1#  Copyright (c) 2008-19, Enthought, Inc.
2#  All rights reserved.
3#
4#  This software is provided without warranty under the terms of the BSD
5#  license included in LICENSE.txt and may be redistributed only
6#  under the conditions described in the aforementioned license.  The license
7#  is also available online at http://www.enthought.com/licenses/BSD.txt
8#
9#  Thanks for using Enthought open source!
10#
11#  Author: David C. Morrill
12#  Date:   08/18/2008
13
14"""
15Defines some helper classes and traits used to define 'bindable' editor
16values.  These classes and associated traits are designed to simplify
17writing editors by allowing the editor factory to specify a context value
18instance for attributes and have the value on the editor be synchronized
19with the corresponsing value rom the context.
20
21The factory should look something like this::
22
23    class MyEditorFactory(EditorFactory):
24
25        #: The minimum value.
26        minimum = CVInt
27
28        #: The suffix for the data.
29        suffix = CVType(Str)
30
31The editor class needs to have traits which correspond to the context value
32traits, and should be able to react to changes to them::
33
34    class MyEditor(Editor):
35
36        #: The minimum value.
37        minimum = Int()
38
39        #: The suffix for the data.
40        suffix = Str()
41
42This can then be used in views, with values either as constants or as
43instances of :class:`ContextValue` (abbreviated as ``CV``)::
44
45    class MyObject(HasTraits):
46
47        #: An important value.
48        my_value = Str()
49
50        #: The minimum value.
51        my_minimum = Int(10)
52
53        traits_view = View(
54            Item(
55                'my_value',
56                editor=MyEditorFactory(
57                    minimum=CV('my_minimum'),
58                    suffix='...',
59                ),
60            )
61        )
62"""
63
64
65from traits.api import HasStrictTraits, Instance, Str, Int, Float, Either
66
67
68class ContextValue(HasStrictTraits):
69    """ Defines the name of a context value that can be bound to an editor
70
71    Resolution of the name follows the same rules as for context values in
72    Item objects: if there is no dot in it then it is treated as an
73    attribute of the 'object' context value, other wise the first part
74    specifies the object in the context and the rest are dotted attribute
75    look-ups.
76    """
77
78    #: The extended trait name of the value that can be bound to the editor
79    #: (e.g. 'selection' or 'handler.selection'):
80    name = Str()
81
82    # ------------------------------------------------------------------------
83    # object Interface
84    # ------------------------------------------------------------------------
85
86    def __init__(self, name):
87        super(ContextValue, self).__init__(name=name)
88
89
90#: Define a shorthand name for a ContextValue:
91CV = ContextValue
92
93
94# Trait definitions useful in defining bindable editor traits ---------------
95
96
97def CVType(type, **metadata):
98    """ Factory that creates a union of a trait type and a ContextValue trait.
99
100    This also sets up one-way synchronization to the editor if no
101    other synchronization is specified.
102
103    Parameters
104    ----------
105    type : trait type
106        The trait type that is expected for constant values.
107    **metadata
108        Additional metadata for the trait.
109
110    Returns
111    -------
112    cv_type_trait : trait
113        A trait which can either hold a constant of the specified
114        type or an instance of the ContextValue class.
115    """
116    metadata.setdefault("sync_value", "to")
117    return Either(type, InstanceOfContextValue, **metadata)
118
119
120#: Shorthand for an Instance of ContextValue trait.
121InstanceOfContextValue = Instance(ContextValue, allow_none=False)
122
123#: Int or Context value trait
124CVInt = CVType(Int)
125
126#: Float or Context value trait
127CVFloat = CVType(Float)
128
129#: Str or Context value trait
130CVStr = CVType(Str)
131