Light/Dark Theme (Java)

Android has built-in support for day/night theming — an app can define one set of colors for light mode and a completely different set for dark mode, and the system automatically shows the right one based on the device's current setting. This is the same resource-qualifier idea introduced in Resources Overview, applied specifically to night mode.

1. Light and Dark Color Resources

The default res/values/colors.xml holds your light-mode colors, exactly as usual. A parallel folder, res/values-night/colors.xml, defines resources with the same names but dark-mode-appropriate values. Android picks whichever file matches the active system setting — no code required to switch between them.

<!-- res/values/colors.xml (light mode) -->
<resources>
    <color name="screen_background">#FFFFFF</color>
    <color name="primary_text">#1A1A1A</color>
    <color name="card_background">#F5F5F5</color>
</resources>

<!-- res/values-night/colors.xml (dark mode) -->
<resources>
    <color name="screen_background">#121212</color>
    <color name="primary_text">#EEEEEE</color>
    <color name="card_background">#1E1E1E</color>
</resources>

<!-- RecipeBox's recipe detail screen root layout -->
<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/screen_background">

    <TextView
        android:id="@+id/tvRecipeTitle"
        android:textColor="@color/primary_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</LinearLayout>

2. Letting the User Override the System Setting

Some users want an app to always stay dark, regardless of their phone's overall setting; others want to follow the system automatically. AppCompatDelegate.setDefaultNightMode() lets your app apply that choice at runtime, overriding — or following — the device setting.

// SettingsActivity.java — a Light / Dark / System Default toggle
public class SettingsActivity extends AppCompatActivity {

    private RadioGroup themeGroup;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_settings);

        themeGroup = findViewById(R.id.rgTheme);

        themeGroup.setOnCheckedChangeListener((group, checkedId) -> {
            if (checkedId == R.id.rbLight) {
                AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO);
            } else if (checkedId == R.id.rbDark) {
                AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);
            } else {
                AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM);
            }
        });
    }
}

3. Testing Dark Mode

You don't need to keep flipping your phone's system setting to check both themes. Android Studio's Layout Editor preview panel has a "Night" toggle that renders the same layout with the values-night resources applied, letting you compare light and dark side by side. The emulator also has a quick-settings toggle for dark theme, and on a physical device it's under system Display settings — useful for a final check, but the in-editor preview is faster during day-to-day layout work.

4. android:forceDarkAllowed — An Older Approach

Android briefly offered android:forceDarkAllowed="true" on the app theme, which asked the system to automatically darken an app's existing light-mode UI on the fly — no values-night resources needed. It sounds convenient, but the results are often imprecise: the system is guessing at which colors to invert or darken, and it can produce washed-out cards, oddly-inverted images, or poor contrast in places you never explicitly designed for dark mode.

Light vs. Dark Resource Resolution

Troubleshooting