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How to use .kv file in kivy

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by vsasikalabe dot icon Updated: Aug 29, 2023

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Kivy has the KV design language. It is thought of as a language like HTML and CSS. It handles styling and adding elements to the display but does not handle any logic. 

 

The KV language is sometimes called kvlang or the kivy language. It allows you to create your widget tree. You can use it to connect widget properties or callbacks and make statements. However, it depends on the development environment. You can pick a Kivy installation that works with your development environment. Developers use different widgets and canvas instructions to build Kivy widgets.   

 

You can create many kv files. Also, you can include it in one place (root file). You can distribute/branch your code Kivy documentation. A kv file will contain only one root widget; most means only one kv main file. Whenever we define the id attribute in a KV file, it will not be available on the widget instance. Instead, it will be on weakref to the widget. A Kivy rule will apply to a specific widget.  

 

The KV file changes the widget. It specifies how it behaves or adds a visual representation. The KV language also supports importing Python modules in KV, creating dynamic classes. You can also parse and load Kv language in a multi-line string in your Python file. By default, Kivy loads the kv file that will match the prefix of the app class defined in the Python script.  

 

A Kivy dynamic class allows you to create new widgets or rules. You create this without making any Python declaration. Root widgets are the building blocks of GUIs in Kivy, and a KV file can contain only one root widget. Use the args keyword to access the arguments in the on_<action> callback methods.   

  

Because BoxLayout is a sub-class of Layout and Widget. It inherits many other methods and keyword arguments. If the Root Widget defines this file, it will attach to the App's root attribute. The application widget tree uses it as the base. The App class calls the build method and returns either a widget or an instance of the Builder class.   

Fig : Preview of the output that you will get on running this code from your IDE.

Code

In this solution, we used Kivy library of Python.

Use kivy widget made in python in .kv file

PythondotLines of Code : 31dotLicense : Strong Copyleft (CC BY-SA 4.0)

Dependent Libraries : 
#Main.py:
from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.widget import Widget
from kivy.uix.button import Button
class WindowManager(ScreenManager):
    pass
class MainWindow(Screen):
    def on_enter(self, *args):
        self.add_widget(Button(text="Test button made in PY file",size_hint=(1, .5),pos_hint={"x": 0, "top": .5}))
class KvWidget(Widget):
    pass
class MyApp(App):
    def build(self):
        return WindowManager()
if __name__ == "__main__":
    MyApp().run()

<WindowManager>:
    MainWindow:
<MainWindow>:
    KvWidget:
<KvWidget>:
    FloatLayout:
        size: root.width, root.height

        Button:
            text: "Test Button made in KV file"
            size_hint: 1, .5
            pos_hint: {"x": 0, "top": 1}

Instructions

Follow the steps carefully to get the output easily.

  1. Download and Install the PyCharm Community Edition on your computer.
  2. Open the terminal and install the required libraries with the following commands.
  3. Install Kivy - pip install Kivy
  4. Create a new Python file on your IDE.
  5. Copy the snippet using the 'copy' button and paste it into your Python file.
  6. Create my.kv file and paste windowManager to end.
  7. Run the current file to generate the output.


I hope you found this useful.


I found this code snippet by searching for ' Use kivy widget made in python in .kv file' in Kandi. You can try any such use case!

Environment Tested

I tested this solution in the following versions. Be mindful of changes when working with other versions.

  1. PyCharm Community Edition 2022.3.1
  2. The solution is created in Python 3.11.1 Version
  3. Kivy 2.2.1 Version


Using this solution, we can able to use .kv file in Kivy with simple steps. This process also facilities an easy way to use, hassle-free method to create a hands-on working version of code which would help us to use .kv file in Kivy.

Dependent Libraries

kivyby kivy

Python doticonstar image 15962 doticonVersion:2.2.0doticon
License: Permissive (MIT)

Open source UI framework written in Python, running on Windows, Linux, macOS, Android and iOS

Support
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          Reuse

            kivyby kivy

            Python doticon star image 15962 doticonVersion:2.2.0doticon License: Permissive (MIT)

            Open source UI framework written in Python, running on Windows, Linux, macOS, Android and iOS
            Support
              Quality
                Security
                  License
                    Reuse

                      If you do not have keras, and Numpy libraries that are required to run this code, you can install them by clicking on the above link.

                      You can search for any dependent library on Kandi like Kivy.

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                      1. For any support on Kandi solution kits, please use the chat
                      2. For further learning resources, visit the Open Weaver Community learning page

                      FAQ:   

                      1. What is a Kivy.kv file, and how does it work in a Kivy application?   

                      The KV language allows us to create our widget tree declaratively. It is to bind the widget properties to each other or callbacks naturally.   

                         

                      2. How can I create the root widget for my application widget tree?   

                      The runApp() function will take the given widget. It will make it the root of the widget tree. The widget tree consists of two widgets: the Center widget and its child, the Text widget. The framework forces the root widget to cover the screen. The text "Hello, world" centers on the screen.   

                         

                      3. Which programming language is used to write code inside the Kivy kv file?   

                      If we write the application in Python Kivy, writing all the things in the same code makes a mess in the code. It is hard to understand that by someone else. Writing much code can make organizing the widget tree, especially the bindings, difficult.   

                         

                      4. How do I write button code inside the Kivy kv file?   

                      • import kivy, kivyApp   
                      • import button, float layout.   
                      • set least version(optional)   
                      • Create the Layout class.   
                      • Create App class.   
                      • Create .kv file:   
                      • Add Base class.   
                      • Add Button properties.   
                      • Add the Image as a button.   
                      • Round the corners of the button using the border property   
                      • Return instance of the layout class.   
                      • Run an instance of the class.   

                        

                      5. Is there any advantage to storing all your information in a single file such as Kivy.kv?   

                      • Given its library-rich nature, Python serves as a powerful foundation.   
                      • Write code once and use it across all devices.   
                      • Easy-to-use widgets built with multi-touch support.   
                      • Performs better than HTML5 cross-platform alternatives.  

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