如何使用ios-charts在饼图视图中获取选定切片的索引?

I can't figure out how to make a UILabel visible if a slice is selected in a Pie Chart View. I need to know how to identify if a slice was selected and then what slice was selected so I can put the right text in a UILabel and then unhide the label. I can't figure out how to make a UILabel visibl