这是什么作用？？这里的符号意思是

发布于 2024-09-26 06:44:35 字数 852 浏览 1 评论 0原文

可能的重复：
什么是“??”运算符？

这里的 ?? 符号是什么意思？

我说得对吗：使用id，但如果id为空，则使用字符串“ALFKI”？

public ActionResult SelectionClientSide(string id)
        {
            ViewData["Customers"] = GetCustomers();
            ViewData["Orders"] = GetOrdersForCustomer(id ?? "ALFKI");
            ViewData["id"] = "ALFKI";
            return View();
        }
        [GridAction]
        public ActionResult _SelectionClientSide_Orders(string customerID)
        {
            customerID = customerID ?? "ALFKI";
            return View(new GridModel<Order>
            {
                Data = GetOrdersForCustomer(customerID)
            });
        }

原文

Possible Duplicate:
What is the “??” operator for?

What does the ?? notation mean here?

Am I right in saying: Use id, but if id is null use string "ALFKI" ?

public ActionResult SelectionClientSide(string id)
        {
            ViewData["Customers"] = GetCustomers();
            ViewData["Orders"] = GetOrdersForCustomer(id ?? "ALFKI");
            ViewData["id"] = "ALFKI";
            return View();
        }
        [GridAction]
        public ActionResult _SelectionClientSide_Orders(string customerID)
        {
            customerID = customerID ?? "ALFKI";
            return View(new GridModel<Order>
            {
                Data = GetOrdersForCustomer(customerID)
            });
        }

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遇到 2024-10-03 06:44:35

这是空合并运算符。

var x = y ?? z;

// is equivalent to:
var x = (y == null) ? z : y;

// also equivalent to:
if (y == null) 
{
    x = z;
}
else
{
    x = y;
}

即：xy为null，code>将被分配z，否则将被分配y。
因此，在您的示例中，如果 customerID 最初为 null，则它将设置为 "ALFKI"。

That's the null-coalescing operator.

var x = y ?? z;

// is equivalent to:
var x = (y == null) ? z : y;

// also equivalent to:
if (y == null) 
{
    x = z;
}
else
{
    x = y;
}

ie: x will be assigned z if y is null, otherwise it will be assigned y.
So in your example, customerID will be set to "ALFKI" if it was originally null.