Defining CustomPropertyEditor at this time could be done only from code behind by defining platform specific code for both iOS and Android as it has been described in the documentation
. Also, this scenario has been demonstrated in the sample app her
e, which could be used for some further help.
However defining such an editor via XML could be a useful feature, that's why I logged new issue here
, where the other customers could also vote on it. If there is an interest, this feature could be included for some of the next UI for NativeScript versions.
Hope this information helps
Telerik by Progress