Ios SwiftUI图表默认情况下，X轴数据点的间距不相等

与其使用Date，不如创建自己的Plottable类型，它的行为类似于String(即primitivePlottable返回String).SwiftData将字符串视为分类数据，并以相等的间距绘制它们.

struct YearMonthDay: Plottable, Hashable {
    init(year: Int, month: Int, day: Int) {
        self.year = year
        self.month = month
        self.day = day
    }
    
    init?(primitivePlottable: String) {
        guard let date = try? Date.ISO8601FormatStyle.iso8601.parse(primitivePlottable) else {
            return nil
        }
        let components = Calendar.current.dateComponents([.year, .month, .day], from: date)
        guard let day = components.day, let month = components.month, let year = components.year else {
            return nil
        }
        self.day = day
        self.month = month
        self.year = year
    }
    
    let year: Int
    let month: Int
    let day: Int
    
    var primitivePlottable: String {
        date.formatted(.iso8601)
    }
    
    // this will be useful later
    var date: Date {
        Calendar.current.date(from: DateComponents(year: year, month: month, day: day))!
    }
}

然后，DummySession struct 将声明为:

struct Session: Identifiable {
    let date: YearMonthDay
    let profit: Int
    
    var id: YearMonthDay {
        date
    }
}

创建图表时，应按所需格式设置X轴标签的格式:

Chart {
    ForEach(data) { session in
        LineMark(x: .value("Date", session.date),
                 y: .value("Profit", session.profit))
        .lineStyle(.init(lineWidth: 3, lineCap: .round, lineJoin: .round))
    }
    .interpolationMethod(.cardinal)
}
.chartXAxis {
    AxisMarks { value in
        if let yearMonthDay = value.as(YearMonthDay.self) {
            AxisValueLabel {
                Text(yearMonthDay.date, format: .dateTime.month().day())
            }
        }
    }
}
.chartYAxis {
    AxisMarks(position: .trailing, values: .automatic) { value in
        AxisGridLine()
        AxisValueLabel {
            if let intValue = value.as(Int.self) {
                Text(intValue, format: .currency(code: "USD"))
                    .padding(.leading, 25)
            }
        }
    }
}

输出: