Expo Config Plugin: Android Styles Modifier

An Expo Config Plugin to programmatically modify the native Android styles.xml file during the prebuild process.

Installation

npm install expo-config-plugin-android-styles
# or
yarn add expo-config-plugin-android-styles

Problem

Sometimes you need to customize native Android theme attributes that aren't directly exposed via React Native component props or standard Expo config options. Manually editing files in the android directory is discouraged in Expo managed projects.

Common examples include:

Changing the accent color of native dialogs like the DatePicker or TimePicker.
Setting a default android:windowBackground.
Overriding specific theme items for AppTheme or other styles.

Solution

This config plugin uses Expo's withAndroidStyles modifier to safely add or modify <item> tags within specified <style> tags in your android/app/src/main/res/values/styles.xml file.

Compatibility

Tested with Expo SDK 48+
Requires @expo/config-plugins >= 7.0.0 (this is a peer dependency that should be provided by your Expo project)
Requires expo-build-properties for native modifications

Usage

Using app.json

{
  "expo": {
    "plugins": [
      [
        "expo-config-plugin-android-styles",
        {
          "styles": [
            {
              "styleName": "DialogDatePicker.Theme",
              "itemName": "colorAccent",
              "itemValue": "#8f78aa",
              "parentTheme": "Theme.AppCompat.Light.Dialog"
            },
            {
              "styleName": "AppTheme",
              "itemName": "android:datePickerDialogTheme",
              "itemValue": "@style/DialogDatePicker.Theme"
            },
            {
              "styleName": "AppTheme",
              "itemName": "android:timePickerDialogTheme",
              "itemValue": "@style/DialogDatePicker.Theme"
            }
          ]
        }
      ]
    ]
  }
}

Using app.config.js

const withAndroidStylesModifier = require("expo-config-plugin-android-styles");

module.exports = ({ config }) => {
  return {
    ...config,
    plugins: [
      [
        withAndroidStylesModifier,
        {
          styles: [
            {
              styleName: "DialogDatePicker.Theme",
              itemName: "colorAccent",
              itemValue: "#8f78aa",
              parentTheme: "Theme.AppCompat.Light.Dialog",
            },
            {
              styleName: "AppTheme",
              itemName: "android:datePickerDialogTheme",
              itemValue: "@style/DialogDatePicker.Theme",
            },
            {
              styleName: "AppTheme",
              itemName: "android:timePickerDialogTheme",
              itemValue: "@style/DialogDatePicker.Theme",
            },
          ],
        },
      ],
    ],
  };
};

Configuration Options

The plugin accepts an options object with the following structure:

interface StyleConfig {
  styleName: string; // The name of the style to modify/create
  itemName: string; // The name of the item to add/modify
  itemValue: string; // The value to set for the item
  parentTheme?: string; // Optional parent theme for new styles
}

interface PluginOptions {
  styles: StyleConfig[]; // Array of style configurations to apply
}

Example: Customizing DatePicker/TimePicker Accent Color

To customize the DatePicker and TimePicker accent color:

[
  "expo-config-plugin-android-styles",
  {
    "styles": [
      {
        "styleName": "DialogDatePicker.Theme",
        "itemName": "colorAccent",
        "itemValue": "#8f78aa",
        "parentTheme": "Theme.AppCompat.Light.Dialog"
      },
      {
        "styleName": "AppTheme",
        "itemName": "android:datePickerDialogTheme",
        "itemValue": "@style/DialogDatePicker.Theme"
      },
      {
        "styleName": "AppTheme",
        "itemName": "android:timePickerDialogTheme",
        "itemValue": "@style/DialogDatePicker.Theme"
      }
    ]
  }
]

How it Works

This plugin hooks into the Expo prebuild process. It parses the existing styles.xml, allows you to programmatically add or modify style items using the configuration, and then writes the updated styles.xml back to the native android project directory.

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

MIT License