# Simple Android App with Kivy

This guide demonstrates how to create a simple Android application using **Kivy**. Kivy is an open-source Python library for rapid development of applications that make use of innovative user interfaces, such as multi-touch apps. To package the app for Android, we use **Buildozer**.

**Modules Used:**
*   `kivy`: The framework for building the app UI and logic.

## Prerequisites

1.  **Python**: Installed on your development machine.
2.  **Linux Environment**: Buildozer (the packaging tool) works best on Linux. If you are on Windows, use **WSL2** (Windows Subsystem for Linux) or a Virtual Machine.

## Installation

Install Kivy on your development machine to test the app:

```bash
pip install kivy
```

## The Code

Save this as `main.py`. Kivy applications usually require the main file to be named `main.py` for packaging.

```python
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label
from kivy.uix.button import Button

class MyAndroidApp(App):
    def build(self):
        # 1. Main Layout
        # BoxLayout arranges widgets in a vertical or horizontal box
        layout = BoxLayout(orientation='vertical', padding=20, spacing=10)

        # 2. Label Widget
        self.label = Label(
            text="Hello, Android!",
            font_size='30sp',
            color=(1, 1, 1, 1) # White
        )
        layout.add_widget(self.label)

        # 3. Button Widget
        btn = Button(
            text="Click Me",
            size_hint=(1, 0.2), # Width: 100%, Height: 20% of parent
            background_color=(0, 0.5, 1, 1) # Blueish
        )
        # Bind the button press to a function
        btn.bind(on_press=self.on_button_click)
        layout.add_widget(btn)

        return layout

    def on_button_click(self, instance):
        self.label.text = "You clicked the button!"
        self.label.color = (0, 1, 0, 1) # Change text to Green

if __name__ == '__main__':
    MyAndroidApp().run()
```

## Testing Locally

You can run this script on your computer to test the UI logic before packaging.

```bash
python main.py
```

## Packaging for Android (Buildozer)

To turn this `main.py` into an `.apk` file that runs on Android, follow these steps in your **Linux/WSL** environment.

1.  **Install Buildozer Dependencies**:
    ```bash
    sudo apt update
    sudo apt install -y git zip unzip openjdk-17-jdk python3-pip autoconf libtool pkg-config zlib1g-dev libncurses5-dev libncursesw5-dev libtinfo5 cmake libffi-dev libssl-dev
    pip3 install --user --upgrade buildozer
    ```

2.  **Initialize Buildozer**:
    Navigate to the directory containing your `main.py` and run:
    ```bash
    buildozer init
    ```
    This creates a `buildozer.spec` file. You can edit this file to change the app name, package domain, permissions, etc.

3.  **Build the APK**:
    Connect your Android phone via USB (ensure USB Debugging is enabled) and run:
    ```bash
    # Build, deploy, and run the app on the connected device
    buildozer android debug deploy run
    ```
    
    *Note: The first build will take a long time as it downloads the Android SDK/NDK.*

    If you just want the APK file without deploying:
    ```bash
    buildozer android debug
    ```
    The `.apk` file will be in the `bin/` directory.

## Usage

Once installed on your phone, tap the app icon to launch it. It will display the label and button defined in your Python script.

[[programming/python/python]]