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.. _the-view-and-its-building-blocks:
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================================
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The View and Its Building Blocks
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================================
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A simple way to edit (or simply observe) the attribute values of a
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:term:`HasTraits` object in a GUI window is to call the object's
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configure_traits() [3]_ method. This method constructs and displays a window
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containing editable fields for each of the object's :term:`trait attribute`\ s.
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For example, the following sample code [4]_ defines the SimpleEmployee class,
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creates an object of that class, and constructs and displays a GUI for the
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pair: examples; configure_traits()
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.. _example-1-using-configure-traits:
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.. rubric:: Example 1: Using configure_traits()
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# configure_traits.py -- Sample code to demonstrate
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from traits.api import HasTraits, Str, Int
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class SimpleEmployee(HasTraits):
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sam = SimpleEmployee()
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sam.configure_traits()
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Unfortunately, the resulting form simply displays the attributes of the object
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**sam** in alphabetical order with little formatting, which is seldom what is
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.. figure:: images/ui_for_ex1.jpg
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:alt: Dialog box showing all attributes of SimpleEmployee in alphabetical order
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Figure 1: User interface for Example 1
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In order to control the layout of the interface, it is necessary to define a
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View object. A View object is a template for a GUI window or panel. In other
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words, a View specifies the content and appearance of a TraitsUI window or
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For example, suppose you want to construct a GUI window that shows only the
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first three attributes of a SimpleEmployee (e.g., because salary is confidential
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and the employee number should not be edited). Furthermore, you would like to
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specify the order in which those fields appear. You can do this by defining a
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View object and passing it to the configure_traits() method:
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.. index:: configure_traits(); view parameter, examples; View object
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.. _example-2-using-configure-traits-with-a-view-object:
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.. rubric:: Example 2: Using configure_traits() with a View object
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# configure_traits_view.py -- Sample code to demonstrate
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from traits.api import HasTraits, Str, Int
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from traitsui.api import View, Item
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class SimpleEmployee(HasTraits):
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view1 = View(Item(name = 'first_name'),
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Item(name = 'last_name'),
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Item(name = 'department'))
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sam = SimpleEmployee()
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sam.configure_traits(view=view1)
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The resulting window has the desired appearance:
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.. figure:: images/ui_for_ex2.jpg
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:alt: User interface showing only First name, Last name, and Department
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Figure 2: User interface for Example 2
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A View object can have a variety of attributes, which are set in the View
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definition, following any Group or Item objects.
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The sections on :ref:`contents-of-a-view` through :ref:`advanced-view-concepts`
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explore the contents and capabilities of Views. Refer to
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the *Traits API Reference* for details of the View class.
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Except as noted, all example code uses the configure_traits() method; a detailed
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description of this and other techniques for creating GUI displays from Views
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can be found in :ref:`displaying-a-view`.
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.. index:: View; contents
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.. _contents-of-a-view:
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The contents of a View are specified primarily in terms of two basic building
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blocks: Item objects (which, as suggested by Example 2, correspond roughly to
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individual trait attributes), and Group objects. A given View definition can
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contain one or more objects of either of these types, which are specified as
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arguments to the View constructor, as in the case of the three Items in Example
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The remainder of this chapter describes the Item and Group classes.
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.. index:: widget, control
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The simplest building block of a View is the :term:`Item` object. An Item
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specifies a single interface :term:`widget`, usually the display for a single
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trait attribute of a HasTraits object. The content, appearance, and behavior of
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the widget are controlled by means of the Item object's attributes, which are
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usually specified as keyword arguments to the Item constructor, as in the case
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of *name* in Example 2.
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The remainder of this section describes the attributes of the Item object,
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grouped by categories of functionality. It is not necessary to understand all of
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these attributes in order to create useful Items; many of them can usually be
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left unspecified, as their default values are adequate for most purposes.
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Indeed, as demonstrated by earlier examples, simply specifying the name of the
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trait attribute to be displayed is often enough to produce a usable result.
