1、问题来源

由于我是做平板方案的，前段时间遇到一个问题，说的是第三方App进入全屏模式时，底部导航栏会遮挡住App下方的内容，当时的想法是为什么有的App进入全屏模式会自动留出导航栏的位置，并且将自己底部操作栏顶上去，这样子就能既触发App底部操作栏事件，又能操作底部导航栏；而有的App的底部操作栏则直接被导航栏覆盖。我能否读取当前App是否进入全屏从而修改导航栏的位置，动手过后发现很复杂，而且难以适配。后面换了一个想法，就在设置App中直接让用户手动进行设置，控制导航栏是否显示或者隐藏，也可以理解为三指导航以及虚拟按键导航的相互切换。

2、问题解析

由于产品是自带了自己研发的设置App，所以主要讲一下Framework层的修改，而不涉及设置App方面的修改。

2-1 显示与隐藏的接口开发

在之前的文章中，我修改过导航栏的状态，涉及沉浸式导航栏与导航栏延迟消失，知道导航栏的创建在packages/apps/SystemUI/src/com/android/systemui/statusbar/phone/StatusBar.java

java

复制代码

protected void createNavigationBar() {
    mNavigationBarView = NavigationBarFragment.create(mContext, (tag, fragment) -> {
        mNavigationBar = (NavigationBarFragment) fragment;
        if (mLightBarController != null) {
            mNavigationBar.setLightBarController(mLightBarController);
        }
        mNavigationBar.setCurrentSysuiVisibility(mSystemUiVisibility);
    });
}

如果我们想要显示与隐藏导航栏的话，可以再此处添加接口；

显示的话，很好理解，就是上述的createNavigationBar()

java

复制代码

/**
 * Controls the display of navigation bar.
 *
 * @Author wayhoi
 * @Date 2022-03-13 16:43
 */
private void displayOfNavigationBar() {
    createNavigationBar();
}

隐藏的话，可以通过packages/apps/SystemUI/src/com/android/systemui/statusbar/phone/StatusBar.java中的destroy()中查阅到

java

复制代码

public void destroy() {
    // Begin old BaseStatusBar.destroy().
    mContext.unregisterReceiver(mBannerActionBroadcastReceiver);
    mLockscreenUserManager.destroy();
    try {
        mNotificationListener.unregisterAsSystemService();
    } catch (RemoteException e) {
        // Ignore.
    }
    mEntryManager.destroy();
    // End old BaseStatusBar.destroy().
    if (mStatusBarWindow != null) {
        mWindowManager.removeViewImmediate(mStatusBarWindow);
        mStatusBarWindow = null;
    }
    if (mNavigationBarView != null) {
        mWindowManager.removeViewImmediate(mNavigationBarView);
        mNavigationBarView = null;
    }
    mContext.unregisterReceiver(mBroadcastReceiver);
    mContext.unregisterReceiver(mDemoReceiver);
    mAssistManager.destroy();

    if (mQSPanel != null && mQSPanel.getHost() != null) {
        mQSPanel.getHost().destroy();
    }
    Dependency.get(ActivityStarterDelegate.class).setActivityStarterImpl(null);
    mDeviceProvisionedController.removeCallback(mUserSetupObserver);
    Dependency.get(ConfigurationController.class).removeCallback(this);
    mZenController.removeCallback(this);
    mAppOpsListener.destroy();
}

通过阅读代码，可以发现，隐藏(这里用去除来描述会更恰当)的方法如下：

java

复制代码

/**
 * Controls the hiding of navigation bar.
 *
 * @Author wayhoi
 * @Date 2022-03-13 17:12
 */
private void hidingOfNavigationBar() {
    if (mWindowManager != null && mNavigationBarView != null) {
        mWindowManager.removeViewImmediate(mNavigationBarView);
        mNavigationBarView = null;
    }
}

