###### tags: `第14屆IT邦鐵人賽文章`

# 【在 iOS 開發路上的大小事2－Day25】來自 Apple 爸爸的最新力作 - Swift Charts 之 LineMark 實作篇

上一篇介紹了 AreaMark 的實作，今天要來介紹的是 Swift Charts 的 LineMark

LineMark 一共提供了兩種 init 的方法，讓開發者可以繪製不同樣式的圖表

public init<X, Y>(x: PlottableValue<X>, 
                  y: PlottableValue<Y>) where X : Plottable, Y : Plottable

public init<X, Y, S>(x: PlottableValue<X>, 
                     y: PlottableValue<Y>, 
                     series: PlottableValue<S>) where X : Plottable, Y : Plottable, S : Plottable

我們就以護國神山台積電跟友達的股票收盤價來當作範例

## Model

import SwiftUI

struct StockEntity: Identifiable {
    
    var id = UUID().uuidString
    
    let name: String // 公司名稱
    
    let highestPrice: Double // 當日最高點
    
    let lowestPrice: Double // 當日最低點
    
    let endPrice: Double // 當日收盤價
    
    let date: Date // 日期
    
    init(name: String, highestPrice: Double, lowestPrice: Double, endPrice: Double, month: Int, day: Int) {
        self.name = name
        self.highestPrice = highestPrice
        self.lowestPrice = lowestPrice
        self.endPrice = endPrice
        let calender = Calendar.autoupdatingCurrent
        self.date = calender.date(from: DateComponents(month: month, day: day))!
    }
}

## ViewModel

import SwiftUI

class StockEntityViewModel {

    var stockData: [StockEntity] = [
        
        // MARK: TSMC Stock Price
        .init(name: "TSMC", highestPrice: 523.00, lowestPrice: 517.00, endPrice: 519.00, month: 8, day: 19),
        .init(name: "TSMC", highestPrice: 514.00, lowestPrice: 510.00, endPrice: 510.00, month: 8, day: 22),
        .init(name: "TSMC", highestPrice: 506.00, lowestPrice: 502.00, endPrice: 504.00, month: 8, day: 23),
        .init(name: "TSMC", highestPrice: 508.00, lowestPrice: 503.00, endPrice: 503.00, month: 8, day: 24),
        .init(name: "TSMC", highestPrice: 510.00, lowestPrice: 504.00, endPrice: 508.00, month: 8, day: 25),
        .init(name: "TSMC", highestPrice: 515.00, lowestPrice: 511.00, endPrice: 512.00, month: 8, day: 26),
        .init(name: "TSMC", highestPrice: 502.00, lowestPrice: 496.00, endPrice: 498.50, month: 8, day: 29),
        .init(name: "TSMC", highestPrice: 500.00, lowestPrice: 496.00, endPrice: 496.00, month: 8, day: 30),
        .init(name: "TSMC", highestPrice: 505.00, lowestPrice: 492.00, endPrice: 505.00, month: 8, day: 31),
        .init(name: "TSMC", highestPrice: 495.50, lowestPrice: 490.00, endPrice: 490.50, month: 9, day: 1),
        .init(name: "TSMC", highestPrice: 489.50, lowestPrice: 485.00, endPrice: 485.00, month: 9, day: 2),
        .init(name: "TSMC", highestPrice: 488.00, lowestPrice: 484.00, endPrice: 486.00, month: 9, day: 5),
        .init(name: "TSMC", highestPrice: 491.50, lowestPrice: 486.50, endPrice: 489.00, month: 9, day: 6),
        .init(name: "TSMC", highestPrice: 478.00, lowestPrice: 472.00, endPrice: 472.50, month: 9, day: 7),
        .init(name: "TSMC", highestPrice: 475.00, lowestPrice: 472.00, endPrice: 475.00, month: 9, day: 8),
        
