码

1.3 添加一个在图表显示时让按钮变大的动画。

`animation(_:)` 会作用于 view 所包装的所有可动画的修改。

> HikeView.swift

import SwiftUI
    
    struct HikeView: View {
        var hike: Hike
        @State private var showDetail = false
    
        var body: some View {
            VStack {
                HStack {
                    HikeGraph(data: hike.observations, path: \.elevation)
                        .frame(width: 50, height: 30)
    
                    VStack(alignment: .leading) {
                        Text(hike.name)
                            .font(.headline)
                        Text(hike.distanceText)
                    }
    
                    Spacer()
    
                    Button(action: {
                        self.showDetail.toggle()
                    }) {
                        Image(systemName: "chevron.right.circle")
                            .imageScale(.large)
                            .rotationEffect(.degrees(showDetail ? 90 : 0))
                            .scaleEffect(showDetail ? 1.5 : 1)
                            .padding()
                            .animation(.basic())
                    }
                }
    
                if showDetail {
                    HikeDetail(hike: hike)
                }
            }
        }
    }
    复制代码

1.4 把动画类型从 `.basic()` 改成 `.spring()` 。

`SwiftUI` 包含带有预设或自定义缓动的基本动画，以及弹性和流体动画。我们可以调整动画的速度、在动画开始之前设置延迟，或指定动画的重复。

> HikeView.swift

import SwiftUI
    
    struct HikeView: View {
        var hike: Hike
        @State private var showDetail = false
    
        var body: some View {
            VStack {
                HStack {
                    HikeGraph(data: hike.observations, path: \.elevation)
                        .frame(width: 50, height: 30)
    
                    VStack(alignment: .leading) {
                        Text(hike.name)
                            .font(.headline)
                        Text(hike.distanceText)
                    }
    
                    Spacer()
    
                    Button(action: {
                        self.showDetail.toggle()
                    }) {
                        Image(systemName: "chevron.right.circle")
                            .imageScale(.large)
                            .rotationEffect(.degrees(showDetail ? 90 : 0))
                            .scaleEffect(showDetail ? 1.5 : 1)
                            .padding()
                            .animation(.spring())
                    }
                }
    
                if showDetail {
                    HikeDetail(hike: hike)
                }
            }
        }
    }
    复制代码

尝试在 `scaleEffect` 方法上方添加另一个动画方法来关闭旋转动画。

围绕 `SwiftUI` 尝试结合不同的动画效果，看看都有哪些效果。

> HikeView.swift

import SwiftUI
    
    struct HikeView: View {
        var hike: Hike
        @State private var showDetail = false
    
        var body: some View {
            VStack {
                HStack {
                    HikeGraph(data: hike.observations, path: \.elevation)
                        .frame(width: 50, height: 30)
    
                    VStack(alignment: .leading) {
                        Text(hike.name)
                            .font(.headline)
                        Text(hike.distanceText)
                    }
    
                    Spacer()
    
                    Button(action: {
                        self.showDetail.toggle()
                    }) {
                        Image(systemName: "chevron.right.circle")
                            .imageScale(.large)
                            .rotationEffect(.degrees(showDetail ? 90 : 0))
                            .animation(nil)
                            .scaleEffect(showDetail ? 1.5 : 1)
                            .padding()
                            .animation(.spring())
                    }
                }
    
                if showDetail {
                    HikeDetail(hike: hike)
                }
            }
        }
    }
    复制代码

1.6 在继续下一节前，删除两个 `animation(_:)` 方法。

> HikeView.swift

import SwiftUI
    
    struct HikeView: View {
        var hike: Hike
        @State private var showDetail = false
    
        var body: some View {
            VStack {
                HStack {
                    HikeGraph(data: hike.observations, path: \.elevation)
                        .frame(width: 50, height: 30)
    
                    VStack(alignment: .leading) {
                        Text(hike.name)
                            .font(.headline)
                        Text(hike.distanceText)
                    }
    
                    Spacer()
    
                    Button(action: {
                        self.showDetail.toggle()
                    }) {
                        Image(systemName: "chevron.right.circle")
                            .imageScale(.large)
                            .rotationEffect(.degrees(showDetail ? 90 : 0))
    
                            .scaleEffect(showDetail ? 1.5 : 1)
                            .padding()
    
                    }
                }
    
                if showDetail {
                    HikeDetail(hike: hike)
                }
            }
        }
    }
    复制代码

