Android SystemUI 侧滑屏幕实现返回功能

【相关文件】
frameworks/base/services/core/java/com/android/server/wm/DisplayPolicy.java
frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager

【实现】
frameworks/base/services/core/java/com/android/server/wm/DisplayPolicy.java

这里我们要动态来开关控制这个功能，所以我们需要申请一个Boolean 类型 的flag 变量作为标识。

    //wangrui Whether to enable the sliding back function
    public static boolean flag = true;

侧滑返回其实就跟我们点击了一下back键是同一个意思，那么我们只需要在用户侧滑时，模拟一下back 键被按下就可以实现这个功能！这里我们先自己写好模拟虚拟按键的方法

//wangrui Simulate back button
    private void sendKeyCode(final int keyCode) {
        if (flag){
            new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        // 创建一个Instrumentation对象
                        Instrumentation inst = new Instrumentation();
                        // 调用inst对象的按键模拟方法
                        inst.sendKeyDownUpSync(keyCode);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }).start();
        }
    }

右滑时会回调到 onSwipeFromRight()，左滑时会回调到 onSwipeFromLeft，所以我们只需要在用户每次侧滑时，发送一次模拟back按键就可实现这个效果

DisplayPolicy(WindowManagerService service, DisplayContent displayContent) {
        mService = service;
        mSystemGestures = new SystemGesturesPointerEventListener(mContext, mHandler,
                new SystemGesturesPointerEventListener.Callbacks() {
                    @Override
                    public void onSwipeFromTop() {
                        if (mStatusBar != null) {
                            requestTransientBars(mStatusBar);
                        }
                    }

                    @Override
                    public void onSwipeFromBottom() {
                        if (mNavigationBar != null && mNavigationBarPosition == NAV_BAR_BOTTOM) {
                            requestTransientBars(mNavigationBar);
                        }
                    }

                    @Override
                    public void onSwipeFromRight() {
+                       //wangrui Simulate back button
+                        sendKeyCode(4);
                        final Region excludedRegion = Region.obtain();
                        synchronized (mLock) {
                            mDisplayContent.calculateSystemGestureExclusion(
                                    excludedRegion, null );
                        }
                        final boolean sideAllowed = mNavigationBarAlwaysShowOnSideGesture
                                || mNavigationBarPosition == NAV_BAR_RIGHT;
                        if (mNavigationBar != null && sideAllowed
                                && !mSystemGestures.currentGestureStartedInRegion(excludedRegion)) {
                            requestTransientBars(mNavigationBar);
                        }
                        excludedRegion.recycle();
                    }

                    @Override
                    public void onSwipeFromLeft() {
+                        //wangrui Simulate back button
+                        sendKeyCode(4);
                        final Region excludedRegion = Region.obtain();
                        synchronized (mLock) {
                            mDisplayContent.calculateSystemGestureExclusion(
                                    excludedRegion, null );
                        }
                        final boolean sideAllowed = mNavigationBarAlwaysShowOnSideGesture
                                || mNavigationBarPosition == NAV_BAR_LEFT;
                        if (mNavigationBar != null && sideAllowed
                                && !mSystemGestures.currentGestureStartedInRegion(excludedRegion)) {
                            requestTransientBars(mNavigationBar);
                        }
                        excludedRegion.recycle();
                    }

                    @Override
                    public void onFling(int duration) {
                        if (mService.mPowerManagerInternal != null) {
                            mService.mPowerManagerInternal.powerHint(
                                    PowerHint.INTERACTION, duration);
                        }
                    }
    }

难度增加
以上步骤虽然已经实现了侧滑返回功能，不过如果想要自由控制禁用启用侧滑功能，可以这么做：
frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager

注册一个广播，目的是为了让系统能够接收到用户想开启还是禁用的消息

@Override
    public void init(Context context, IWindowManager windowManager,
            WindowManagerFuncs windowManagerFuncs) {
+    // wangrui register for whether to enable the sliding back functiont broadcasts
+        filter = new IntentFilter("com.xxx.my.back");
+        context.registerReceiver(myBackReceiver, filter);
}

然后在你的APP或者系统上只需要发出这么一条广播，就可以实现这个功能啦！这里面的逻辑很简单，就是在你每一次发出广播，就会改变是否禁启用侧滑功能标识的状态 flag！是不是跟我们前面设置的 flag 产生联系啦！

    //wangrui Change sideslip status
    BroadcastReceiver myBackReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            DisplayPolicy.flag = (!DisplayPolicy.flag);
        }
    };

好啦，我叫王睿丶，如果您有Android开发的难题可以咨询我，Q：1787424177，谢谢您的来访，感谢支持！