I have a pie chart that displays data added to it It looks like this:

class HomeViewController: UIViewController {

    var pieChart = PieChartView()

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        pieChart.delegate = self               
        self.setChart()
    }
    
    func setChart() {
        var entries: [ChartDataEntry] = []
                
        for entry in 0..<(self.cellArr.count) {
            if self.cellArr.count > 0 {
                let dataEntry = PieChartDataEntry(value: Double(self.cellArr[entry].amount), label: String(self.cellArr[entry].type))
                entries.append(dataEntry)
            }
        }
        updateSorting(values: entries)
    }
    
    func updateSorting(values: [ChartDataEntry]){
        let dataSet = PieChartDataSet(entries: values, label: "")
        let data = PieChartData(dataSets: [dataSet])
        
        dataSet.colors = ChartColorTemplates.colorful()
        pieChart.data = data
        pieChart.notifyDataSetChanged()        
    }
}

The problem is in the entries variable, which is located in the setChart function. I need to work with it outside the function, but if I put it in a class -

class HomeViewController: UIViewController {

    var pieChart = PieChartView()
    var entries: [ChartDataEntry] = [] // <------------ !!!

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        pieChart.delegate = self               
        self.setChart()
    }
}

Then the chart will start displaying extra values

An illustrative example:

enter image description here enter image description here

In the first screenshot, entries is in a function, in the second it is already behind it

I tried to set breakpoints and look at the for loop, but I still don’t understand why it happens that the array adds old data to new ones with each iteration

CodePudding user response：

Since you're calling setChart from viewWillAppear, you'll be appending to many items in your array (if the view appears/disappears in a single session). You need to clear the variables appropriately, or just overwrite them entirely.

Unrelated, but you can greatly simplify this for loop code:

Start:

func setChart1() {
    var entries: [ChartDataEntry] = []
            
    for entry in 0..<(self.cellArr.count) {
        if self.cellArr.count > 0 {
            let dataEntry = PieChartDataEntry(value: Double(self.cellArr[entry].amount), label: String(self.cellArr[entry].type))
            entries.append(dataEntry)
        }
    }
    updateSorting(values: entries)
}

Remove useless if statement:

func setChart2() {
    var entries: [ChartDataEntry] = []
            
    for entry in 0..<(self.cellArr.count) {
        let dataEntry = PieChartDataEntry(value: Double(self.cellArr[entry].amount), label: String(self.cellArr[entry].type))
        entries.append(dataEntry)
    }
    updateSorting(values: entries)
}

Replace manually constructed range of indices with a simple Array.indices:

func setChart3() {
    var entries: [ChartDataEntry] = []
            
    for entry in self.cellArr.indices { // "entry" is a total misnomer. It's not an entry, it's an index that can be used to get an entry
        let dataEntry = PieChartDataEntry(value: Double(self.cellArr[entry].amount), label: String(self.cellArr[entry].type))
        entries.append(dataEntry)
    }
    updateSorting(values: entries)
}

Realize that you don't even need the indices, you only actually care about the values themselves:

func setChart4() {
    var entries: [ChartDataEntry] = []
            
    for entry in self.cellArr {
        let dataEntry = PieChartDataEntry(value: Double(entry.amount), label: String(entry.type))
        entries.append(dataEntry)
    }
    updateSorting(values: entries)
}

Inline local variable (its name adds no useful information):

func setChart5() {
    var entries: [ChartDataEntry] = []
            
    for entry in self.cellArr {
        entries.append(PieChartDataEntry(value: Double(entry.amount), label: String(entry.type)))
    }
    updateSorting(values: entries)
}

Notice that this is just a map operation:

func setChart6() {
    var entries: [ChartDataEntry] = self.cellArr.map { entry in
        PieChartDataEntry(value: Double(entry.amount), label: String(entry.type)))
    }
    updateSorting(values: entries)
}

entries can now be immutable, and can use type inference:

func setChart7() {
    let entries = self.cellArr.map { PieChartDataEntry(value: Double($0.amount), label: String($0.type))) }
    updateSorting(values: entries)
}

CodePudding user response：

I put the array of entries into a class and cleared it in the setChart7 function

class HomeViewController: UIViewController {

    var pieChart = PieChartView()

    var entries: [ChartDataEntry] = []

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

    self.setChart()
    }

    func setChart7() {
        entries.removeAll()
        let entries = self.cellArr.map { PieChartDataEntry(value: Double($0.amount), label: String($0.type))) }
        updateSorting(values: entries)
    }
}