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A theme context centralizes color and typography values so that every component in the app reads from a single source of truth. When the user switches between light and dark mode, updating the context value triggers a re-render of all consuming components with the new colors — no prop drilling or manual updates required.

Start by defining two theme objects with the same keys. Using identical keys for both themes means every component can apply a color without knowing which mode is active — it just reads from the current theme object and both themes handle the rest.

Create a ThemeContext that holds the current theme object and a toggle function. The default value mirrors the shape of what the Provider will supply, making it safe to destructure in consumers even if the Provider is accidentally missing in tests.

The ThemeProvider manages a boolean isDark state and derives the active theme object from it. The toggleTheme function flips the boolean. Memoize the context value with useMemo so that a new object reference is only created when isDark actually changes.

Export a useTheme hook that wraps useContext(ThemeContext). Components call useTheme() for a clean, descriptive import instead of remembering to pass the context object. The hook also throws a helpful error if called outside a ThemeProvider.

Any component that reads from useTheme will automatically display the correct colors for the current mode. Pass the theme colors into inline styles or StyleSheet styles. When the theme toggles, all consuming components re-render with the new values.

Add a dark mode switch to the settings screen. The Switch component's value is isDark from the theme context, and onValueChange calls toggleTheme. No local state needed — the toggle directly controls the global theme state.

Save the user's theme preference to AsyncStorage so it survives app restarts. In ThemeProvider, load the saved preference in a useEffect on mount and initialize state accordingly. Save the new value in toggleTheme whenever the user switches modes.

React Native's useColorScheme hook returns the device's current color scheme ('light' or 'dark'). You can use this as the default theme instead of always starting in light mode. If the user has not explicitly set a preference, respecting the system setting gives the best out-of-the-box experience.

The navigation header can also respond to theme changes. Pass a function to screenOptions on the navigator that reads from the theme context and returns header style options. When the theme changes, the navigator re-evaluates the options and updates the header colors accordingly.

When loading the saved theme from AsyncStorage on startup, there is a brief moment before the preference is restored. Prevent a flash of the wrong theme by showing a splash screen or delaying navigation until the theme is loaded. Use an isThemeReady state in the provider and render null until it is true.

Test your understanding of theme context and dark mode from this lesson.

In this lesson you learned: define separate light and dark theme objects with matching keys, provide both the active theme and a toggleTheme function through context, and persist the theme preference to AsyncStorage and restore it on app startup. Next up we explore avoiding context performance pitfalls.