Tips, Tricks and Gotchas¶
Getting and Setting Model View Elements¶
For some applications, it can be necessary to retrieve or manipulate the View objects associated with a given model object. The HasTraits class defines two methods for this purpose: trait_views() and trait_view().
The trait_views() method, when called without arguments, returns a list
containing the names of all Views defined in the object’s class. For example, if
sam is an object of type SimpleEmployee3 (from
the method call
sam.trait_views() returns the list
Alternatively, a call to
trait_views(view_element_type) returns a list
of all named instances of class view_element_type defined in the object’s
class. The possible values of view_element_type are:
trait_views(View) is identical to calling
Note that the call
sam.trait_views(Group) returns an empty list, even though
both of the Views defined in SimpleEmployee contain Groups. This is because only
named elements are returned by the method.
Group and Item are both subclasses of ViewSubElement, while ViewSubElement and
View are both subclasses of ViewElement. Thus, a call to
trait_views(ViewSubElement) returns a list of named Items and Groups, while
trait_views(ViewElement) returns a list of named Items, Groups and Views.
The trait_view() method is used for three distinct purposes:
- To retrieve the default View associated with an object
- To retrieve a particular named ViewElement (i.e., Item, Group or View)
- To define a new named ViewElement
obj.trait_view()returns the default View associated with object obj. For example,
sam.trait_view()returns the View object called
traits_view. Note that unlike trait_views(), trait_view() returns the View itself, not its name.
obj.trait_view('my_view')returns the view element named
my_view(or None if
my_viewis not defined).
obj.trait_view('my_group', Group('a', 'b'))defines a Group with the name
my_group. Note that although this Group can be retrieved using
trait_view(), its name does not appear in the list returned by
traits_view(Group). This is because
my_groupis associated with obj itself, rather than with its class.