php 致命错误.. 调用成员函数.. 在非对象上

Fatal error.. Call to a member function.. on a non-object

提问by user1732457

I have a GCMclass which includes a send_notification function. In a different class, Demand.php, I am trying to use the send_notification function. So I have a constructor in Demand.phpwhich points to my GCMclass like this:

我有一个GCM包含 send_notification 函数的类。在另一个类中Demand.php，我尝试使用 send_notification 函数。所以我有一个构造函数，Demand.php它GCM像这样指向我的类：

 $gcm = new GCM();

This $gcmvariable is used in a function inside that class like this:

该$gcm变量在该类中的函数中使用，如下所示：

$result = $gcm->send_notification($registatoin_ids, $message);

That's where I get the error:

这就是我收到错误的地方：

<br />n<b>Fatal error</b>:  Call to a member function send_notification() on a non-object in..

I searched for the problem and found out that the problem is that $gcmis null and that's why it's calling nothing. So when I put the

我搜索了这个问题，发现问题$gcm是 null ，这就是为什么它什么都不调用。所以当我把

$gcm = new GCM();

Inside my function it worked correctly. But is there no other way of doing this? I mean should it not be alright only by putting creating $gcmin the constructor of Demand.php?

在我的函数中，它工作正常。但是没有其他方法可以做到这一点吗？我的意思是如果它不把创建没事仅$gcm在构造函数Demand.php？

Here are the parts where I am referring to:

以下是我所指的部分：

function __construct() {
    require_once 'GCM.php';
    require_once 'DB_Connect.php';
    require_once 'DB_Functions.php';
    // connecting to database
    $this->db = new DB_Connect();
    $this->db->connect();
    $gcm = new GCM();
    $df = new DB_Functions();

}

// destructor
function __destruct() {

}


public function getDistance($uuid, $name, $distance, $latstart, $lonstart, $latend, $lonend, $gcm_regId) {
    $user_new = array ("$uuid", "$name", "$distance","$latstart", "$lonstart", "$latend", "$lonend","$gcm_regId");  
    $query = sprintf("SELECT uid, distance,latstart, lonstart, latend, lonend, gcm_regid, name FROM user_demand WHERE latstart='%s' AND lonstart='%s'",
    mysql_real_escape_string($latstart),
    mysql_real_escape_string($lonstart));
    $user = mysql_query($query);

    $no_of_rows = mysql_num_rows($user);

    while($user_old = mysql_fetch_assoc($user))
    {
        $djson = $this->findDistance($latend,$lonend,$user_old["latend"],$user_old["lonend"] );

        if ($user_old["distance"]+$distance>=$djson) {
            $match = mysql_query("INSERT INTO matched_users(gcm_a, gcm_b, name_a, name_b) VALUES(".$user_old['gcm_regid'].",".$user_new['gcm_regId'].",".$user_old['name'].",".$user_new['name'].")");
            $registatoin_ids = array($gcm_regId);
            $message = array("var" => $name);
            $result = $gcm->send_notification($registatoin_ids, $message);
        }
    }
}

回答by Stu

If you put $gcm = new GCM();in the constructor of your Demand class, then the variable $gcmwill only be available in the constructor method.

如果您放入$gcm = new GCM();Demand 类的构造函数，则该变量$gcm将仅在构造函数方法中可用。

If you want to be able to access the $gcmvariable throughout the Demand class you'll need to set it as a property of the class like so:

如果您希望能够在$gcm整个 Demand 类中访问变量，您需要将其设置为类的属性，如下所示：

class Demand()
{
    /**
     * Declare the variable as a property of the class here
     */
    public $gcm;

    ...
    function __construct()
    {
        ...
        $this->gcm = new GCM();
        ...
    }

    function myFunction()
    {
        ...
        // You can access the GCM class now in any other method in Demand class like so:
        $result = $this->gcm->send_notification($registatoin_ids, $message);
        ...
    }
    ...
}

回答by aziz punjani

gcm will only be available in the scope of the constructor unless you initialize it as a instance variable.

gcm 将仅在构造函数的范围内可用，除非您将其初始化为实例变量。

class Demand
{
    private $_gcm; 
    function __construct() 
    {
        $this->_gcm = new GCM(); 
    }

    function youWantToUseGcmIn()
    {
        $this->_gcm->send_notification(.....); // access it like this 
    }
}

回答by Marc B

You create $gcm in an object constructor, then use it from some other method in the same class? You're not storing it properly, then. You have to do:

您在对象构造函数中创建 $gcm，然后从同一类中的其他方法中使用它？那么你没有正确存储它。你必须要做：

class X {
    function constructor() {
        $this->gcm = new GCM();
    }

    function other_method() {
        $this->gcm->send_notification(...);
    }
}

if you have

如果你有

function constructor() {
    $gcm = new GCM();  <-- this is just a temporary local variable.
}

all you're doing is creating a local variable within the constructor, which will be destroyed as soon as the constructor returns. Saving the new object in $this->gcm saves it inside the containing object and makes it available to other methods.

你所做的就是在构造函数中创建一个局部变量，一旦构造函数返回，它就会被销毁。在 $this->gcm 中保存新对象会将其保存在包含对象中，并使其可用于其他方法。

回答by Techie

This means $gcmis not an object, probably it's NULL or false in some cases (nothing found) due to it's not accessible. Out of scope

这意味着$gcm它不是一个对象，在某些情况下它可能是 NULL 或 false（没有找到），因为它不可访问。超出范围