我正在进行一些耗时的计算,以创建图表数据在后台线程上。
我最初使用GCD,但每次用户通过点击按钮过滤图表数据时,图表数据都需要重新计算。如果用户快速点击图表数据过滤按钮(高级用户),那么每个GCD调度异步完成后,图表就会循环绘制。
我意识到我无法使用GCD取消线程,因此我尝试实现一个OperationQueue
。
我在添加新操作到队列之前调用cancelAllOperations()
。
队列中的操作有时会出现异常,有时看起来它们被取消了,有时看起来已经完成的不是最近放入队列的操作。
我还遇到了取消正在执行操作的问题,因为当我在操作完成块中检查操作的.isCancelled属性时,它从未为真。
我真正想要的是,如果图表数据计算当前正在后台线程中进行,并且用户点击另一个过滤按钮并在后台线程上启动另一个图表计算,则先前的图表后台线程计算将被终止并“替换”为最近添加的操作。
这可能吗?下面是一些代码:
func setHistoricalChart() -> Void {
self.lineChartView.clear()
self.lineChartView.noDataText = "Calculating Historical Totals, Please Wait..."
self.historicalOperationsQueue.qualityOfService = .utility
self.historicalOperationsQueue.maxConcurrentOperationCount = 1
self.historicalOperationsQueue.name = "historical operations queue"
let historicalOperation = Operation()
historicalOperation.completionBlock = { [weak self] in
//dictionary of feeds, array of data for each feed
var valuesByFeed = [String:[String]?]()
var dates = [String:[String]?]()
var chartDataSets = [IChartDataSet]()
//get data and values from DataMOs in the activeFeeds
if (self?.activeFeeds.count)! > 0 {
//check if operation is cancelled
if historicalOperation.isCancelled {
return
}
for (key, feed) in (self?.activeFeeds)! {
dates[key] = feed?.datas?.flatMap({ Utils.formatUTCDateString(utcDateString: ($0 as! DataMO).utcDateString) })
valuesByFeed[key] = feed?.datas?
.sorted(by: { (($0 as! DataMO).utcDateString)! < (($1 as! DataMO).utcDateString)! })
.flatMap({ ($0 as! DataMO).value })
}
//Create Chart Data
for (key, valuesArray) in valuesByFeed {
var dataEntries = [ChartDataEntry]()
for (index, value) in (valuesArray?.enumerated())! {
let dataEntry = ChartDataEntry(x: Double(index), y: Double(value)!)
dataEntries.append(dataEntry)
}
let singleChartDataSet = LineChartDataSet(values: dataEntries, label: key)
singleChartDataSet.drawCirclesEnabled = false
switch key {
case "Solar":
singleChartDataSet.setColors(UIColor(red: 230/255, green: 168/255, blue: 46/255, alpha: 1))
singleChartDataSet.drawFilledEnabled = true
singleChartDataSet.fillColor = UIColor(red: 230/255, green: 168/255, blue: 46/255, alpha: 0.8)
break
case "Wind":
singleChartDataSet.setColors(UIColor(red: 73/255, green: 144/255, blue: 226/255, alpha: 1))
singleChartDataSet.drawFilledEnabled = true
singleChartDataSet.fillColor = UIColor(red: 73/255, green: 144/255, blue: 226/255, alpha: 0.8)
break
case "Battery":
singleChartDataSet.setColors(UIColor(red: 126/255, green: 211/255, blue: 33/255, alpha: 1))
singleChartDataSet.drawFilledEnabled = true
singleChartDataSet.fillColor = UIColor(red: 126/255, green: 211/255, blue: 33/255, alpha: 0.8)
break
case "Gen":
singleChartDataSet.setColors(UIColor(red: 208/255, green: 1/255, blue: 27/255, alpha: 1))
singleChartDataSet.drawFilledEnabled = true
singleChartDataSet.fillColor = UIColor(red: 208/255, green: 1/255, blue: 27/255, alpha: 0.8)
break
case "Demand":
singleChartDataSet.setColors(UIColor(red: 128/255, green: 133/255, blue: 233/255, alpha: 1))
singleChartDataSet.drawFilledEnabled = true
singleChartDataSet.fillColor = UIColor(red: 128/255, green: 133/255, blue: 233/255, alpha: 0.8)
break
case "Prod":
singleChartDataSet.setColors(UIColor(red: 241/255, green: 92/255, blue: 128/255, alpha: 1))
singleChartDataSet.drawFilledEnabled = true
singleChartDataSet.fillColor = UIColor(red: 241/255, green: 92/255, blue: 128/255, alpha: 0.8)
break
default:
break
}
chartDataSets.append(singleChartDataSet)
}
}
//check if operation is cancelled
if historicalOperation.isCancelled {
return
}
//set chart data
let chartData = LineChartData(dataSets: chartDataSets)
//update UI on MainThread
OperationQueue.main.addOperation({
if (self?.activeFeeds.count)! > 0 {
self?.lineChartView.data = chartData
} else {
self?.lineChartView.clear()
self?.lineChartView.noDataText = "No Feeds To Show"
}
})
}
historicalOperationsQueue.cancelAllOperations()
historicalOperationsQueue.addOperation(historicalOperation)
}