Sideband_CE/sbapp/kivymd/uix/behaviors/declarative_bahavior.py

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2022-10-02 17:16:59 +02:00
"""
Behaviors/Declarative
=====================
.. versionadded:: 1.0.0
.. raw:: html
<div style="position: relative; padding-bottom: 56.25%; height: 0; overflow: hidden; max-width: 100%; height: auto;">
<iframe
src="https://www.youtube.com/embed/_kiaJacLz8o"
frameborder="0"
allowfullscreen
style="position: absolute; top: 0; left: 0; width: 100%; height: 100%;">
</iframe>
</div>
As you already know, the Kivy framework provides the best/simplest/modern
UI creation tool that allows you to separate the logic of your application
from the description of the properties of widgets/GUI components.
This tool is named `KV Language <https://kivy.org/doc/stable/guide/lang.html>`_.
But in addition to creating a user interface using the KV Language Kivy allows
you to create user interface elements directly in the Python code.
And if you've ever created a user interface in Python code, you know how ugly
it looks. Even in the simplest user interface design, which was created using
Python code it is impossible to trace the widget tree, because in Python code
you build the user interface in an imperative style.
Imperative style
----------------
.. code-block:: python
from kivymd.app import MDApp
from kivymd.uix.bottomnavigation import MDBottomNavigation, MDBottomNavigationItem
from kivymd.uix.label import MDLabel
from kivymd.uix.screen import MDScreen
class Example(MDApp):
def build(self):
screen = MDScreen()
bottom_navigation = MDBottomNavigation(
panel_color="#eeeaea",
selected_color_background="#97ecf8",
text_color_active="white",
)
data = {
"screen 1": {"text": "Mail", "icon": "gmail"},
"screen 2": {"text": "Discord", "icon": "discord"},
"screen 3": {"text": "LinkedIN", "icon": "linkedin"},
}
for key in data.keys():
text = data[key]["text"]
navigation_item = MDBottomNavigationItem(
name=key, text=text, icon=data[key]["icon"]
)
navigation_item.add_widget(MDLabel(text=text, halign="center"))
bottom_navigation.add_widget(navigation_item)
screen.add_widget(bottom_navigation)
return screen
Example().run()
.. image:: https://github.com/HeaTTheatR/KivyMD-data/raw/master/gallery/kivymddoc/bottom-navigation-styles-programming.png
:align: center
Take a look at the above code example. This is a very simple UI. But looking
at this code, you will not be able to figure the widget tree and understand
which UI this code implements. This is named imperative programming style,
which is used in Kivy.
Now let's see how the same code is implemented using the KV language,
which uses a declarative style of describing widget properties.
Declarative style with KV language
----------------------------------
.. code-block:: python
from kivy.lang import Builder
from kivymd.app import MDApp
class Test(MDApp):
def build(self):
return Builder.load_string(
'''
MDScreen:
MDBottomNavigation:
panel_color: "#eeeaea"
selected_color_background: "#97ecf8"
text_color_active: "white"
MDBottomNavigationItem:
name: "screen 1"
text: "Mail"
icon: "gmail"
MDLabel:
text: "Mail"
halign: "center"
MDBottomNavigationItem:
name: "screen 2"
text: "Discord"
icon: "discord"
MDLabel:
text: "Discord"
halign: "center"
MDBottomNavigationItem:
name: "screen 3"
text: "LinkedIN"
icon: "linkedin"
MDLabel:
text: "LinkedIN"
halign: "center"
'''
)
Test().run()
.. image:: https://github.com/HeaTTheatR/KivyMD-data/raw/master/gallery/kivymddoc/bottom-navigation-styles-programming.png
:align: center
Looking at this code, we can now clearly see the widget tree and their properties.
We can quickly navigate through the components of the screen and quickly
change/add new properties/widgets. This is named declarative UI creation style.
But now the KivyMD library allows you to write Python code in a declarative style.
