DataSource class abstract

Interface for LocalWidgetBuilder to obtain data from arguments.

The interface exposes the v method, the argument to which is a list of keys forming a path to a node in the arguments expected by the widget. If the method's type argument does not match the value obtained, null is returned instead.

In addition, to fetch widgets specifically, the child and childList methods must be used, and to fetch event handlers, the handler method must be used.

The isList and isMap methods can be used to avoid inspecting keys that may not be present (e.g. before reading 15 keys in a map that isn't even present, consider checking if the map is present using isMap and short-circuiting the key lookups if it is not).

To iterate over a list, the length method can be used to find the number of items in the list.