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