        // MARK: AUO Stock Price
        .init(name: "AUO", highestPrice: 17.15, lowestPrice: 15.70, endPrice: 16.95, month: 8, day: 19),
        .init(name: "AUO", highestPrice: 16.95, lowestPrice: 16.60, endPrice: 16.95, month: 8, day: 22),
        .init(name: "AUO", highestPrice: 16.80, lowestPrice: 15.75, endPrice: 16.00, month: 8, day: 23),
        .init(name: "AUO", highestPrice: 16.40, lowestPrice: 16.05, endPrice: 16.15, month: 8, day: 24),
        .init(name: "AUO", highestPrice: 16.30, lowestPrice: 15.95, endPrice: 16.10, month: 8, day: 25),
        .init(name: "AUO", highestPrice: 16.25, lowestPrice: 16.00, endPrice: 16.15, month: 8, day: 26),
        .init(name: "AUO", highestPrice: 16.05, lowestPrice: 15.40, endPrice: 15.75, month: 8, day: 29),
        .init(name: "AUO", highestPrice: 16.70, lowestPrice: 16.15, endPrice: 16.40, month: 8, day: 30),
        .init(name: "AUO", highestPrice: 16.75, lowestPrice: 16.15, endPrice: 16.75, month: 8, day: 31),
        .init(name: "AUO", highestPrice: 17.25, lowestPrice: 16.45, endPrice: 17.10, month: 9, day: 1),
        .init(name: "AUO", highestPrice: 17.35, lowestPrice: 16.70, endPrice: 16.90, month: 9, day: 2),
        .init(name: "AUO", highestPrice: 17.45, lowestPrice: 16.80, endPrice: 17.40, month: 9, day: 5),
        .init(name: "AUO", highestPrice: 17.70, lowestPrice: 17.25, endPrice: 17.50, month: 9, day: 6),
        .init(name: "AUO", highestPrice: 17.60, lowestPrice: 17.10, endPrice: 17.40, month: 9, day: 7),
        .init(name: "AUO", highestPrice: 17.60, lowestPrice: 17.30, endPrice: 17.35, month: 9, day: 8),
    ]
}

## View

這邊要記得 ```import Charts```，因為我們要顯示 LineMark 在畫面上

然後這邊宣告了一個 ViewModel 的變數 vm
並在前面加上 ```@State``` 修飾字，讓 SwiftUI 來幫我們管理 ViewModel 狀態

接著是 Charts 的語法，語法也是很簡單，像是下面這樣

@State private var vm = StockEntityViewModel()

// 1：vm.stockData，圖表的資料來源
Chart(vm.stockData) {
    LineMark(
        x: .value("Date", $0.date), // 2：x 軸要顯示的資料
        y: .value("End Price", $0.endPrice) // 3：y 軸要顯示的資料
    )
    .foregroundStyle(by: .value("Stock Name", $0.name)) // 4：左下角的圖例樣式 or 圖表的外觀樣式
}

或者你也可以透過 ForEach 來寫，只是就會要讓 Model 繼承 ```Identifiable```
並宣告 UUID() 變數在 Model 裡面，像是這樣 ```var id = UUID().uuidString```

@State private var vm = StockEntityViewModel()

Chart {
    // 1：vm.stockData，圖表的資料來源
    ForEach(vm.stockData) { data in
        LineMark(
            x: .value("Date", data.date), // 2：x 軸要顯示的資料
            y: .value("End Price", data.endPrice) // 3：y 軸要顯示的資料
        )
        .foregroundStyle(by: .value("Stock Name", data.name)) // 4：左下角的圖例樣式 or 圖表的外觀樣式
    }
}

## 來幫每筆資料加上圖案吧

現在的圖應該會長得像是下面這樣


但這樣看起來，感覺有點單調，來幫每筆資料加上圖案好了

加圖案的語法也很簡單，像是下面這樣

@State private var vm = StockEntityViewModel()

Chart {
    ForEach(vm.stockData) { data in
        LineMark(
            x: .value("Date", data.date),
            y: .value("End Price", data.endPrice)
        )
        .foregroundStyle(by: .value("Stock Name", data.name))
        .symbol(.square) // 圖案類型
        .symbolSize(100) // 圖案大小
    }
}

加完以後，現在會長的像是這樣


那總共有哪些圖案呢？讓我們來一起看一下～

@available(iOS 16.0, macOS 13.0, tvOS 16.0, watchOS 9.0, *)
extension ChartSymbolShape where Self == BasicChartSymbolShape {

