As of the latest release (10/04/2019) RadPieChart with a PieSeries having LabelBinding set to a property name, and ShowLabels set to True, with the list of data bound to ItemsSource containing one or more empty pie slices (a null in the list), causes a System.Reflection.TargetException to be thrown on load of the page containing the chart in iOS (this scenario works fine in UWP).
I am using the latest available Visual Studio 2019 (16.3.5) and the latest available Xamarin.Forms package (126.96.36.1998062) and testing on an iPad with iOS 13.1. The reason I need to have a null value in the list is so that the custom color palette I'm applying will always apply the same colors to the same data points (pie slices), even though in some cases, zero or one or two of the three pie slices will have no data value (and so should not appear in the chart, but still "use up" the corresponding color in the 3 colors of the palette).
In the 08/02/2019 release, this scenario worked fine in iOS (the 09/13/2019 release had the https://feedback.telerik.com/xamarin/1431067-chart-ios-invalidcastexception-is-thrown-when-the-chart-is-loaded issue, which is now resolved in the 10/04/2019 release, but which prevented my testing in iOS since in my app I had RadCartesianCharts on the same pages as the RadPieCharts).
The newly broken functionality in iOS could possibly be related to two other items that are marked completed:
https://feedback.telerik.com/xamarin/1366403-piechart-tooltip-behavior-is-not-working-properly (in 10/04/2019 release)
https://feedback.telerik.com/xamarin/1365842-chart-null-value-support (in R3 2018 SP release)
Using the RadPieChart and PieSeries (UI for Xamarin v2019.2.802.1 from NuGet), I can currently set the LabelBinding (or LabelFormat or LabelFormatter) to adjust the strings displayed in the labels on the slices of the pie chart, but unlike other chart controls, I currently have no way to modify the styling of those labels like I can in every other chart control I've used from Telerik UI for Xamarin.
It seems to me that it would be best to have more properties on the PieSeries class, like LabelFontSize, LabelFontAttributes, LabelFontFamily, LabelTextColor, and LabelMargin (Label prefix to distinguish from LegendTitleBinding could be kept or discarded as desired on some of these names).
LabelMargin would be particularly helpful to eliminate the UWP situation wherein currently all pie slice labels overlap with the outer lighter ring of the pie chart (see image from UWP). The others just seem needed to maintain a consistent appearance of charts within an app - if all my chart labels are dark blue and a different font size and style except for the not-style-able black labels in pie charts, that makes pie charts hard to incorporate without looking bad or forcing styling elsewhere to match the pie charts' fixed values.
If you have a Chart with BarSeries and TooltipBehavior defined, the tooltip of each bar is shown only when the user taps in the area around the tip of the bar.
The expected behavior is the tooltip to be displayed when clicking anywhere on the bar.
I would like to have support for selecting a slice of the piechart from code-behind. I have have looked into the chart and series properties but found no selectable datapoints property. The chartSelectionBehavior offers a ClearSelection method and the readonly SelectedPoints property, but nothing to add a selected point.
If we have a Chart with combined barseries and lineseries, and the lineseries is added first, the bars are misaligned - they are not placed in the center of the axis label on Android.
As a workaround, make sure to add first the barseries, then the lineseries.
When Custom Palette is used and FillColor is set, the color is not applied to the line series.
As a workaround set the both properties of the PaletteEntry: FillColor and SrtokeColor:
<telerikChart:PaletteEntry FillColor="Red" StrokeColor="Red" />