数组不存储值

Question

我正在从解析后端取回值并使用它们创建一个数组，但其中没有存储任何内容。有人可以告诉我我做错了什么吗？该行：let dataEntry = ChartDataEntry(value: values[i], xIndex: i) 返回 "index is out of range"

    var fattyArray: [Double] = []

override func viewDidLoad() {
    super.viewDidLoad()

    let innerQuery = PFUser.query()
    innerQuery!.whereKey("objectId", equalTo: "VTieywDsZj")
    let query = PFQuery(className: "BodyFat")
    query.whereKey("UserID", matchesQuery: innerQuery!)
    query.findObjectsInBackgroundWithBlock {
        (percentages: [PFObject]?, error: NSError?) -> Void in
        if error == nil {
            print("Successful, \(percentages!.count) retrieved")
            if let percentage = percentages as [PFObject]! {
                for percentage in percentages! {
                    print(percentage["BodyFatPercentage"])
         self.fattyArray.append(percentage["BodyFatPercentage"].doubleValue)
                    print(self.fattyArray)
                }
            }
        } else {
            print("\(error?.userInfo)")
        }
    }

    let months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun"]
    let unitsSold = fattyArray

    setChart(months, values: unitsSold)

}

func setChart(dataPoints: [String], values: [Double]) {

    var dataEntries: [ChartDataEntry] = []

    for i in 0..<dataPoints.count {
        let dataEntry = ChartDataEntry(value: values[i], xIndex: i)
        dataEntries.append(dataEntry)
    }

Answer 1

这里有两个问题：

一个问题是 findObjectsInBackgroundWithBlock 异步运行，即 fattyArray 直到稍后才附加值。您应该将调用 setChart 的代码移动到 findObjectsInBackgroundWithBlock 闭包中。

query.findObjectsInBackgroundWithBlock { percentages, error in
    if error == nil {
        // build your array like you did in your question

        // but when done, call `setChart` here

        let months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun"]
        let unitsSold = fattyArray

        setChart(months, values: unitsSold)
    } else {
        print("\(error?.userInfo)")
    }
}

// but not here

// let months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun"]
// let unitsSold = fattyArray
//
// setChart(months, values: unitsSold)

您的 setChart 例程给您一个 "index is out of range" 错误，因为您正在遍历 dataPoints，但在 values 数组中查找值.我在这里看不到任何东西可以保证 months 中的条目数与 fattyArray.
中的条目数相同
很明显，如果你修复了第一点，它就更有可能起作用（因为在数据完全检索之前你实际上不会生成图表），但我仍然看不到这里任何保证 findObjectsInBackgroundWithBlock 将 return 至少六个条目的内容。

数组不存储值

Array not storing values

arrays

charts

parse-platform

swift2