When a mandatory property has not filled in, the control should go red as per every application/website on the planet. How do we do this in Xamarin Forms?
In Silverlight/WPF and probably UWP, the INotifyDataErrorInfo interface can be implemented so that controls can be notified when errors occur, and then through binding the UI reflects that an error has occurred which relates to the property that the control is bound to. Does this functionality exist in Xamarin Forms? Will it ever exist?
Note: it's not enough to simply supply some validation metadata like adding an attribute to a property that means that the property is mandatory. Each of our customers has customized business logic and fields may only become mandatory in certain situations. For example, there will be cases where field X is only mandatory when fields Y and Z are also filled in.