查看应用悬浮窗是否开启的方法（针对MIUI, EMUI）

    /**
     * 判断悬浮窗权限
     *
     * @param context 上下文
     */
    public static boolean isFloatWindowOpAllowed(Context context) {
        final int version = Build.VERSION.SDK_INT;

        if (version >= 19) {
            return checkOp(context, 24);//24表示悬浮窗权限在AppOpsManager中
        } else {
            //0x8000000表示1000000000000000000000000000如果&第28位所得值为1则该位置被置为1，悬浮窗打开
            return (context.getApplicationInfo().flags & 0x8000000) == 1<<27;
        }
    }
    
    protected static boolean checkOp(Context context, int op) {
        final int version = Build.VERSION.SDK_INT;
        if (version >= 19) {
            AppOpsManager manager = (AppOpsManager) context.getSystemService("appops");
            try {
                Object object = invokeMethod(manager, "checkOp", op, Binder.getCallingUid(), getPackageName(context));
                return AppOpsManager.MODE_ALLOWED == (Integer) object;
            } catch (Exception e) {
                LogTool.e("CheckMIUI", e.toString());
            }
        } else {
            LogTool.e("CheckMIUI", "Below API 19 cannot invoke!");
        }
        return false;
    }

    public static String getPackageName(Context context) throws PackageManager.NameNotFoundException {
        PackageInfo pInfo = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);
        return pInfo.packageName;
    }
    
    public static Object invokeMethod(AppOpsManager manager, String method, int op, int uid, String packageName){
        Class c = manager.getClass();
        try {
            Class[] classes = new Class[] {int.class, int.class, String.class};
            Object[] x2 = {op, uid, packageName};
            Method m = c.getDeclaredMethod(method, classes);
            return m.invoke(manager, x2);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return -1;
    }