    /// 圓形樣式
    public static var circle: BasicChartSymbolShape { get }

    /// 矩形樣式
    public static var square: BasicChartSymbolShape { get }

    /// 三角形樣式
    public static var triangle: BasicChartSymbolShape { get }

    /// 菱形樣式
    public static var diamond: BasicChartSymbolShape { get }

    /// 五邊形樣式
    public static var pentagon: BasicChartSymbolShape { get }

    /// 加號樣式
    public static var plus: BasicChartSymbolShape { get }

    /// 十字樣式
    public static var cross: BasicChartSymbolShape { get }

    /// 雪花樣式
    public static var asterisk: BasicChartSymbolShape { get }
}

## 讓圖案樣式可以自由選擇

### 基本版

首先我們先宣告一個 symbol 變數，以及建立一個 Menu

@State private var symbol: BasicChartSymbolShape = .square

Menu {
    
} label: {
    
}

然後在 ```label:``` 這個 Closure 裡面顯示一個 ```Text```，用來當作提示使用者的文字，像是下面這樣

Menu {
    
} label: {
    Text("Choose Symbol")   
}

接著，我們要來製作 Menu 裡面要顯示的選項，製作之前，先來看一下 Apple 是怎麼定義 Menu 的


在 content 這個 Closure 裡面要放的是 Menu 的選項，而選項都是透過 Button 來宣告的

所以如果要建立所有圖案樣式的 Menu 的話，可以像下面這樣寫

Menu {
    Button {
        symbol = .square
    } label: {
        Label("Square", systemImage: "square")
    }
    Button {
        symbol = .circle
    } label: {
        Label("Circle", systemImage: "circle")
    }
    Button {
        symbol = .triangle
    } label: {
        Label("Triangle", systemImage: "triangle")
    }
    Button {
        symbol = .diamond
    } label: {
        Label("Diamond", systemImage: "diamond")
    }
    Button {
        symbol = .pentagon
    } label: {
        Label("Pentagon", systemImage: "pentagon")
    }
    Button {
        symbol = .plus
    } label: {
        Label("Plus", systemImage: "plus")
    }
    Button {
        symbol = .cross
    } label: {
        Label("Cross", systemImage: "cross")
    }
    Button {
        symbol = .asterisk
    } label: {
        Label("Asterisk", systemImage: "asterisk")
    }
} label: {
    Text("Choose Symbol")
}

現在畫面上看起來會長的像這樣


### 優化版

但這樣看起來，Code 實在太醜了，讓我們來做點修改吧

首先先建立一個叫做 MenuSymbolButton 的 SwiftUI View，像是下面這樣

struct MenuSymbolButton: View {
    
    var body: some View {

    }
}

然後在 body 裡面，宣告一個 Button 元件，像是下面這樣

struct MenuSymbolButton: View {
    
    var body: some View {
        Button {

        } label: {
            
        }
    }
}

接著在宣告要用來顯示每個圖案選項的 圖案文字 跟 圖案的圖片名稱 的變數

var symbolName: String // 圖案文字

var symbolImageName: String // 圖案的圖片名稱

接下來是最重要的一步，將連結兩個 View 之間的橋樑就在這裡了

宣告一個 ```@Binding``` 的 symbol 變數，用來跟另外一個 View 裡面的 ```@State``` symbol 變數進行綁定

@Binding var symbol: BasicChartSymbolShape

到這邊 MenuSymbolButton 所需的變數都宣告好了，就讓我們組合起來吧
現在的 MenuSymbolButton 應該會長得像下面這樣

struct MenuSymbolButton: View {
   
    @Binding var symbol: BasicChartSymbolShape
    
    var symbolName: String
    
    var symbolImageName: String
    
    var body: some View {
        Button {

        } label: {

        }
    }
}

我們先來組合 ```label:``` 裡面要顯示的內容

Button {

} label: {
    Label(symbolName, systemImage: symbolImageName)
}

接著再組合 ```action:``` 裡面要做的事情

這裡是透過 symbolImageName 來進行 switch

Button {
    symbol = {
        switch symbolImageName {
        case "square": return .square
        case "circle": return .circle
        case "triangle": return .triangle
        case "diamond": return .diamond
        case "pentagon": return .pentagon
        case "plus": return .plus
        case "cross": return .cross
        case "asterisk": return .asterisk
        default: return .square
        }
    }()
} label: {
    Label(symbolName, systemImage: symbolImageName)
}

