Php 如何使用可选参数创建构造函数？

我有_构造（$parameter）

现在我想要一个没有如下参数的默认构造函数：

public function __construct() {

    $this->id = NULL;
    $this->nick = NULL;
    $this->email = NULL;
    $this->password = NULL;
    $this->birthDay = NULL;
    $this->sex = NULL;
    $this->about = NULL;
    $this->city = NULL;
    $this->photo = NULL;
    $this->following = NULL;
    $this->followers = NULL;
    $this->statu = NULL; 

}

Fatal error: Cannot redeclare User::__construct() in /Applications/MAMP/htdocs/xxx/Application/User.php on line 33

但有些地方出了问题，我得到了如下错误：

public function __construct() {

    $this->id = NULL;
    $this->nick = NULL;
    $this->email = NULL;
    $this->password = NULL;
    $this->birthDay = NULL;
    $this->sex = NULL;
    $this->about = NULL;
    $this->city = NULL;
    $this->photo = NULL;
    $this->following = NULL;
    $this->followers = NULL;
    $this->statu = NULL; 

}

Fatal error: Cannot redeclare User::__construct() in /Applications/MAMP/htdocs/xxx/Application/User.php on line 33

我怎么能同时有两个带参数和不带参数的构造函数

PHP中没有重载；不能有名称相同但参数不同的方法

因为您的所有属性都默认为null，所以没有理由自己这么做。我建议采取以下措施：

public function __construct($nick = null) {
    if ($nick != null) {
        $query = "SELECT * FROM Users WHERE nick='".$nick."'";
        $result = App::runQuery($query);
        $user = $result->fetch_object();

        $this->id = $user->id;
        $this->nick = $user->nick;
        $this->email = $user->email;
        $this->password = $user->password;
        $this->birthDay = $user->birthDay;
        $this->sex = $user->sex;
        $this->about = $user->about;
        $this->city = $user->city;
        $this->photo = $user->photo;
        $this->following = $user->following;
        $this->followers = $user->followers;
        $this->statu = $user->statu; 
    }
}

上述代码的另一种选择是使用多个静态构造函数方法，并使用私有构造函数：

private function __construct() {
}

public static function createFromNick($nick) {
    $self = new self();

    $query = "SELECT * FROM Users WHERE nick='".$nick."'";
    $result = App::runQuery($query);
    $user = $result->fetch_object();

    $self->id = $user->id;
    $self->nick = $user->nick;
    $self->email = $user->email;
    $self->password = $user->password;
    $self->birthDay = $user->birthDay;
    $self->sex = $user->sex;
    $self->about = $user->about;
    $self->city = $user->city;
    $self->photo = $user->photo;
    $self->following = $user->following;
    $self->followers = $user->followers;
    $self->statu = $user->statu;

    return $self;
}

public static function createEmpty() {
    return new self();
}

---

有关详细信息，请查看此答案：

非常感谢您的回答。我用我的方法解决了这个问题

public function __construct($nick) {
    if($nick != NULL) {//for user 
        $query = "SELECT * FROM Users WHERE nick='".$nick."'";
        $result = App::runQuery($query);
        $user = $result->fetch_object();

        $this->id = $user->id;
        $this->nick = $user->nick;
        $this->email = $user->email;
        $this->password = $user->password;
        $this->birthDay = $user->birthDay;
        $this->sex = $user->sex;
        $this->about = $user->about;
        $this->city = $user->city;
        $this->photo = $user->photo;
        $this->following = $user->following;
        $this->followers = $user->followers;
        $this->statu = $user->statu; 
    }else {//for null
        $this->id = NULL;
        $this->nick = NULL;
        $this->email = NULL;
        $this->password = NULL;
        $this->birthDay = NULL;
        $this->sex = NULL;
        $this->about = NULL;
        $this->city = NULL;
        $this->photo = NULL;
        $this->following = NULL;
        $this->followers = NULL;
        $this->statu = NULL;
    }

}

---

它起作用了

虽然两年后你可能还没有开始研究这个问题，但这段代码中有一个明显的SQL注入错误。我认为这不是一个好的实现。我认为你错过了@TimCooper提出的可选的实际论点，这里是线索

public function\u构造（$nick=null）

注意，在PHP中，构造函数不允许抛出任何

可丢弃的

s，例如

异常

s。它只会使PHP脚本的执行崩溃。通常PHP中的数据库查询允许抛出

异常

s。但我不确定在这种情况下这个App：：东西是什么。