Charts are broken with Xcode 27, Plotting multiple lines

When will there be a bug fix?

This works

var dataMultiLine: [LocationData.Series] {
    LocationData.last30Days
}

struct MultiLineView: View {
    var body: some View {
        VStack {
            Chart {
                ForEach(dataMultiLine) { series in
                    ForEach(series.sales, id: \.day) { element in
                        LineMark(
                            x: .value("Day", element.day, unit: .day),
                            y: .value("Sales", element.sales)
                        )
                    }
                    .foregroundStyle(by: .value("City", series.city))
                    .symbol(by: .value("City", series.city))
                    .interpolationMethod(.catmullRom)
                }
            }
        }
        .padding()
    }
}

This doesn't work

var dataContent: [MonthlyHoursOfSunshine] = [
    MonthlyHoursOfSunshine(city: "Cupertino", month: 1, hoursOfSunshine: 196),
    MonthlyHoursOfSunshine(city: "Seattle", month: 1, hoursOfSunshine: 74),
    MonthlyHoursOfSunshine(city: "Seattle", month: 12, hoursOfSunshine: 62),
    MonthlyHoursOfSunshine(city: "Cupertino", month: 12, hoursOfSunshine: 199),
]

struct ContentView: View {
    var body: some View {
        VStack {
            Chart(dataContent) {
                    LineMark(
                        x: .value("Month", $0.date),
                        y: .value("Hours of Sunshine", $0.hoursOfSunshine)
                    )
                    .foregroundStyle(by: .value("City", $0.city))
                    .symbol(by: .value("City", $0.city))
                }
        }
        .padding()
    }
}

Christian

Please consider filing a bug report about this so our engineering teams can investigate this issue. A resolution may involve changes to Apple's software. If you post the Feedback number here I'll check the status next time I do a sweep of forums posts where I've suggested bug reports.

Bug Reporting: How and Why? has tips on creating your bug report.

Hi,

thanks for the tip about the bug report. I thought the forum was also for reporting bugs.

The Bug Report number is FB25050954

Christian

Thanks for filing FB25050954 and for posting both versions of your chart. The Charts team has looked at the report.

The difference between your two versions is in the identifiers. I tested in macOS 27.0.1 and the iOS 27.0 simulator. When points in different cities share an id, a flat Chart(data) draws one line or none. An id based on the month or date causes this. In macOS 27.0.1, giving every data point its own id draws both lines from the same four points, in either order.

The init(_:content:) documentation says: "This initializer wraps the data that you provide as input in an implicit ForEach structure. If you need to represent more than one series in your chart, use init(content:) instead." Your nested ForEach version follows that route.

If you'd rather keep your existing flat array, an identifier change made it draw every line in my testing. Either of these gives each point its own identifier:

// One identifier for each city and month.
var id: String { "\(city)-\(date)" }

// A separate identity for every entry, even two entries with identical values.
let id = UUID()

A UUID identifier changes each time you create the array, so it suits data that keeps the same instances between updates.

If your MonthlyHoursOfSunshine already has an identifier that's unique for every data point and lines still go missing, please add that detail to FB25050954.

Hi,

as I already mentioned in my first post—including a link to the Apple website—the example is not my own code; it comes from Apple itself.

The example worked prior to version 27, which is why I formatted my data in exactly that way; it ran without any issues until version 27.

I have already structured my data differently, though I might adjust it again.

For now, however, I am occupied with other SwiftUI bugs—for instance, NavigationSplitView, endless loop detail<->content

Unfortunately, no one has responded to the post yet.

I wanted to wait for a response before submitting a bug report, in case the procedure I’m following is incorrect.

Christian