于是，从源码中，我们就将NavigationBar的显示与隐藏接口写好了，接下来就是考虑调用。

2-2 触发接口

这里我用的是通过广播来进行触发，设置应用内通过开关按钮来进行发送显示与关闭的广播。

com/example/settings/operation/BarOperation.java

java

复制代码

/**
 * Action to display of navigation bar.
 */
public static final String ACTION_DISPLAY_OF_NAVIGATION_BAR = "com.example.display_of_navigation_bar";

/**
 * Action to hiding of navigation bar.
 */
public static final String ACTION_HIDING_OF_NAVIGATION_BAR = "com.example.hiding_of_navigation_bar";

/**
 * Intent to display of navigation bar.
 */
private final Intent INTENT_DISPLAY_OF_NAVIGATION_BAR = new Intent(ACTION_DISPLAY_OF_NAVIGATION_BAR);

/**
 * Action to hiding of navigation bar.
 */
private final Intent INTENT_HIDING_OF_NAVIGATION_BAR = new Intent(ACTION_HIDING_OF_NAVIGATION_BAR);



/**
 * Controls the hiding of navigation bar.
 *
 * @Author wayhoi
 * @Date 2022-03-13 17:18
 */
public void switchNavigationBar(boolean isChecked) {
    context.sendBroadcast(isChecked ? INTENT_DISPLAY_OF_NAVIGATION_BAR : INTENT_HIDING_OF_NAVIGATION_BAR);
}

同时让packages/apps/SystemUI/src/com/android/systemui/statusbar/phone/StatusBar.java接收广播：

java

复制代码

+ /**
+  * Action to display of navigation bar.
+  */
+  public static final String ACTION_DISPLAY_OF_NAVIGATION_BAR = "com.example.display_of_navigation_bar";
+  
+ /**
+  * Action to hiding of navigation bar.
+  */
+  public static final String ACTION_HIDING_OF_NAVIGATION_BAR = "com.example.hiding_of_navigation_bar";


protected void makeStatusBarView() {
    //省略代码
    // receive broadcasts
    IntentFilter filter = new IntentFilter();
    filter.addAction(Intent.ACTION_CLOSE_SYSTEM_DIALOGS);
    filter.addAction(Intent.ACTION_SCREEN_OFF);
    filter.addAction(DevicePolicyManager.ACTION_SHOW_DEVICE_MONITORING_DIALOG);
+   filter.addAction(ACTION_NAVIGATION_HIDE);
+   filter.addAction(ACTION_NAVIGATION_SHOW);
    //省略代码
}

private final BroadcastReceiver mBroadcastReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            //省略代码
+            else if (ACTION_NAVIGATION_HIDE.equals(action)) {
+                hidingOfNavigationBar();
+            } else if (ACTION_NAVIGATION_SHOW.equals(action)) {
+                displayOfNavigationBar();
            }
        }
};

到这里，我们就已经写完了；编译、刷机、测试，发现切换设置中的开关时，已经有效地可以控制导航栏的显示与隐藏；

但是有个问题，当我隐藏导航栏后，重新开机，发现导航栏又会出现，说明当前的代码无法记录导航栏的状态。于是我想到，可以用数据库来记录状态。

2-3 状态持久化

我们继续编写，修改frameworks/base/core/java/android/provider/Settings.java

java

复制代码

public final class Settings {
    //省略代码
    
    public static final class System extends NameValueTable {
        //省略代码
        
+        /** {@hide} */
+        public static final String HIDING_OF_NAVIGATION_BAR = "hiding_of_navigation_bar";
+        /** {@hide} */
+        public static final Uri HIDING_OF_NAVIGATION_BAR_URI =getUriFor(HIDING_OF_NAVIGATION_BAR);
+        private static final Validator HIDING_OF_NAVIGATION_BAR_VALIDATOR = URI_VALIDATOR;
        
        //省略代码
        public static final String[] SETTINGS_TO_BACKUP = {
+           HIDING_OF_NAVIGATION_BAR
            //省略代码
        }
        
