Kivy Reloader

Hot reload your Kivy app on multiple Android phones, emulators and computer at the same time, in real-time.

This tool allows you to instantly update your Kivy app on multiple devices simultaneously by pressing Ctrl + S, without having to restart / recompile every time you make a change, saving your precious development time and effort.

Check out the Kivy School tutorial to learn how to use this tool, or follow the documentation below.

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I am too impatient to read the tutorial, I want to see it working RIGHT NOW!

Clone this project, open the folder on terminal and type:

1. git clone https://github.com/kivy-school/kivy-reloader
2. cd kivy-reloader
3. poetry shell
4. poetry install
5. Update the kivy-reloader.toml file with your phone IP and make sure HOT_RELOAD_ON_PHONE is set to true.
6. adb install bin/kivy_super_reloader-0.1-armeabi-v7a_arm64-v8a-debug.apk
7. python main.py

Keep calm and enjoy the Kivy Reloader! 😄

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Tutorial

Prerequisites

You must have followed our installation guide and you must have the basic tools installed and know how to use them:

• Poetry

• Pyenv

• Git

• Scrcpy

  Install Scrcpy

  You must install scrcpy on your computer. It comes with adb, so you don't need to install it separately.

  • Install scrcpy on your operating system: Linux, Windows or macOS. You will be able to control your device from your computer.

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How it works

Kivy Reloader is using Kaki under the hood, which uses watchdog to watch for file changes. You configure on kivy-reloader.toml the folders / files you want to watch for changes. When a change is detected on any of these files or folders, Kivy Reloader updates and reloads your app on all the devices you have configured (they need to be connected to the same network).

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How to setup

I recommend you to use poetry to install kivy-reloader.

1. Start the Poetry Wizard

Start a poetry project with the following command and follow the wizard instructions.

poetry init

After the wizard is finished, the pyproject.toml file will be created in the project directory.

2. Activate the virtual environment

Type poetry shell on the terminal and press enter.

poetry shell

3. Install the dependencies

Install the dependencies by typing poetry add kivy-reloader on the terminal and press enter.

poetry add kivy-reloader

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Configure Kivy Reloader

After installing kivy-reloader, on the project folder, type on the terminal kivy-reloader init.

kivy-reloader init

This is going to create two files on your project folder: kivy-reloader.toml and buildozer.spec. The first time you run kivy-reloader init, you will see on the terminal:

This is the kivy-reloader.toml file that has been created on your project folder.

Configure the kivy-reloader.toml file:

Every line has an explanation above. The most important constants on this file are:

1. PHONE_IPS: Put the IP of your phone here. You can find the IP of your Android phone on: Settings > About phone > Status > IP Address.
2. HOT_RELOAD_ON_PHONE: Set it to true to hot heload on your phone when you press Ctrl+S
3. FULL_RELOAD_FILES: This is a list of file names that will trigger a live reload (your Kivy app will restart) when they change.
4. WATCHED_FOLDERS_RECURSIVELY: This is a list of folder names, for example ["screens", "components"]. If any file inside these folders change, your Kivy app will hot reload.

The kivy-reloader init also creates a file called buildozer.spec on your project folder. It has the minimal buildozer.spec that you can use to make your app work with Kivy Reloader.

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How to use

Instead of importing from kivy.app, import from kivy_reloader.app. Start the app within an async event loop using trio.

On this tutorial we are going to show 3 possible different structures of your beautiful app.

Beautiful App structure 0 (beginner example):

If you are a super beginner in Kivy and just want to have a single file with a Kivy app.

├── main.py

Create a file main.py and paste this code:

import trio
from kivy.lang import Builder

from kivy_reloader.app import App

kv = """
Button:
    text: "Hello World"
"""


class MainApp(App):
    def build(self):
        return Builder.load_string(kv)


app = MainApp()
trio.run(app.async_run, "trio")

Beautiful App structure 1 (intermediate example):

• Create a file called main.py, a file called app.py and a folder called screens.

• Inside the screens folder, create two files: main_screen.kv and main_screen.py.

.
├── main.py
├── app.py
└── screens
    ├── main_screen.kv
    └── main_screen.py

main.py

import trio

from app import MainApp

app = MainApp()
trio.run(app.async_run, "trio")

app.py

from kivy_reloader.app import App
from screens.main_screen import MainScreen

class MainApp(App):
    def build(self):
        return MainScreen()

screens/main_screen.kv

<MainScreen>:
    BoxLayout:
        orientation: "vertical"
        Button:
            text: "Welcome to Kivy Reloader!"

screens/main_screen.py

import os

from kivy.uix.screenmanager import Screen

from kivy_reloader.utils import load_kv_path

main_screen_kv = os.path.join("screens", "main_screen.kv")
load_kv_path(main_screen_kv)


class MainScreen(Screen):
    pass

Beautiful App structure 2 (advanced example):

This is the recommended way of structuring your app.

• Create a file called main.py and a folder called beautifulapp.
• Inside the beautifulapp folder, create a file called __init__.py.
• Inside the beautifulapp folder, create a folder called screens.
• Inside the screens folder, create two files: main_screen.kv and main_screen.py.

.
├── beautifulapp
│   ├── __init__.py
│   └── screens
│       ├── main_screen.kv
│       └── main_screen.py
├── main.py

main.py:

import trio

from beautifulapp import MainApp

app = MainApp()
trio.run(app.async_run, "trio")

beautifulapp/__init__.py:

from beautifulapp.screens.main_screen import MainScreen
from kivy_reloader.app import App


class MainApp(App):
    def build(self):
        return MainScreen()

beautifulapp/screens/main_screen.kv

<MainScreen>:
    BoxLayout:
        orientation: "vertical"
        Button:
            text: "Welcome to Kivy Reloader!"

beautifulapp/screens/main_screen.py

import os

from kivy.uix.screenmanager import Screen

from kivy_reloader.utils import load_kv_path

main_screen_kv = os.path.join("beautifulapp", "screens", "main_screen.kv")
load_kv_path(main_screen_kv)


class MainScreen(Screen):
    pass

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Run your app

Type python main.py on the terminal and your app will start. You can see the logs on the terminal. When you change any file (from the watched folders you specified on the kivy-reloader.toml file), your app will reload.

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How to compile and hot reload on Android:

1. Connect your phone to the computer using a USB cable.
2. Enable developer options and enable USB debugging on your phone.
3. On the terminal, type kivy-reloader run:

kivy-reloader run

This is a CLI application that will:

• 1. Compile your app (generate .apk file) and deploy it on your phone.
• 2. Start scrcpy to mirror your phone screen on your computer and show the logs from your app on the terminal using logcat.
• 3. Create a .aab file that will be used to deploy your app on Google Play Store.
• 4. Restart the adb server for you if needed.

You can easily control the CLI application using ↑ or ↓ arrows, and press ENTER ↵ or → to select the option you want.

4. Choose the first option and Buildozer will compile the app (create a .apk file) and deploy it on your phone. Once the app is on your phone, run python main.py and the hot reload will be already working.

Just press Ctrl + S in any file inside screens folder or main.py and your app will be updated on computer and phone at the same time. (assuming you have configured the kivy-reloader.toml file correctly).

Contribution

If you have any idea or suggestion, please open an issue or a pull request.

Do you need help?

If you need help with Kivy Reloader, you can ask on Kivy Discord support channels. We'll be happy to help you.