Add custom Key value in Settings in Android system

The Settings Provider system settings data table saves the preference settings in the system, and the application can access the corresponding preference settings through the Settings API, mainly three types of settings: Settings.Global, Settings.Secure, and Settings.System.
Settings.Global : Global system settings containing preferences that always apply the same way to all defined users. Applications can read these, but not write to them; like the "Security" settings, these apply to preferences that the user must explicitly modify through the system UI or a dedicated API for these values. Commonly used setting items include Bluetooth switch status, adb switch status, etc.
Settings.Secure : Secure system settings, containing system preferences that apps can read but not write to. These preferences are for preferences that the user must explicitly modify through the system UI or a dedicated API for these values, rather than directly by the application. Commonly used setting items include accessibility, VPN status, etc.
Settings.System : System settings, including miscellaneous system preferences. This table contains simple name/value pairs. There are some convenience methods for accessing individual setting entries. Commonly used setting items include ringtone, brightness, time format, etc.
The following describes the process of customizing a Settings.Global key. The method of customizing Settings.Secure and Settings.System is similar.

Modifications in Settings

Source code path:

frameworks/base/core/java/android/provider/Settings.java

Add the constant value of the custom Key in the internal class, which can be of common types such as String, int, and boolean Settings.Global

 public static final class Global extends NameValueTable {
    
    
        /**
         * @hide
         */
        public static final String CUSTOM_KEY = "your_custom_key";
 }

MOVED_TO_GLOBALAdd the corresponding custom Key to the list :

        @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
        private static final HashSet<String> MOVED_TO_GLOBAL;
        @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
        private static final HashSet<String> MOVED_TO_SECURE_THEN_GLOBAL;
        static {
    
    
            MOVED_TO_GLOBAL = new HashSet<>();
            MOVED_TO_SECURE_THEN_GLOBAL = new HashSet<>();

            // these were originally in system but migrated to secure in the past,
            // so are duplicated in the Secure.* namespace
            MOVED_TO_SECURE_THEN_GLOBAL.add(Global.ADB_ENABLED);
            MOVED_TO_SECURE_THEN_GLOBAL.add(Global.BLUETOOTH_ON);
            ...省略
            MOVED_TO_GLOBAL.add(Settings.Global.RADIO_NFC);
            MOVED_TO_GLOBAL.add(Settings.Global.RADIO_CELL);
            MOVED_TO_GLOBAL.add(Settings.Global.RADIO_WIFI);
            MOVED_TO_GLOBAL.add(Settings.Global.RADIO_BLUETOOTH);
            MOVED_TO_GLOBAL.add(Settings.Global.RADIO_WIMAX);
            MOVED_TO_GLOBAL.add(Settings.Global.SHOW_PROCESSES);
            
            /** 添加你的自定义Keys */
            MOVED_TO_GLOBAL.add(Settings.Global.CUSTOM_KEY);

        }

Then add the custom key PUBLIC_SETTINGSto the public system key list:

        /**
         * @hide
         */
        public static final String CUSTOM_KEY = Global.CUSTOM_KEY;

        /**
         * These are all public system settings
         *
         * @hide
         */
        @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
        public static final Set<String> PUBLIC_SETTINGS = new ArraySet<>();
        static {
    
    
            PUBLIC_SETTINGS.add(END_BUTTON_BEHAVIOR);
            PUBLIC_SETTINGS.add(WIFI_USE_STATIC_IP);
            PUBLIC_SETTINGS.add(WIFI_STATIC_IP);
            PUBLIC_SETTINGS.add(WIFI_STATIC_GATEWAY);
            PUBLIC_SETTINGS.add(WIFI_STATIC_NETMASK);
            ...省略
            PUBLIC_SETTINGS.add(HAPTIC_FEEDBACK_ENABLED);
            PUBLIC_SETTINGS.add(SHOW_WEB_SUGGESTIONS);
            PUBLIC_SETTINGS.add(VIBRATE_WHEN_RINGING);
            PUBLIC_SETTINGS.add(APPLY_RAMPING_RINGER);
            
            /** 添加你的自定义Keys*/
            PUBLIC_SETTINGS.add(CUSTOM_KEY);
        }

Modifications in SettingsProvider

1. SettingsProviderAdd it in the system application module 默认值.
Source path:

frameworks/base/packages/SettingsProvider/res/values/defaults.xml

code show as below:

<resources>
    <bool name="def_dim_screen">true</bool>
    <integer name="def_screen_off_timeout">60000</integer>
    <integer name="def_sleep_timeout">-1</integer>
    <bool name="def_airplane_mode_on">false</bool>
    <bool name="def_theater_mode_on">false</bool>
    <!-- Comma-separated list of bluetooth, wifi, and cell. -->
    <string name="def_airplane_mode_radios" translatable="false">cell,bluetooth,wifi,nfc,wimax</string>
    <string name="airplane_mode_toggleable_radios" translatable="false">bluetooth,wifi,nfc</string>
    <string name="def_bluetooth_disabled_profiles" translatable="false">0</string>
    <bool name="def_auto_time">true</bool>
    <bool name="def_auto_time_zone">true</bool>
    <bool name="def_accelerometer_rotation">false</bool>
    <!-- Default screen brightness, from 0 to 255.  102 is 40%. -->
    <integer name="def_screen_brightness">102</integer>
    <bool name="def_screen_brightness_automatic_mode">false</bool>
    <fraction name="def_window_animation_scale">100%</fraction>
    <fraction name="def_window_transition_scale">100%</fraction>
    <bool name="def_haptic_feedback">true</bool>
    ...省略

    <!-- 添加你的自定义Keys -->
    <string name="def_custom_key">key1</bool>

2. By loadGlobalSettingsloading custom Keys into the SettingsProvider system application module 数据库.
Source path:

frameworks/base/packages/SettingsProvider/src/com/android/providers/settings/DatabaseHelper.java

code show as below:

    private void loadGlobalSettings(SQLiteDatabase db) {
    
    
        SQLiteStatement stmt = null;
        final Resources res = mContext.getResources();
        try {
    
    
            stmt = db.compileStatement("INSERT OR IGNORE INTO global(name,value)"
                    + " VALUES(?,?);");

            // --- Previously in 'system'
            loadBooleanSetting(stmt, Settings.Global.AIRPLANE_MODE_ON,
                    R.bool.def_airplane_mode_on);
   
            ...省略
            loadSetting(stmt, Settings.Global.LID_BEHAVIOR, defaultLidBehavior);
            
            //添加你的自定义Keys
            loadStringSetting(stmt, Settings.Global.CUSTOM_KEY, R.string.def_custom_key);
        } finally {
    
    
            if (stmt != null) stmt.close();
        }
    }

    private void loadStringSetting(SQLiteStatement stmt, String key, int resid) {
    
    
        loadSetting(stmt, key, mContext.getResources().getString(resid));
    }

epilogue

After completing the above modifications, you can use the custom Key in any system application:

     String value = Settings.Global.getString(getContentResolver(), Settings.Global.CUSTOM_KEY);

     Settings.Global.putString(getContentResolver(), Settings.Global.CUSTOM_KEY, " ");

For more information, please refer to the related introduction to SettingsProvider in another blog: Talking about data sharing in android system applications