## 2. 将状态的改变动画化 ##

现在我们已经学会如果给单个 view 添加动画，是时候给状态的值的改变添加动画了。

这一节，我们会给用户点击按钮并切换 `showDetail` 状态属性时发生的所有更改添加动画。

2.1 将 `showDetail.toggle()` 的调用包装到 `withAnimation` 函数中。

受 `showDetail` 属性影响的公开按钮和 `HikeDetail` view 现在就都有了动画过渡。

> HikeView.swift

import SwiftUI
    
    struct HikeView: View {
        var hike: Hike
        @State private var showDetail = false
    
        var body: some View {
            VStack {
                HStack {
                    HikeGraph(data: hike.observations, path: \.elevation)
                        .frame(width: 50, height: 30)
    
                    VStack(alignment: .leading) {
                        Text(hike.name)
                            .font(.headline)
                        Text(hike.distanceText)
                    }
    
                    Spacer()
    
                    Button(action: {
                        withAnimation {
                            self.showDetail.toggle()
                        }
                    }) {
                        Image(systemName: "chevron.right.circle")
                            .imageScale(.large)
                            .rotationEffect(.degrees(showDetail ? 90 : 0))
                            .scaleEffect(showDetail ? 1.5 : 1)
                            .padding()
                    }
                }
    
                if showDetail {
                    HikeDetail(hike: hike)
                }
            }
        }
    }
    复制代码

减缓动画，看看 `SwiftUI` 动画是如何可以中断的。

2.2 给 `withAnimation` 方法传递一个 4 秒的基础动画。

我们可以传递相同类型的动画给 `animation(_:)` 的 `withAnimation` 函数。

> HikeView.swift

import SwiftUI
    
    struct HikeView: View {
        var hike: Hike
        @State private var showDetail = false
    
        var body: some View {
            VStack {
                HStack {
                    HikeGraph(data: hike.observations, path: \.elevation)
                        .frame(width: 50, height: 30)
    
                    VStack(alignment: .leading) {
                        Text(hike.name)
                            .font(.headline)
                        Text(hike.distanceText)
                    }
    
                    Spacer()
    
                    Button(action: {
                        withAnimation(.basic(duration: 4)) {
                            self.showDetail.toggle()
                        }
                    }) {
                        Image(systemName: "chevron.right.circle")
                            .imageScale(.large)
                            .rotationEffect(.degrees(showDetail ? 90 : 0))
                            .scaleEffect(showDetail ? 1.5 : 1)
                            .padding()
                    }
                }
    
                if showDetail {
                    HikeDetail(hike: hike)
                }
            }
        }
    }
    复制代码

2.3 尝试在动画期间打开和关闭图表 view 。

2.4 在进入下一节前，从 `withAnimation` 函数中移除缓慢动画。

> HikeView.swift

import SwiftUI
    
    struct HikeView: View {
        var hike: Hike
        @State private var showDetail = false
    
        var body: some View {
            VStack {
                HStack {
                    HikeGraph(data: hike.observations, path: \.elevation)
                        .frame(width: 50, height: 30)
    
                    VStack(alignment: .leading) {
                        Text(hike.name)
                            .font(.headline)
                        Text(hike.distanceText)
                    }
    
                    Spacer()
    
                    Button(action: {
                        withAnimation {
                            self.showDetail.toggle()
                        }
                    }) {
                        Image(systemName: "chevron.right.circle")
                            .imageScale(.large)
                            .rotationEffect(.degrees(showDetail ? 90 : 0))
                            .scaleEffect(showDetail ? 1.5 : 1)
                            .padding()
                    }
                }
    
                if showDetail {
                    HikeDetail(hike: hike)
                }
            }
        }
    }
    复制代码

## 3. 自定义 View 的转场 ##

默认情况下，view 通过淡入和淡出过渡到屏幕上和屏幕外。我们可以使用 `transition(_:)` 方法来自定义转场。

3.1 给满足条件时显示的 `HikeView` 添加一个 `transition(_:)` 方法。

现在图标会滑动显示和消失。

> HikeView.swift

import SwiftUI
    
    struct HikeView: View {
        var hike: Hike
        @State private var showDetail = false
    
        var body: some View {
            VStack {
                HStack {
                    HikeGraph(data: hike.observations, path: \.elevation)
                        .frame(width: 50, height: 30)
    
                    VStack(alignment: .leading) {
                        Text(hike.name)
                            .font(.headline)
                        Text(hike.distanceText)
                    }
    
                    Spacer()
    
