How to preselect an item in a Kivy RecycleView? - python-3.x

Question

The code below displays a RecycleView filled with selectable lines. Initially, no item is selected. Pressing on one of the two buttons selects a line. My question is: how can we preselect an item so that one is selected at the dialog opening ?
A solution would be to be able to set a callback function whiqh is called after the RecycleView has been displayed, but how ?
# -*- coding: utf-8 -*-
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.recycleview import RecycleView
from kivy.uix.recycleview.views import RecycleDataViewBehavior
from kivy.uix.label import Label
from kivy.properties import BooleanProperty, StringProperty, NumericProperty
from kivy.uix.recycleboxlayout import RecycleBoxLayout
from kivy.uix.behaviors import FocusBehavior
from kivy.uix.recycleview.layout import LayoutSelectionBehavior
kv = """
<SelectableLabel>:
# Draw a background to indicate selection
canvas.before:
Color:
rgba: (0.4, 0.4, 0.4, 1) if self.selected else (0.5, 0.5, 0.5, 1)
Rectangle:
pos: self.pos
size: self.size
<KivyPlayer>:
canvas:
Color:
rgba: 0.3, 0.3, 0.3, 1
Rectangle:
size: self.size
pos: self.pos
orientation: 'vertical'
BoxLayout:
orientation: 'vertical'
BoxLayout:
Button:
id: next_track
text: "Next Track"
on_release: controller.select_next()
Button:
id: previous_track
text: "Previous Track"
on_release: controller.select_previous()
BoxLayout:
RecycleView:
id: media_list
viewclass: 'SelectableLabel'
scroll_type: ['bars', 'content']
scroll_wheel_distance: dp(114)
bar_width: dp(10)
SelectableRecycleBoxLayout:
id: controller
key_selection: 'selectable'
default_size: None, dp(56)
default_size_hint: 1, None
size_hint_y: None
height: self.minimum_height
orientation: 'vertical'
# multiselect: True
touch_multiselect: True
spacing: dp(2)
"""
Builder.load_string(kv)
class SelectableRecycleBoxLayout(FocusBehavior, LayoutSelectionBehavior,
RecycleBoxLayout):
''' Adds selection and focus behaviour to the view. '''
# required to forbid unselecting a selected item. An item can be unselected
# only by selecting another item
touch_deselect_last = BooleanProperty(False)
def get_nodes(self):
nodes = self.get_selectable_nodes()
if self.nodes_order_reversed:
nodes = nodes[::-1]
if not nodes:
return None, None
selected = self.selected_nodes
if not selected: # nothing selected, select the first
self.select_node(nodes[0])
return None, None
if len(nodes) == 1: # the only selectable node is selected already
return None, None
last = nodes.index(selected[-1])
self.clear_selection()
return last, nodes
def select_next(self):
last, nodes = self.get_nodes()
if not nodes:
return
if last == len(nodes) - 1:
self.select_node(nodes[0])
else:
self.select_node(nodes[last + 1])
def select_previous(self):
last, nodes = self.get_nodes()
if not nodes:
return
if not last:
self.select_node(nodes[-1])
else:
self.select_node(nodes[last - 1])
class SelectableLabel(RecycleDataViewBehavior, Label):
''' Add selection support to the Label '''
index = None
selected = BooleanProperty(False)
selectable = BooleanProperty(True)
def refresh_view_attrs(self, rv, index, data):
''' Catch and handle the view changes '''
self.index = index
return super(SelectableLabel, self).refresh_view_attrs(
rv, index, data)
def on_touch_down(self, touch):
''' Add selection on touch down '''
if super(SelectableLabel, self).on_touch_down(touch):
return True
if self.collide_point(*touch.pos) and self.selectable:
return self.parent.select_with_touch(self.index, touch)
def apply_selection(self, rv, index, is_selected):
''' Respond to the selection of items in the view. '''
self.selected = is_selected
if is_selected:
print("selection changed to {0}".format(rv.data[index]))
else:
print("selection removed for {0}".format(rv.data[index]))
class KivyPlayer(BoxLayout):
''' Main Kivy class for creating the initial BoxLayout '''
def __init__(self, **kwargs):
super(KivyPlayer, self).__init__(**kwargs)
# Set media_list data
self.ids.media_list.data = [{'text': str(x), 'selectable': True} for x in range(100)]
class KivyApp(App):
def build(self):
return KivyPlayer()
KivyApp().run()

Answer 1

In your KivyPlayer class, you can specify the selected node in the SelectableRecycleBoxLayout using the selected_nodes list:
class KivyPlayer(BoxLayout):
''' Main Kivy class for creating the initial BoxLayout '''
def __init__(self, **kwargs):
super(KivyPlayer, self).__init__(**kwargs)
# Set media_list data
self.ids.media_list.data = [{'text': str(x), 'selectable': True} for x in range(100)]
# specify pre-selected node by its index in the data
self.ids.controller.selected_nodes = [17]