在 setContentView(R.layout.activity_main);
之后调用
setFullscreen();

 private void setFullscreen() {
        try {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
                getWindow().setDecorFitsSystemWindows(false);
                WindowInsetsController controller = getWindow().getInsetsController();
                if (null != controller) {
                    controller.hide(WindowInsets.Type.statusBars() | WindowInsets.Type.navigationBars());
                    controller.setSystemBarsBehavior(WindowInsetsController.BEHAVIOR_SHOW_TRANSIENT_BARS_BY_SWIPE);
                }
                return;
            }
        } catch (Exception e) {
            Log.e(TAG, e.toString(), e);
        }

        try {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
                getWindow().getAttributes().layoutInDisplayCutoutMode = WindowManager.LayoutParams.LAYOUT_IN_DISPLAY_CUTOUT_MODE_SHORT_EDGES;
                return;
            }
        } catch (Exception e) {
            Log.e(TAG, e.toString(), e);
        }

        try {
            getWindow().getDecorView().setSystemUiVisibility(
                    View.SYSTEM_UI_FLAG_FULLSCREEN
                            | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
                            | View.SYSTEM_UI_FLAG_IMMERSIVE
                            | View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                            | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                            | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                            | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY
            );
        } catch (Exception e) {
            Log.e(TAG, e.toString(), e);
        }
    }