                    Button(action: {
                        withAnimation {
                            self.showDetail.toggle()
                        }
                    }) {
                        Image(systemName: "chevron.right.circle")
                            .imageScale(.large)
                            .rotationEffect(.degrees(showDetail ? 90 : 0))
                            .scaleEffect(showDetail ? 1.5 : 1)
                            .padding()
                    }
                }
    
                if showDetail {
                    HikeDetail(hike: hike)
                        .transition(.slide)
                }
            }
        }
    }
    复制代码

3.2 将转场提取为 `AnyTransition` 的静态属性。

这可以在您展开自定义转场时保持代码清晰。对于自定义转场，我们可以使用与 `SwiftUI` 所用相同的 `.` 符号。

> HikeView.swift

import SwiftUI
    
    extension AnyTransition {
        static var moveAndFade: AnyTransition {
            AnyTransition.slide
        }
    }
    
    struct HikeView: View {
        var hike: Hike
        @State private var showDetail = false
    
        var body: some View {
            VStack {
                HStack {
                    HikeGraph(data: hike.observations, path: \.elevation)
                        .frame(width: 50, height: 30)
    
                    VStack(alignment: .leading) {
                        Text(hike.name)
                            .font(.headline)
                        Text(hike.distanceText)
                    }
    
                    Spacer()
    
                    Button(action: {
                        withAnimation {
                            self.showDetail.toggle()
                        }
                    }) {
                        Image(systemName: "chevron.right.circle")
                            .imageScale(.large)
                            .rotationEffect(.degrees(showDetail ? 90 : 0))
                            .scaleEffect(showDetail ? 1.5 : 1)
                            .padding()
                    }
                }
    
                if showDetail {
                    HikeDetail(hike: hike)
                        .transition(.moveAndFade)
                }
            }
        }
    }
    复制代码

3.3 换成使用 `move(edge:)` 转场，这样图表会从同一边滑入和滑出。

> HikeView.swift

import SwiftUI
    
    extension AnyTransition {
        static var moveAndFade: AnyTransition {
            AnyTransition.move(edge: .trailing)
        }
    }
    
    struct HikeView: View {
        var hike: Hike
        @State private var showDetail = false
    
        var body: some View {
            VStack {
                HStack {
                    HikeGraph(data: hike.observations, path: \.elevation)
                        .frame(width: 50, height: 30)
    
                    VStack(alignment: .leading) {
                        Text(hike.name)
                            .font(.headline)
                        Text(hike.distanceText)
                    }
    
                    Spacer()
    
                    Button(action: {
                        withAnimation {
                            self.showDetail.toggle()
                        }
                    }) {
                        Image(systemName: "chevron.right.circle")
                            .imageScale(.large)
                            .rotationEffect(.degrees(showDetail ? 90 : 0))
                            .scaleEffect(showDetail ? 1.5 : 1)
                            .padding()
                    }
                }
    
                if showDetail {
                    HikeDetail(hike: hike)
                        .transition(.moveAndFade)
                }
            }
        }
    }
    复制代码

3.4 使用 `asymmetric(insertion:removal:)` 方法来给 view 显示和消失时提供不同的转场。

> HikeView.swift

import SwiftUI
    
    extension AnyTransition {
        static var moveAndFade: AnyTransition {
            let insertion = AnyTransition.move(edge: .trailing)
                .combined(with: .opacity)
            let removal = AnyTransition.scale()
                .combined(with: .opacity)
            return .asymmetric(insertion: insertion, removal: removal)
        }
    }
    
    struct HikeView: View {
        var hike: Hike
        @State private var showDetail = false
    
        var body: some View {
            VStack {
                HStack {
                    HikeGraph(data: hike.observations, path: \.elevation)
                        .frame(width: 50, height: 30)
    
                    VStack(alignment: .leading) {
                        Text(hike.name)
                            .font(.headline)
                        Text(hike.distanceText)
                    }
    
                    Spacer()
    
                    Button(action: {
                        withAnimation {
                            self.showDetail.toggle()
                        }
                    }) {
                        Image(systemName: "chevron.right.circle")
                            .imageScale(.large)
                            .rotationEffect(.degrees(showDetail ? 90 : 0))
                            .scaleEffect(showDetail ? 1.5 : 1)
                            .padding()
                    }
                }
    
                if showDetail {
                    HikeDetail(hike: hike)
                        .transition(.moveAndFade)
                }
            }
        }
    }
    复制代码

