PHP Fatal error: Using $this when not in object context

In my index.php I'm loading maybe foobarfunc() like this:

 foobar::foobarfunc();  // Wrong, it is not static method

but can also be

$foobar = new foobar;  // correct
$foobar->foobarfunc();

You can not invoke the method this way because it is not a static method.

foobar::foobarfunc();

You should instead use:

$foobar->foobarfunc();

If however, you have created a static method something like:

static $foo; // your top variable set as static

public static function foobarfunc() {
    return self::$foo;
}

then you can use this:

foobar::foobarfunc();

You are calling a non-static method :

public function foobarfunc() {
    return $this->foo();
}

Using a static-call :

foobar::foobarfunc();

When using a static-call, the function will be called (even if not declared as static), but, as there is no instance of an object, there is no $this.

So :

• You should not use static calls for non-static methods
• Your static methods (or statically-called methods) can't use $this, which normally points to the current instance of the class, as there is no class instance when you're using static-calls.

Here, the methods of your class are using the current instance of the class, as they need to access the $foo property of the class.

This means your methods need an instance of the class -- which means they cannot be static.

This means you shouldn't use static calls : you should instanciate the class, and use the object to call the methods, like you did in your last portion of code :

$foobar = new foobar();
$foobar->foobarfunc();

For more informations, don't hesitate to read, in the PHP manual :

• The Classes and Objects section
• And the Static Keyword page.

Also note that you probably don't need this line in your __construct method :

global $foo;

Using the global keyword will make the $foo variable, declared outside of all functions and classes, visibile from inside that method... And you probably don't have such a $foo variable.

To access the $foo class-property, you only need to use $this->foo, like you did.