'valueForSeries' doesn't exist anymore

Hi,
As said in the title, I try to use this function to get a vertical line showing value

func didTouchChart(chart: Chart, indexes: Array, x: Float, left: CGFloat) {
for (serieIndex, dataIndex) in enumerate(indexes) {
if dataIndex != nil {
// The series at serieIndex has been touched
let value = chart.**valueForSeries**(serieIndex, atIndex: dataIndex)
}
}
}

But Xcode give me an error. Any clue to fix that ?

Thanks!