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The following table lists the attributes of the Item class, organized by
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functional categories. Refer to the *Traits API Reference* for details on the
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.. index:: attributes; Item, Item; attributes
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.. index:: name attribute, dock attribute; Item, emphasized attribute
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.. index:: export attribute; Item, height attribute; Item, image attribute; Item
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.. index:: item_theme attribute; Item, label attribute; Item
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.. index:: label_theme attribute; Item, padding attribute; Item
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.. index:: resizable attribute, show_label attribute, springy attribute; Item
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.. index:: width attribute; Item, format_str attribute, format_func attribute
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.. index:: editor attribute, style attribute; Item, enabled_when attribute; Item
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.. index:: visible_when attribute; Item, defined_when attribute; Item
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.. index:: has_focus attribute, tooltip attribute, help attribute; Item
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.. index:: help_id attribute; Item, id attribute; Item
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.. _attributes-of-item-by-category-table:
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.. rubric:: Attributes of Item, by category
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+----------+---------------------+---------------------------------------------+
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|Category |Attributes |Description |
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+==========+=====================+=============================================+
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|Content | * **name** |These attributes specify the actual data to |
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| | |be displayed by an item. Because an Item is |
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| | |essentially a template for displaying a |
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| | |single trait, its **name** attribute is |
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| | |nearly always specified. |
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+----------+---------------------+---------------------------------------------+
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|Display |* **dock** |In addition to specifying which trait |
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|format |* **emphasized** |attributes are to be displayed, you might |
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| |* **export** |need to adjust the format of one or more of |
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| |* **height** |the resulting widgets. |
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| |* **item_theme** |If an Item's **label** attribute is specified|
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| |* **label** |but not its name, the value of **label** is |
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| |* **label_theme** |displayed as a simple, non-editable string. |
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| |* **padding** |(This feature can be useful for displaying |
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| |* **resizable** |comments or instructions in a TraitsUI |
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| |* **show_label** |window.) |
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+----------+---------------------+---------------------------------------------+
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|Content |* **format_str** |In some cases it can be desirable to apply |
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|format |* **format_func** |special formatting to a widget's contents |
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| | |rather than to the widget itself. Examples of|
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| | |such formatting might include rounding a |
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| | |floating-point value to two decimal places, |
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| | |or capitalizing all letter characters in a |
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| | |license plate number. |
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+----------+---------------------+---------------------------------------------+
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|Widget |* **editor** |These attributes override the widget that is |
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|override |* **style** |automatically selected by TraitsUI. These |
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| | |options are discussed in |
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| | |:ref:`introduction-to-trait-editor-factories`|
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| | |:ref:`the-predefined-trait-editor-factories`.|
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+----------+---------------------+---------------------------------------------+
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|Visibility|* **enabled_when** |Use these attributes to create a simple form |
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|and status|* **visible_when** |of a dynamic GUI, which alters the display |
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| |* **defined_when** |in response to changes in the data it |
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| |* **has_focus** |contains. More sophisticated dynamic behavior|
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| | |can be implemented using a custom |
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| |.. TODO: Add examples|:term:`Handler` see |
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| | here |:ref:`controlling-the-interface-the-handler` |
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+----------+---------------------+---------------------------------------------+
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|User help |* **tooltip** |These attributes provide guidance to the user|
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| |* **help** |in using the user interface. If the **help** |
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| |* **help_id** |attribute is not defined for an Item, a |
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| | |system-generated message is used instead. The|
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| |.. TODO: Add sample |**help_id** attribute is ignored by the |
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| | help screen |default help handler, but can be used by a |
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| | |custom help handler. |
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+----------+---------------------+---------------------------------------------+
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|Unique |* **id** |The **id** attribute is used as a key for |
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|identifier| |saving user preferences about the widget. If |
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| | |**id** is not specified, the value of the |
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| | |**name** attribute is used. |
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+----------+---------------------+---------------------------------------------+
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.. index:: Label class, Heading class, Spring class
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pair: Item; subclasses
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.. _subclasses-of-item:
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The TraitsUI package defines the following subclasses of Item:
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These classes are intended to help with the layout of a TraitsUI View, and need
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not have a trait attribute associated with them. See the *Traits API Reference*
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.. _the-group-object:
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The preceding sections have shown how to construct windows that display a simple
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vertical sequence of widgets using instances of the View and Item classes. For
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more sophisticated interfaces, though, it is often desirable to treat a group of
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data elements as a unit for reasons that might be visual (e.g., placing the
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widgets within a labeled border) or logical (activating or deactivating the
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widgets in response to a single condition, defining group-level help text). In
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TraitsUI, such grouping is accomplished by means of the :term:`Group` object.