### 將原本的 Menu 改寫

剛才將 MenuSymbolButton 設計好了，就要來將原本的一長串 Button 進行改寫了～

改寫完，就長的像是下面這樣

Menu {
    MenuSymbolButton(symbol: $symbol, symbolName: "Square", symbolImageName: "square")
    MenuSymbolButton(symbol: $symbol, symbolName: "Circle", symbolImageName: "circle")
    MenuSymbolButton(symbol: $symbol, symbolName: "Triangle", symbolImageName: "triangle")
    MenuSymbolButton(symbol: $symbol, symbolName: "Diamond", symbolImageName: "diamond")
    MenuSymbolButton(symbol: $symbol, symbolName: "Pentagon", symbolImageName: "pentagon")
    MenuSymbolButton(symbol: $symbol, symbolName: "Plus", symbolImageName: "plus")
    MenuSymbolButton(symbol: $symbol, symbolName: "Cross", symbolImageName: "cross")
    MenuSymbolButton(symbol: $symbol, symbolName: "Asterisk", symbolImageName: "asterisk")
} label: {
    Text("Choose Symbol")
}

### 將 Charts 的 symbol 修飾字改寫

到這邊，就只剩下最後一步要做了

現在 Charts 的 symbol 還是透過直接給值的方式，來做設定

現在就要來將這邊做改寫！改寫完會長的像下面這樣

@State private var vm = StockEntityViewModel()

Chart {
    ForEach(vm.stockData) { data in
        LineMark(
            x: .value("Date", data.date),
            y: .value("End Price", data.endPrice)
        )
        .foregroundStyle(by: .value("Stock Name", data.name))
        .symbol(symbol) // 原本是直接給 .square，現在改成給 symbol 變數，讓 SwiftUI 自動更新變數狀態
        .symbolSize(100)
    }
}

## 完整程式碼

import SwiftUI
import Charts

struct LineMarkView: View {
    
    @State private var symbol: BasicChartSymbolShape = .square
    
    @State private var vm = StockEntityViewModel()
    
    var body: some View {
        VStack {
            Chart {
                ForEach(vm.stockData) { data in
                    LineMark(
                        x: .value("Date", data.date),
                        y: .value("End Price", data.endPrice)
                    )
                    .foregroundStyle(by: .value("Stock Name", data.name))
                    .symbol(symbol)
                    .symbolSize(100)
                }
            }
            .chartXAxisLabel("Date (2022/8/19~2022/9/8)", alignment: .leading)
            .chartYAxisLabel("Price (NTD)", alignment: .trailing)
            .frame(height: 300)
            .padding()
            
            Menu {
                MenuSymbolButton(symbol: $symbol, symbolName: "Square", symbolImageName: "square")
                MenuSymbolButton(symbol: $symbol, symbolName: "Circle", symbolImageName: "circle")
                MenuSymbolButton(symbol: $symbol, symbolName: "Triangle", symbolImageName: "triangle")
                MenuSymbolButton(symbol: $symbol, symbolName: "Diamond", symbolImageName: "diamond")
                MenuSymbolButton(symbol: $symbol, symbolName: "Pentagon", symbolImageName: "pentagon")
                MenuSymbolButton(symbol: $symbol, symbolName: "Plus", symbolImageName: "plus")
                MenuSymbolButton(symbol: $symbol, symbolName: "Cross", symbolImageName: "cross")
                MenuSymbolButton(symbol: $symbol, symbolName: "Asterisk", symbolImageName: "asterisk")
            } label: {
                Text("Choose Symbol")
            }

        }
    }
}

struct LineMarkView_Previews: PreviewProvider {
    static var previews: some View {
        LineMarkView()
    }
}

struct MenuSymbolButton: View {
   
    @Binding var symbol: BasicChartSymbolShape
    
    var symbolName: String
    
    var symbolImageName: String
    
    var body: some View {
        Button {
            symbol = {
                switch symbolImageName {
                case "square": return .square
                case "circle": return .circle
                case "triangle": return .triangle
                case "diamond": return .diamond
                case "pentagon": return .pentagon
                case "plus": return .plus
                case "cross": return .cross
                case "asterisk": return .asterisk
                default: return .square
                }
            }()
        } label: {
            Label(symbolName, systemImage: symbolImageName)
        }
    }
}

## 總結

這篇簡單實作了 Swift Charts 中的 LineMark

明天會來介紹 Swift Charts 中的 PointMark，讓我們繼續看下去吧～

## 參考資料

> 1. [https://developer.apple.com/documentation/charts/areamark](https://developer.apple.com/documentation/charts/linemark)