codeigniter自定义库未定义属性错误

我为我的支付网关创建了一个代码点火器自定义库（My_payment_gate_way_init）。。但是当我使用我的自定义库函数时，控制器（计费）没有将参数传递到库中，它显示

A PHP Error was encountered
Severity: Notice
Message: Undefined property: Billing::$My_payment_gate_way_init
Filename: controllers/Billing.php
Line Number: 576

当我使用时会出现错误

控制器

    public function __construct()
        {
            parent::__construct();
            $this->load->library('My_payment_gate_way_init');
    }
function saveord(){
$ammount = $this->totlCost * 100;
$this->My_payment_gate_way_init->setTransactionAmountforPay($ammount);
}

库

class My_payment_gate_way_init
{
    private $clientConfig;
    private $initRequest;
    private $transactionAmount;
    private $redirect;
    private $initResponse;
    private $client;
    private $CI;
    function __construct()
    {
 $this->setTransactionAmountforPay();
}
  function setTransactionAmountforPay($ammount=200){
        // sets transaction-amounts details (all amounts are in cents)
        $this->transactionAmount = new TransactionAmount();
        $this->transactionAmount->setTotalAmount(0);
        $this->transactionAmount->setServiceFeeAmount(0);
        $this->transactionAmount->setPaymentAmount($ammount);
        $this->transactionAmount->setCurrency("LKR");
        $this->initRequest->setTransactionAmount($this->transactionAmount);
    }

它还在底部显示了这个错误

致命错误：调用上的成员函数setTransactionAmountforPay（）中为nullC： 上的''axamp''htdocs''debug_online''application''controllers''Billing.php576线