Select the data point programmatically and the highLight is NAN

[HsiaoAi]

I'd like to select the last data point programmatically and draw gradient background, but i get the highLight is NAN so I cant get the coordinate to draw the gradient.
I used :
chartView.highlightValue(Highlight(x: lastEntry.x, y: lastEntry.y, dataSetIndex: 0), callDelegate: true)
to select the last entry, and draw the gradient in the delegate function:
func chartValueSelected(_ chartView: ChartViewBase, entry: ChartDataEntry, highlight: Highlight) but the highlight is NAN.
I also tried using "valueToPixelMatrix" way to get the coordinate, but the results are different from the highlight.xPx and highlight.yPx,
i would like to ask how can i get the correct coordinate of data point on Chart View,
Thank you guys.

[jjatie]

Please note that for how-to's, ask on Stack Overflow. If you would like to file an issue or feature request, please fill out the form provided.