get order id in Observer on sales_order_invoice_save_after

Question

I want order id in observe function but I am getting null I am using this code Observe.php

public function invoiceexport(Varien_Event_Observer $event=null){
    $_helper = Mage::helper('Nino_invoiceexport');
    $importStartDateTime = date('Y-m-d H:i:s');
    $orders = $event->getOrder();
    print_r($orders);
    die;
}

My config.xml is as :

<events>
    <sales_order_invoice_save_after>
         <observers>
             <Nino_invoiceexport_order_invoice_save_after>
                  <type>singleton</type>
                  <class>Nino_InvoiceExport_Model_Observer</class>
                  <method>invoiceexport</method>
              </Nino_invoiceexport_order_invoice_save_after>
          </observers>
     </sales_order_invoice_save_after>
</events>

Answer 1

You can get orderId by using this way,

    $invoice = $observer->getEvent()->getInvoice();
    $order = $invoice->getOrder();
    $orderId=$order->getId();