PROBLEM

You have a GCM class which includes a send_notification function. In a different class, Demand.php, we trying to use the send_notification function.

So we have a constructor in Demand.php which points to  GCM class:

$gcm = new GCM(); 

This $gcm variable is used in a function inside that class :

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

That’s where we get the error:

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

Inside our function it worked correctly. But is there no other way of doing this? That means should it not be alright only by creating $gcm in the constructor of Demand.php?

SOLUTION 1

Happens with code similar to xyz->method() where xyz is not an object and therefore that method can not be called.

This is a fatal error which will stop the script (forward compatibility notice: It will become a catchable error starting with PHP 7).

Most often this is a sign that the code has missing checks for error conditions. Validate that an object is actually an object before calling its methods.

Example:

// ... some code using PDO
$statement = $pdo->prepare('invalid query', ...); $statement->execute(...); 

In the example above, the query cannot be prepared and prepare() will assign false to $statement.
Trying to call the execute() method will then result in the Fatal Error because false is a “non-object” because the value is a boolean.

Figure out why your function returned a boolean instead of an object. For example, check the $pdo object for the last error that occurred.
Details on how to debug this will depend on how errors are handled for the particular function/object/class.

If even the ->prepare is failing then your $pdo database handle object didn’t get passed into the current scope.
Find where it got defined. Then pass it as a parameter, store it as property, or share it via the global scope.

SOLUTION 2

If we place $gcm = new GCM(); in the constructor of our Demand class, then the variable $gcm will only be available in the constructor method.

If we want to be able to access the $gcm variable throughout the Demand class we will need to set it as a property of the class like so:

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); ... }
 ... } 

SOLUTION 3
gcm will only be available in the scope of the constructor unless you initialize it as a instance variable.

class Demand 
{
 private $_gcm; function __construct() 
{ 
$this->_gcm = new GCM(); 
} 
function youWantToUseGcmIn()
 {
 $this->_gcm->send_notification(.....);
 // access it like this
 } 
} 

SOLUTION 4

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