## 4. 给复杂的效果组合动画 ##

单击条形下方的按钮时，图形会在三组不同的数据之间切换。在本节中，我们将使用组合动画为构成图形的 `Capsule` 提供动态、波动的转场。

4.1 把 `showDetail` 的默认值改成 `true` ，并把 `HikeView` 的预览固定在 `canvas` 中，

这让我们在其他文件中制作动画时依然能在上下文中看到图表。

4.2 在 `GraphCapsule.swift` 中，添加一个新的计算动画属性，并将其应用于 `Capsule` 的 `shape` 。

> GraphCapsule.swift

import SwiftUI
    
    struct GraphCapsule: View {
        var index: Int
        var height: Length
        var range: Range<Double>
        var overallRange: Range<Double>
    
        var heightRatio: Length {
            max(Length(magnitude(of: range) / magnitude(of: overallRange)), 0.15)
        }
    
        var offsetRatio: Length {
            Length((range.lowerBound - overallRange.lowerBound) / magnitude(of: overallRange))
        }
    
        var animation: Animation {
            Animation.default
        }
    
        var body: some View {
            Capsule()
                .fill(Color.gray)
                .frame(height: height * heightRatio, alignment: .bottom)
                .offset(x: 0, y: height * -offsetRatio)
                .animation(animation)
            )
        }
    }
    复制代码

4.3 将动画改为弹性动画，使用初始速度让条形图跳跃。

> GraphCapsule.swift

import SwiftUI
    
    struct GraphCapsule: View {
        var index: Int
        var height: Length
        var range: Range<Double>
        var overallRange: Range<Double>
    
        var heightRatio: Length {
            max(Length(magnitude(of: range) / magnitude(of: overallRange)), 0.15)
        }
    
        var offsetRatio: Length {
            Length((range.lowerBound - overallRange.lowerBound) / magnitude(of: overallRange))
        }
    
        var animation: Animation {
            Animation.spring(initialVelocity: 5)
        }
    
        var body: some View {
            Capsule()
                .fill(Color.gray)
                .frame(height: height * heightRatio, alignment: .bottom)
                .offset(x: 0, y: height * -offsetRatio)
                .animation(animation)
            )
        }
    }
    复制代码

4.4 加快动画速度，缩短每个小节移动到新位置所需的时间。

> GraphCapsule.swift

import SwiftUI
    
    struct GraphCapsule: View {
        var index: Int
        var height: Length
        var range: Range<Double>
        var overallRange: Range<Double>
    
        var heightRatio: Length {
            max(Length(magnitude(of: range) / magnitude(of: overallRange)), 0.15)
        }
    
        var offsetRatio: Length {
            Length((range.lowerBound - overallRange.lowerBound) / magnitude(of: overallRange))
        }
    
        var animation: Animation {
            Animation.spring(initialVelocity: 5)
                .speed(2)
        }
    
        var body: some View {
            Capsule()
                .fill(Color.gray)
                .frame(height: height * heightRatio, alignment: .bottom)
                .offset(x: 0, y: height * -offsetRatio)
                .animation(animation)
            )
        }
    }
    复制代码

4.5 根据 `Capsule` 在图表上的位置为每个动画添加延迟。

> GraphCapsule.swift

import SwiftUI
    
    struct GraphCapsule: View {
        var index: Int
        var height: Length
        var range: Range<Double>
        var overallRange: Range<Double>
    
        var heightRatio: Length {
            max(Length(magnitude(of: range) / magnitude(of: overallRange)), 0.15)
        }
    
        var offsetRatio: Length {
            Length((range.lowerBound - overallRange.lowerBound) / magnitude(of: overallRange))
        }
    
        var animation: Animation {
            Animation.spring(initialVelocity: 5)
                .speed(2)
                .delay(0.03 * Double(index))
        }
    
        var body: some View {
            Capsule()
                .fill(Color.gray)
                .frame(height: height * heightRatio, alignment: .bottom)
                .offset(x: 0, y: height * -offsetRatio)
                .animation(animation)
            )
        }
    }
    复制代码

4.6 观察自定义动画在图表之间转场时是如何营造波纹效果的。

转载于:https://juejin.im/post/5cfbc5356fb9a07ee1691b10

[github.com_WillieWangW]: https://link.juejin.im?target=https%3A%2F%2Fgithub.com%2FWillieWangWei%2FSwiftUI-Tutorials
[Link 1]: https://link.juejin.im?target=https%3A%2F%2Fdocs-assets.developer.apple.com%2Fpublished%2F21618cac9f%2FAnimatingViewsAndTransitions.zip