How can I get $id variable in widget's form function?

Question

How can I get $id variable in widget's form function? According to widget's structure I see that widget function have $args as a parameter, which will be extracted in function's body. In my case i want to use $id variable (from extracted $args) which contains current sidebar's id. How can I make 'visible' $id variable in form function? Any ideas?

class Ex_Widget_Example extends WP_Widget {
    //constructor goes here
    function widget($args, $instance) {extract($args);}
    function update($new_instance, $old_instance ) { }
    function form( $instance ) {}
}

For example we have sidebar with id 'my_sidebar'. I put this widget in it. For example my widget function, which we use to output something on page, looks like this:

function widget($args, $instance) {
         extract($args);
         echo $id; //or just echo $args['id'];
}

So on my page, in my 'my_sidebar' sidebar I will see a text 'my_sidebar'. That's great. But how can I get this $id or $args['id'] in widget's form function. In class example I see, that only widget function takes $args as argument. I'm not an expert in OOP pragramming, I tried to create a static variable (unsuccessfully), which would keep id value:

class Ex_Widget_Example extends WP_Widget {
    public static $widget_id;
    //constructor goes here
    function widget($args, $instance) {
             extract($args);
             self::$widget_id = $id;
             echo self::$widget_id //here outputs sidebar's id perfectly on my page
    }
    function update($new_instance, $old_instance ) { }
    function form( $instance ) {
             echo self::$widget_id //here outputs nothing on my widget's form
    }
}

Maybe wordpress call form function first, before widget function, that's why I can't see anything on my form ....anyway, any ideas how to solve this problem?

Answer 1

Do you search for $args['widget_id']? Just save it in a variable you can access in form() later.

Look at wp-includes/default-widgets.php to see how widgets work. Not the best code, but it should give you some hints.

Answer 2

As a follow up on @toscho answer, you maybe could get the current sidebar (that holds the widget) via the DB options table:

$current_sidebar = array_search( 
    "{$this->id_base}-{$this->number}", 
    get_option( 'sidebars_widgets' ), 
    true 
);

Not tested

Answer 3

The following worked for me inside the function for the form

public function form( $instance ) {
    $my_widget = $this;
    $widget_identifier = "{$this->id_base}-{$this->number}";
}

Edit: the following also works

public function form( $instance ) {
    $widget_identifier = $this->id;
}