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Consider the following enhancement to Example 2:
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pair: configure_traits(); examples
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triple: View; Group; examples
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.. _example-3-using-configure-traits-with-a-view-and-a-group-object:
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.. rubric:: Example 3: Using configure_traits() with a View and a Group object
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# configure_traits_view_group.py -- Sample code to demonstrate
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from traits.api import HasTraits, Str, Int
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from traitsui.api import View, Item, Group
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class SimpleEmployee(HasTraits):
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employee_number = Str
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view1 = View(Group(Item(name = 'first_name'),
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Item(name = 'last_name'),
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Item(name = 'department'),
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label = 'Personnel profile',
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sam = SimpleEmployee()
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sam.configure_traits(view=view1)
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The resulting window shows the same widgets as before, but they are now enclosed
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in a visible border with a text label:
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.. figure:: images/ui_for_ex3.jpg
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:alt: User interface showing three fields enclosed in a border
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Figure 3: User interface for Example 3
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pair: contents; Group
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.. _content-of-a-group:
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The content of a Group object is specified exactly like that of a View object.
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In other words, one or more Item or Group objects are given as arguments to the
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Group constructor, e.g., the three Items in Example 3. [5]_ The objects
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contained in a Group are called the *elements* of that Group. Groups can be
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pair: attributes; Group
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.. _group-attributes:
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The following table lists the attributes of the Group class, organized by
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functional categories. As with Item attributes, many of these attributes can
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be left unspecified for any given Group, as the default values usually lead to
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acceptable displays and behavior.
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See the *Traits API Reference* for details of the Group class.
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.. index:: object attribute; Group, content attribute; Group
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.. index:: label attribute; Group, show_border attribute, show_labels attribute
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.. index:: show_left attribute, padding attribute; Group, layout attribute
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.. index:: selected attribute, orientation attribute, style attribute; Group
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.. index:: columns attribute, dock attribute; Group, dock_theme attribute
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.. index:: group_theme attribute, item_theme attribute; Group
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.. index:: label_theme attribute; Group, image attribute; Group
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.. index:: export attribute; Group, springy attribute; Group
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.. _attributes-of-group-by-category-table:
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.. rubric:: Attributes of Group, by category
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+----------+---------------------+---------------------------------------------+
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|Category |Attributes |Description |
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+==========+=====================+=============================================+
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|Content |* **object** |The **object** attribute references the |
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| |* **content** |object whose traits are being edited by |
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| | |members of the group; by default this is |
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| | |'object', but could be another object in the |
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| | |current context. The **content** attribute is|
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| | |a list of elements in the group. |
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+----------+---------------------+---------------------------------------------+
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|Display |* **columns** |These attributes define display options for |
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|format |* **dock** |the group as a whole. |
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| |* **dock_theme** | |
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| |* **group_theme** |.. index:: enabled_when attribute; Group |
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| |* **image** |.. index:: visible_when attribute; Group |
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| |* **item_theme** |.. index:: defined_when attribute; Group |
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| |* **label** |.. index:: help attribute; Group |
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| |* **label_theme** |.. index:: help_id attribute; Group |
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| |* **layout** |.. index:: id attribute; Group |
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| |* **orientation** | |
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| |* **selected** | |
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| |* **show_border** | |
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| |* **show_labels** | |
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| |* **show_left** | |
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+----------+---------------------+---------------------------------------------+
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|Visibility|* **enabled_when** |These attributes work similarly to the |
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|and status|* **visible_when** |attributes of the same names on the Item |
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| |* **defined_when** |class. |
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| | |.. TODO: Does Item-level or Group-level take |
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| | | precedence? Find out and document. |
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+----------+---------------------+---------------------------------------------+
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|User help |* **help** |The help text is used by the default help |
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| |* **help_id** |handler only if the group is the only |
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| | |top-level group for the current View. For |
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| | |example, suppose help text is defined for a |
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| | |Group called **group1**. The following View |
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| | |shows this text in its help window:: |
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| | |The following two do not:: |
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| | | View(group1, group2) |
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| | | View(Group(group1)) |
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| | |The **help_id** attribute is ignored by the |
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| | |default help handler, but can be used by a |
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| | |custom help handler. |
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| | |.. TODO: The document needs to include |
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| | | material on organizing Views via Groups, |
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| | | including the implied top-level group of |
412
| | | every View. If we do this earlier in the |
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| | | document, it will probably simplify this. |
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+----------+---------------------+---------------------------------------------+
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|Unique |* **id** |The **id** attribute is used as a key for |
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|identifier| |saving user preferences about the widget. If |
417
| | |**id** is not specified, the **id** values |
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| | |of the elements of the group are concatenated|
419
| | |and used as the group identifier. |
420
+----------+---------------------+---------------------------------------------+
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pair: subclasses; Group
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.. _subclasses-of-group:
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The TraitsUI package defines the following subclasses of Group, which are
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helpful shorthands for defining certain types of groups. Refer to the *Traits
432
API Reference* for details.
