Basic DataView Implementation

docs/source/data_view.rst

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+Pyface DataViews
+=================
+
+The Pyface DataView API allows visualization of heirarchical and
+non-heirarchical tabular data.
+
+Data Models
+-----------
+
+Data to be viewed needs to be exposed to the DataView infrastructure by
+creating a data model for it.  This is a class that implements the
+interface of |AbstractDataModel|.
+
+A data model for a dictionary could be implemented like this::
+
+    class DictDataModel(AbstractDataModel):
+
+        data = Dict
+
+        index_manager = Instance(IntIndexManager, ())
+
+The index manager is an ``IntIndexManager`` because the data is
+non-heirarchical and this is more memory-efficient than the alternative
+``TupleIndexManager``.
+
+Data Structure
+~~~~~~~~~~~~~~
+
+The keys are displayed in the row headers, so each row has one column
+displaying the value::
+
+    def get_column_count(self, row):
+        return 1
+
+The data is non-heirarchical, so the root has children and no other
+rows have children::
+
+    def can_have_children(self, row):
+        if len(row) == 0:
+            return True
+        return False
+
+The number of child rows of the root is the length of the dictionary::
+
+    def get_row_count(self, row):
+        if len(row) == 0:
+            return len(self.data)
+        return 0
+
+Data Values
+~~~~~~~~~~~
+
+To get the values of the data model, we need to find the apprpriate value
+from the dictionary::
+
+    keys_header = Str("Keys")
+    values_header = Str("Values")
+
+    def get_value(self, row, column):
+        if len(row) == 0:
+            # this is a column header
+            if len(column) == 0:
+                # title of the row headers
+                return self.keys_header
+            else:
+                return self.values_header
+        else:
+            row_index = row[0]
+            key, value = list(self.data.items())[row_index]
+            if len(column) == 0:
+                # the is a row header, so get the key
+                return key
+            else:
+                return value
+
+In this case, all of the values are text, and read-only, so we can have a
+trait holding the value type, and return that for every item::
+
+    header_value_type = Instance(AbstractValueType)
+    key_value_type = Instance(AbstractValueType)
+    value_type = Instance(AbstractValueType)
+
+    def _default_header_value_type(self):
+        return TextValue(is_editable=False)
+
+    def _default_key_value_type(self):
+        return TextValue(is_editable=False)
+
+    def _default_value_type(self):
+        return TextValue(is_editable=False)
+
+    def get_value_type(self, row, column):
+        if len(row) == 0:
+            return self.header_value_type
+        elif len(column) == 0:
+            return self.key_value_type
+        else:
+            return self.value_type
+
+The default assumes that values representable as text, but if the values were
+ints, for example then the class could be instantiated with::
+
+    model = DictDataModel(value_type=IntValue(is_editable=False))
+
+The ``is_editable`` arguments are not strictly needed, as the default
+implementation of |can_set_value| returns False, but if we wanted to make the
+data model read-write we would need to write an implementation of
+|can_set_value| which returns True for editable items, and an implementation
+of |set_value| that updates the data in-place.  This would look something like::
+
+    def can_set_value(self, row, column):
+        return len(row) != 0 and len(column) != 0:
+
+    def set_value(self, row, column, value):
+        if self.can_set_value(row, column):
+            row_index = row[0]
+            key = list(self.data)[row_index]
+            self.data[key] = value
+            return True
+        return False
+
+Update Events
+-------------
+
+Finally, when the underlying data changes, the DataView infrastructure expects
+certain event traits to be fired.  If a value is changed, or the value type is
+updated, but the number of rows and columns is unaffected, then the
+``values_changed`` trait should be fired with a tuple of ``(start_row_index,
+start_column_index, end_row_index, end_column_index)``.  If a major change has
+occurred, or if the size, shape or layout of the data has changed, then
+the ``structure_changed`` event should be fired with a simple ``True`` value.
+
+So for example, if the value types change, only the displayed values need to be
+updated::
+
+    @observe('header_value_type.updated')
+    def header_values_updated(self, event):
+        self.values_changed = ([], [], [], [0])
+
+    @observe('key_value_type.updated')
+    def key_values_updated(self, event):
+        self.values_changed = ([0], [], [len(self.data) - 1], [])
+
+    @observe('value_type.updated')
+    def values_updated(self, event):
+        self.values_changed = ([0], [0], [len(self.data) - 1], [0])
+
+On the other hand, if the dictionary or its items change, then it is simplest
+to just indicate that the entire view needs updating::
+
+    @observe('data.items')
+    def data_updated(self, event):
+        self.structure_changed = True
+
+
+
+.. |AbstractDataModel| replace:: :py:class:`~pyface.data_view.abstract_data_model.AbstractDataModel`
+.. |can_set_value| replace:: :py:class:`~pyface.data_view.abstract_data_model.AbstractDataModel.can_set_value`
+.. |set_value| replace:: :py:class:`~pyface.data_view.abstract_data_model.AbstractDataModel.set_value`

examples/data_view/array_example.py

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+# (C) Copyright 2005-2020 Enthought, Inc., Austin, TX
+# All rights reserved.
+#
+# This software is provided without warranty under the terms of the BSD
+# license included in LICENSE.txt and may be redistributed only under
+# the conditions described in the aforementioned license. The license
+# is also available online at http://www.enthought.com/licenses/BSD.txt
+#
+# Thanks for using Enthought open source!
+
+from traits.api import Array, Instance
+
+from pyface.api import ApplicationWindow, GUI
+from pyface.data_view.data_models.array_data_model import ArrayDataModel
+from pyface.data_view.i_data_view_widget import IDataViewWidget
+from pyface.data_view.data_view_widget import DataViewWidget
+
+
+class MainWindow(ApplicationWindow):
+    """ The main application window. """
+
+    data = Array
+
+    data_view = Instance(IDataViewWidget)
+
+    def _create_contents(self, parent):
+        """ Creates the left hand side or top depending on the style. """
+
+        self.data_view = DataViewWidget(
+            parent=parent,
+            data_model=ArrayDataModel(data=self.data),
+        )
+        self.data_view._create()
+        return self.data_view.control
+
+    def _data_default(self):
+        import numpy
+        return numpy.random.uniform(size=(10000, 10, 10))*1000000
+
+
+# Application entry point.
+if __name__ == "__main__":
+    # Create the GUI (this does NOT start the GUI event loop).
+    gui = GUI()
+
+    # Create and open the main window.
+    window = MainWindow()
+    window.open()
+
+    # Start the GUI event loop!
+    gui.start_event_loop()