android P 添加自定义系统属性，并监听变化

在系统中设置添加一个控制扫码使能开关，在其他地方可以获取这个值，并根据这个值做相关处理。

1.添加自定义属性变量名

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

 public static final class System extends NameValueTable {        ...    1. 添加变量名称        /**     *  add by wxd for qrscan     */    public static final String QRSCAN_MODE = "qrscan_mode";      private static final Validator QRSCAN_MODE_VALIDATOR = BOOLEAN_VALIDATOR;   // 不加这个编译不过    ...   2. SETTINGS_TO_BACKUP中添加    public static final String[] SETTINGS_TO_BACKUP = {        QRSCAN_MODE,        STAY_ON_WHILE_PLUGGED_IN,   // moved to global        ...               3. PUBLIC_SETTINGS中添加    public static final Set<String> PUBLIC_SETTINGS = new ArraySet<>();        static {              PUBLIC_SETTINGS.add(QRSCAN_MODE);           PUBLIC_SETTINGS.add(END_BUTTON_BEHAVIOR);               ...          4. VALIDATORS中添加         public static final Map<String, Validator> VALIDATORS = new ArrayMap<>();        static {           VALIDATORS.put(QRSCAN_MODE, QRSCAN_MODE_VALIDATOR);           ...

2.添加新文件QrScanPreferenceController，改变值并发出通知

添加： vendor/mediatek/proprietary/packages/apps/MtkSettings/src/com/android/settings/security/QrScanPreferenceController.java

 package com.android.settings.security; import android.content.Context; import android.os.UserHandle; import android.provider.Settings; import com.android.internal.widget.LockPatternUtils; import com.android.settings.core.TogglePreferenceController; import com.android.settings.overlay.FeatureFactory; import com.android.settings.R;  public class QrScanPreferenceController extends TogglePreferenceController {     private Context mContext;     private static final String KEY_QRSCAN_SETTING = "qrscan_setting";     private static final String QRSCAN_SETTING_ENABLE = "key_qrscan_setting";     private int QRSCAN_ON = 1;  // 打开     private int QRSCAN_OFF = 0; // 关闭     public QrScanPreferenceController(Context context) {         super(context, KEY_QRSCAN_SETTING);                 mContext = context;     }     @Override     public boolean isChecked() {         return Settings.System.getInt(mContext.getContentResolver(),                 Settings.System.QRSCAN_MODE, QRSCAN_ON ) != QRSCAN_ON ;     }     @Override     public boolean setChecked(boolean isChecked) {         Settings.System.putInt(mContext.getContentResolver(), Settings.System.QRSCAN_MODE,                 isChecked ? QRSCAN_ON : QRSCAN_ON );                 mContext.getContentResolver().notifyChange(Settings.System.getUriFor(                     Settings.System.QRSCAN_MODE),null);  // 发出通知QRSCAN_MODE的值发生变化         return true;     }     @Override     public int getAvailabilityStatus() {         return AVAILABLE; // 其他值不会显示     } }

3.加入到Setting的布局中

添加： /vendor/mediatek/proprietary/packages/apps/MtkSettings/res/xml/security_dashboard_settings.xml

 <SwitchPreference       android:key="qrscan_setting"       android:title="@string/qrscan_setting"       android:summary="@string/qrscan_setting_summery"       settings:controller="com.android.settings.security.QrScanPreferenceController"/>

添加： /vendor/mediatek/proprietary/packages/apps/MtkSettings/src/com/android/settings/security/SecuritySettings.java

 private static List<AbstractPreferenceController> buildPreferenceControllers(Context context,      Lifecycle lifecycle, SecuritySettings host) {      ...     controllers.add(new QrScanPreferenceController(context));     return controllers; }

3.注册ContentObserver，值发生变化时得到通知

添加： /frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager.java

 class SettingsObserver extends ContentObserver {    SettingsObserver(Handler handler) {        super(handler);    }    void observe() {      // Observe all users' changes      ContentResolver resolver = mContext.getContentResolver();          ...      resolver.registerContentObserver(Settings.System.getUriFor(           Settings.System.QRSCAN_MODE), false, this,           UserHandle.USER_ALL);           // add by wxd           updateSettings();    }             @Override     public void onChange(boolean selfChange) {   // 值发生变化                int qrscanMode = Settings.System.getInt(mContext.getContentResolver(),Settings.System.QRSCAN_MODE, 1);    }}

1.添加自定义属性变量名

2.添加新文件QrScanPreferenceController，改变值并发出通知

3.加入到Setting的布局中

3.注册ContentObserver，值发生变化时得到通知

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