         //省略代码
        public static final Set<String> PUBLIC_SETTINGS = new ArraySet<>();
        static {
+           PUBLIC_SETTINGS.add(HIDING_OF_NAVIGATION_BAR);
            //省略代码
        }
        
        //省略代码
        public static final Map<String, Validator> VALIDATORS = new ArrayMap<>();
        static {
+           VALIDATORS.put(HIDING_OF_NAVIGATION_BAR, HIDING_OF_NAVIGATION_BAR_VALIDATOR);
            //省略代码
        } 
     
        //省略代码
    }
    
    //省略代码
}

然后去frameworks/base/packages/SettingsProvider/src/com/android/providers/settings/DatabaseHelper.java初始化HIDING_OF_NAVIGATION_BAR的初始值，这里我们定义规则：0为隐藏，1为显示

java

复制代码

@Deprecated
class DatabaseHelper extends SQLiteOpenHelper {
    //省略代码
    
    private void loadSystemSettings(SQLiteDatabase db) {
    	SQLiteStatement stmt = null;
        try {
            stmt = db.compileStatement("INSERT OR IGNORE INTO system(name,value)"
                    + " VALUES(?,?);");
+		/// M: modify by wayhoi, init the value of navigation bar state.  @{
+       	loadIntegerSetting(stmt, Settings.System.HIDING_OF_NAVIGATION_BAR, 1);
+           /// @}
            //省略代码
        }
    }
    
    //省略代码
}

往后，我们在调用packages/apps/SystemUI/src/com/android/systemui/statusbar/phone/StatusBar.java中的**displayOfNavigationBar()和hidingOfNavigationBar()**时，便将新值写入数据库，于是我们修改接口：

java

复制代码

protected void makeStatusBarView() {
    //省略代码
    try {
        boolean showNav = mWindowManagerService.hasNavigationBar();
        if (DEBUG) Log.v(TAG, "hasNavigationBar=" + showNav);
        if (showNav) {
            /// M: modify by wayhoi, controls the display and hiding of the navigation bar. 1 is display, and 0 is hiding. @{
            if (1 == Settings.System.getInt(context.getContentResolver(), Settings.System.HIDING_OF_NAVIGATION_BAR, 0)) {
                createNavigationBar();
            }
            /// @}
        }
    } catch (RemoteException ex) {
        // no window manager? good luck with that
    }
    //省略代码
}


/**
 * Controls the display of navigation bar.
 *
 * @Author wayhoi
 * @Date 2022-03-13 16:43
 */
private void displayOfNavigationBar() {
    createNavigationBar();
+   Settings.System.putInt(context.getContentResolver(), Settings.System.HIDING_OF_NAVIGATION_BAR, 1);
}

/**
 * Controls the hiding of navigation bar.
 *
 * @Author wayhoi
 * @Date 2022-03-13 17:12
 */
private void hidingOfNavigationBar() {
    if (mWindowManager != null && mNavigationBarView != null) {
        mWindowManager.removeViewImmediate(mNavigationBarView);
        mNavigationBarView = null;
+   	Settings.System.putInt(context.getContentResolver(), Settings.System.HIDING_OF_NAVIGATION_BAR, 0);
    }
}

同时我们在设置App中，监听HIDING_OF_NAVIGATION_BAR的变化

java

复制代码

public void onResume() {
    super.onResumer();
+   getContext().getContentResolver().registerContentObserver(
+        Settings.System.getUriFor(Settings.System.HIDING_OF_NAVIGATION_BAR),
+        true,
+        navigationObserver
+   );
}

+   /**
+     * 监听导航栏变化
+     *
+     * @Author wayhoi
+     * @Date 2022-03-13 18:31
+     */
+    private ContentObserver navigationObserver = new ContentObserver(new Handler()) {
+        @Override
+        public void onChange(boolean selfChange) {
+			boolean isDisplay = Settings.System.getInt(context.getContentResolver(), Settings.System.HIDING_OF_NAVIGATION_BAR, 0) == 1;    
+            switchOfNavigationBar.setChecked(isDisplay);
+        }
+    };