方法一 滑动屏幕 可重新显示出来

protected void hideBottomUIMenu() {
  //隐藏虚拟按键，并且全屏
  if (Build.VERSION.SDK_INT  <=11 && Build.VERSION.SDK_INT < 19) { // lower api
    View v = this.getWindow().getDecorView();
    v.setSystemUiVisibility(View.GONE);
  } else if (Build.VERSION.SDK_INT  >19) {
    //for new api versions.
    View decorView = getWindow().getDecorView();
    int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
        | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY | View.SYSTEM_UI_FLAG_FULLSCREEN;
    decorView.setSystemUiVisibility(uiOptions);
 
  }
}

方法二 滑动也不能重新显示

protected void hideBottomUIMenu() {
  //隐藏虚拟按键，并且全屏
  if (Build.VERSION.SDK_INT  <=11 && Build.VERSION.SDK_INT < 19) { // lower api
    View v = this.getWindow().getDecorView();
    v.setSystemUiVisibility(View.GONE);
  } else if (Build.VERSION.SDK_INT  >= 19) {
    
    Window _window = getWindow();
    WindowManager.LayoutParams params = _window.getAttributes();
    params.systemUiVisibility = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION|View.SYSTEM_UI_FLAG_IMMERSIVE;
    _window.setAttributes(params);
  }
}

隐藏状态栏（让状态栏直接消失，不占位）

  public static void hideStatusBar(Activity activity) {
        if (activity == null) return;
        Window window = activity.getWindow();
        if (window == null) return;
        window.setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);
        window.getDecorView()
                .setSystemUiVisibility(View.SYSTEM_UI_FLAG_FULLSCREEN | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN | View.SYSTEM_UI_FLAG_LAYOUT_STABLE);
        WindowManager.LayoutParams lp = window.getAttributes();
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
            lp.layoutInDisplayCutoutMode = WindowManager.LayoutParams.LAYOUT_IN_DISPLAY_CUTOUT_MODE_SHORT_EDGES;
        }
        window.setAttributes(lp);
    }

如果activity的layout xml根标签设置了以下代码，需要移除，否者内容底部还是会存在预留个底部虚拟按键的padding

android:fitsSystemWindows="true"
 
android:clipToPadding="false"