先说一句：MIUI请放弃治疗！这里给个传送门：
MIUI通知类短信权限的坑
识别短信验证码并提取还是挺常见的一个需求。所要解决的问题主要有：
1、如何监听
2、如何提取短信中的验证码
3、监听多次调用问题
直接看下面代码吧，很明了。需要注意的点有就是onChange会多次调用。其实打Log就看的出了，收到一条短信会调用两次onChange，Log结果如下：

mUri===content://sms/raw/20
mUri===content://sms/inbox/20

安卓7.0以上系统，点击标记为已读，也会调用一次

mUri===content://sms

收到一条短信都是uri后面都会有确定的一个数字，对应数据库的_id，比如上面的20

public static class SMSCodeObserver extends ContentObserver {
        private Activity mActivity;
        private static final String TAG = "SMSCodeObserver";
        private SMSCodeListener mSMSCodeListener;
        private Uri mUri;

        public void setSMSCodeListener(SMSCodeListener SMSCodeListener) {
            mSMSCodeListener = SMSCodeListener;
        }

        public interface SMSCodeListener {
            void onResult(String code);
        }

        public SMSCodeObserver(Handler handler, Activity activity) {
            super(handler);
            mActivity = activity;
        }


        public void register() {
            mActivity.getContentResolver().registerContentObserver(
                    Uri.parse("content://sms/"), true, this);
        }

        public void unRegister() {
            mActivity.getContentResolver().unregisterContentObserver(this);
        }

        @Override
        public void onChange(boolean selfChange, Uri uri) {
            super.onChange(selfChange, uri);
            if (uri == null) {
                mUri = Uri.parse("content://sms/inbox");
            } else {
                mUri = uri;
            }
            if (mUri.toString().contains("content://sms/raw") || mUri.toString().equals("content://sms")) {
                return;
            }
            LogUtils.d(TAG, "mUri===" + mUri.toString());
            AndPermission.with(mActivity)
                    .permission(Manifest.permission.READ_SMS)
                    .requestCode(100)
                    .callback(this)
                    .rationale(new RationaleListener() {
                        @Override
                        public void showRequestPermissionRationale(int requestCode, Rationale rationale) {
                            AndPermission.rationaleDialog(mActivity, rationale)
                                    .show();
                        }
                    })
                    .start();
        }

        @PermissionYes(100)
        @SuppressWarnings("unused")
        private void getPermissionYes(List<String> grantedPermissions) {
            handleSMS();
        }

        @PermissionNo(100)
        @SuppressWarnings("unused")
        private void getPermissionNo(List<String> deniedPermissions) {
            if (AndPermission.hasPermission(mActivity, Manifest.permission.READ_SMS)) {
                handleSMS();
            } else {
                AndPermission.defaultSettingDialog(mActivity)
                        .show();
            }
        }

        private void handleSMS() {

             /* 按照日期倒序排序 */
            Cursor cursor = mActivity.getContentResolver().query(mUri, null, null, null, "date desc");
            if (cursor != null) {
                if (cursor.moveToFirst()) {//游标移动到first位置
                    /* 发件人的号码 */
                    String address = cursor.getString(cursor.getColumnIndex("address"));
                    /* 短信内容 */
                    String body = cursor.getString(cursor.getColumnIndex("body"));
                    LogUtils.d(TAG, "address:" + address + ",body:" + body);
                    if (!body.contains("验证码")) {
                        return;
                    }

                    /* 利用正则提取验证码（根据实际情况修改） */
                    String code = getSMSCode(body);
                    if (code != null) {
                        if (mSMSCodeListener != null) {
                            mSMSCodeListener.onResult(code);
                        }
                        LogUtils.d(TAG, "code:" + code);
                    }
                }
                cursor.close();
            }
        }

        private static String getSMSCode(String msg) {
            /*提取正则表达式，需按需修改*/
            Pattern p = Pattern.compile("(?<![0-9])([0-9]{6})(?![0-9])");
            Matcher m = p.matcher(msg);
            if (m.find()) {
                LogUtils.d(TAG, m.group());
                return m.group(0);
            }
            return null;
        }
    }