Just as it is implemented in Flutter/Jetpack Compose/SwiftUI.
Declarative style with Python code
----------------------------------
.. code-block:: python
from kivymd.app import MDApp
from kivymd.uix.bottomnavigation import MDBottomNavigation, MDBottomNavigationItem
from kivymd.uix.label import MDLabel
from kivymd.uix.screen import MDScreen
class Example(MDApp):
def build(self):
return (
MDScreen(
MDBottomNavigation(
MDBottomNavigationItem(
MDLabel(
text="Mail",
halign="center",
),
name="screen 1",
text="Mail",
icon="gmail",
),
MDBottomNavigationItem(
MDLabel(
text="Discord",
halign="center",
),
name="screen 2",
text="Discord",
icon="discord",
),
MDBottomNavigationItem(
MDLabel(
text="LinkedIN",
halign="center",
),
name="screen 3",
text="LinkedIN",
icon="linkedin",
),
panel_color="#eeeaea",
selected_color_background="#97ecf8",
text_color_active="white",
)
)
)
Example().run()
.. note:: The KivyMD library does not support creating Kivy widgets in Python
code in a declarative style.
But you can still use the declarative style of creating Kivy widgets in Python code.
To do this, you need to create a new class that will be inherited from the Kivy
widget and the :class:`~DeclarativeBehavior` class:
.. code-block:: python
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
from kivymd.app import MDApp
from kivymd.uix.behaviors import DeclarativeBehavior
class DeclarativeStyleBoxLayout(DeclarativeBehavior, BoxLayout):
pass
class Example(MDApp):
def build(self):
return (
DeclarativeStyleBoxLayout(
Button(),
Button(),
orientation="vertical",
)
)
Example().run()
Get objects by identifiers
--------------------------
In the declarative style in Python code, the ids parameter of the specified
widget will return only the id of the child widget/container, ignoring other ids.
Therefore, to get objects by identifiers in declarative style in Python code,
you must specify all the container ids in which the widget is nested until you
get to the desired id:
.. code-block::
from kivymd.app import MDApp
from kivymd.uix.boxlayout import MDBoxLayout
from kivymd.uix.button import MDRaisedButton
from kivymd.uix.floatlayout import MDFloatLayout
class Example(MDApp):
def build(self):
return (
MDBoxLayout(
MDFloatLayout(
MDRaisedButton(
id="button_1",
text="Button 1",
pos_hint={"center_x": 0.5, "center_y": 0.5},
),
id="box_container_1",
),
MDBoxLayout(
MDFloatLayout(
MDRaisedButton(
id="button_2",
text="Button 2",
pos_hint={"center_x": 0.5, "center_y": 0.5},
),
id="float_container",
),
id="box_container_2",
)
)
)
def on_start(self):
# {
# 'box_container_1': <kivymd.uix.floatlayout.MDFloatLayout>,
# 'box_container_2': <kivymd.uix.boxlayout.MDBoxLayout object>
# }
print(self.root.ids)
# <kivymd.uix.button.button.MDRaisedButton>
print(self.root.ids.box_container_2.ids.float_container.ids.button_2)
Example().run()
Yes, this is not a very good solution, but I think it will be fixed soon.
.. warning:: Declarative programming style in Python code in the KivyMD library
is an experimental feature. Therefore, if you receive errors, do not hesitate
to create new issue in the KivyMD repository.
"""
from kivy.properties import StringProperty
from kivy.uix.widget import Widget
class DeclarativeBehavior:
"""
Implements the creation and addition of child widgets as declarative
programming style.
"""
id = StringProperty()
"""
Widget ID.
:attr:`id` is an :class:`~kivy.properties.StringProperty`
and defaults to `''`.
"""
def __init__(self, *args, **kwargs):
super().__init__(**kwargs)
for child in args:
if issubclass(child.__class__, Widget):
self.add_widget(child)
if hasattr(child, "id") and child.id:
self.ids[child.id] = child