即使在对utf8mb4进行更改后，JSON仍显示NULL - 我错过了什么？

Question

本质上，我的JSON为包含特殊字符的字段打印NULL。

我已经阅读过该主题，并按照重复的问题以及其他主题，特别强调了一个帖子，我需要执行以下操作：

If you're using mysqli, you can call set_charset(): $mysqli->set_charset('utf8mb4'); // object oriented style mysqli_set_charset($link, 'utf8mb4'); // procedural style If you're stuck with plain mysql but happen to be running PHP ≥ 5.2.3, you can call mysql_set_charset. If the driver does not provide its own mechanism for setting the connection character set, you may have to issue a query to tell MySQL how your application expects data on the connection to be encoded: SET NAMES 'utf8mb4'.

我已按照openConnection()函数中的说明完成此操作，如下面的连接脚本中所示：

<?php

ini_set('display_errors', 1); 
ini_set('log_errors',1); 
error_reporting(E_ALL); 
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

class MySQLDao{

var $dbhost = null;
var $dbuser = null;
var $dbpass = null;
var $conn = null;
var $dbname = null;
var $result = null;

public function __construct(){
    $this->dbhost = Conn::$dbhost;
    $this->dbuser = Conn::$dbuser;
    $this->dbpass = Conn::$dbpass;
    $this->dbname = Conn::$dbname;
}

public function openConnection()
{

    $this->conn = new mysqli($this->dbhost, $this->dbuser, $this->dbpass, $this->dbname);
    if (mysqli_connect_errno())
        echo new Exception("Could not establish connection with database");
mysqli_set_charset($this->conn, "utf8mb4");
}

我在phpMyAdmin中浏览了我的数据库，并将所有归类转换为ut8mb4_bin。我按照建议添加了mysql_set_chars行，并且我还通过这种类型的命令将所有表格更改为utf8mb4 ALTER TABLE teams CHANGE name name VARCHAR(191) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

这些是来自phpMyAdmin的数据库设置：

  

我的网络服务器详情是   阿帕奇   数据库客户端版本：libmysql - 5.0.77   PHP扩展：mysqli文档   PHP版本：5.3.3

然而，这一切都没有解决我的问题。

我的character_set_server显示为latin1，这可能是问题吗？

+--------------------------+--------------------+ | Variable_name | Value | +--------------------------+--------------------+ | character_set_client | utf8mb4 | | character_set_connection | utf8mb4 | | character_set_database | utf8mb4 | | character_set_filesystem | binary | | character_set_results | utf8mb4 | | character_set_server | latin1 | | character_set_system | utf8 | | collation_connection | utf8mb4_unicode_ci | | collation_database | utf8mb4_unicode_ci | | collation_server | latin1_swedish_ci | +--------------------------+--------------------+

我不知道还有什么可尝试的。