IDataErrorInfo與DataErrorValidationRule

IDataErrorInfo與DataErrorValidationRule 

this[key] is in fact an indexer, and is somewhat of a cross between a property and a method. It acts like a property since you can bind to it, but as opposed to regular properties, it receives a parameter.

Behind the scenes it's implemented as a method - get_Item(key), and if you'd want to access it via reflection you'd need to use Item for a name. For example:

typeof(MyClass).GetProperty("Item");

This is also important to know when implementing INotifyPropertyChanged, in which case,"Item[]" or Binding.IndexerName should be used as a property name in order to update the UI.