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delegating_handler.py

#-----------------------------------------------------------------------------
#
#  Copyright (c) 2006 by Enthought, Inc.
#  All rights reserved.
#
#-----------------------------------------------------------------------------

"""
A handler that delegates the handling of events to a set of sub-handlers.

This is typically used as the handler for dynamic views.  See the
**enthought.traits.has_dynamic_view** module.

"""


# Standard library imports.
import logging

# Enthought library imports.
from enthought.traits.api import HasTraits, List
from enthought.traits.ui.ui import Dispatcher

# Local imports.
from handler import Handler


# Setup a logger for this module.
logger = logging.getLogger(__name__)


00032 class DelegatingHandler(Handler):
    """
    A handler that delegates the handling of events to a set of sub-handlers.

    """

    ##########################################################################
    # Attributes
    ##########################################################################

    #### public 'DelegatingHandler' interface ################################

    # The list of sub-handlers this object delegates to.
    sub_handlers = List(HasTraits)


    #### protected 'DelegatingHandler' interface #############################

    # A list of dispatchable handler methods
    _dispatchers = List


    ##########################################################################
    # 'Handler' interface
    ##########################################################################

    #### public methods ######################################################

00060     def closed(self, info, is_ok):
        """
        Handles the user interface being closed by the user.

        This method is overridden here to unregister any dispatchers that were
        set up in the init() method.

        """

        for d in self._dispatchers:
            d.remove()

        return


00075     def init(self, info):
        """
        Initializes the controls of a user interface.

        Parameters
        ----------
        info : *UIInfo* object
            The UIInfo object associated with the view

        Returns
        -------
        A boolean, indicating whether the user interface was successfully
        initialized. A True value indicates that the UI can be displayed;
        a False value indicates that the display operation should be
        cancelled.

        Description
        -----------
        This method is called after all user interface elements have been
        created, but before the user interface is displayed. Use this method to
        further customize the user interface before it is displayed.

        This method is overridden here to delegate to sub-handlers.

        """

        # Iterate through our sub-handlers, and for each method whose name is
        # of the form 'object_name_changed', where 'object' is the name of an
        # object in the UI's context, create a trait notification handler that
        # will call the method whenever object's 'name' trait changes.
        logger.debug('Initializing delegation in DelegatingHandler [%s]', self)
        context = info.ui.context
        for h in self.sub_handlers:
            # fixme: I don't know why this wasn't here before... I'm not
            # sure this is right!
            h.init(info)

            for name in self._each_trait_method(h):
                if name[-8:] == '_changed':
                    prefix = name[:-8]
                    col = prefix.find( '_', 1 )
                    if col >= 0:
                        object = context.get(prefix[:col])
                        if object is not None:
                            logger.debug('\tto method [%s] on handler[%s]',
                                name, h)
                            method = getattr(h, name)
                            trait_name = prefix[col + 1:]
                            self._dispatchers.append(
                                Dispatcher(method, info, object, trait_name)
                                )

                            # Also invoke the method immediately so initial
                            # user interface state can be correctly set.
                            if object.base_trait(trait_name).type != 'event':
                                method(info)

                # fixme: These are explicit workarounds for problems with:-
                #
                # 'GeometryHierarchyViewHandler'
                #
                # which is used in the :-
                #
                # 'GeometryHierarchyTreeEditor'
                #
                # which are in the 'encode.cad.ui.geometry' package.
                #
                # The tree editor has dynamic views, and hence the handler gets
                # wrapped by a 'DelegatingHandler'. Unfortunately the handler
                # has a couple of methods that aren't picked up by the usual
                # wrapping strategy:-
                #
                # 1) 'tree_item_selected'
                #
                # - which is obviously called when a tree item is selected.
                #
                # 2) 'inspect_object'
                #
                # - which is called directly as as action from the context menu
                #   defined in the tree editor.
                #
                elif name in ['tree_item_selected', 'inspect_object']:
                    self.__dict__[name] = self._create_delegate(h, name)

        return True

00161     def _create_delegate(self, h, name):
        """ Quick fix for handler methods that are currently left out! """

        def delegate(*args, **kw):
            method = getattr(h, name)
            return method(*args, **kw)

        return delegate

#### EOF #####################################################################


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