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.. index:: HGroup, HFlow, HSplit, Tabbed, VGroup, VFlow, VGrid, VFold, VSplit
436
.. _subclasses-of-group_table:
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.. rubric:: Subclasses of Group
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+-----------+------------------------------+-----------------------------------------+
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|Subclass |Description |Equivalent To |
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+===========+==============================+=========================================+
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|HGroup |A group whose items are laid |:samp:`Group(orientation='horizontal')` |
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| |out horizontally. | |
445
+-----------+------------------------------+-----------------------------------------+
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|HFlow |A horizontal group whose items|:samp:`Group(orientation='horizontal', |
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| |"wrap" when they exceed the |layout='flow', show_labels=False)` |
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| |available horizontal space. | |
449
+-----------+------------------------------+-----------------------------------------+
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|HSplit |A horizontal group with |:samp:`Group(orientation='horizontal', |
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| |splitter bars to separate it |layout='split')` |
452
| |from other groups. | |
453
+-----------+------------------------------+-----------------------------------------+
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|Tabbed |A group that is shown as a tab|:samp:`Group(orientation='horizontal' |
455
| |in a notebook. |layout='tabbed', springy=True)` |
456
+-----------+------------------------------+-----------------------------------------+
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|VGroup |A group whose items are laid |:samp:`Group(orientation='vertical')` |
458
| |out vertically. | |
459
+-----------+------------------------------+-----------------------------------------+
460
|VFlow |A vertical group whose items |:samp:`Group(orientation='vertical', |
461
| |"wrap" when they exceed the |layout='flow', show_labels=False)` |
462
| |available vertical space. | |
463
+-----------+------------------------------+-----------------------------------------+
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|VFold |A vertical group in which |:samp:`Group(orientation='vertical', |
465
| |items can be collapsed (i.e., |layout='fold', show_labels=False)` |
466
| |folded) by clicking their | |
468
+-----------+------------------------------+-----------------------------------------+
469
|VGrid |A vertical group whose items |:samp:`Group(orientation='vertical', |
470
| |are laid out in two columns. |columns=2)` |
471
+-----------+------------------------------+-----------------------------------------+
472
|VSplit |A vertical group with splitter|:samp:`Group(orientation='vertical', |
473
| |bars to separate it from other|layout='split')` |
475
+-----------+------------------------------+-----------------------------------------+
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.. rubric:: Footnotes
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.. [3] If the code is being run from a program that already has a GUI defined,
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then use edit_traits() instead of configure_traits(). These methods are
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discussed in more detail in Section 4.3.
484
.. [4] All code examples in this guide that include a file name are also
485
available as examples in the :file:`tutorials/doc_examples/examples`
486
subdirectory of the Traits docs directory. You can run them individually,
487
or view them in a tutorial program by running:
488
:program:`python` :file:`{Traits_dir}/tutorials/tutor.py` :file:`{Traits_dir}/docs/tutorials/doc_examples`
490
.. [5] As with Views, it is possible for a Group to contain objects of more than
491
one type, but it is not recommended.
added
removed
docs/source/traitsui_user_manual/view.rst
