空检查后的NullReferenceException抛出？ [英] NullReferenceException thrown after null check?

问题描述

所以，我跟踪不同用户通过GUID访问。它曾大到现在为止，我不明白为什么它的失败。

我赋予该变量，然后我检查空，然后运行code，然后把它抛出NullReferenceException异常错误。这里是code：

 如果（String.IsNullOrEmpty（会话[GUID]作为字符串））
    {
        Server.Transfer的（〜/的Index.aspx，真正的）;
    }
    其他
    {
        GUID =会话[GUID]的ToString（）。
        如果（！String.IsNullOrEmpty（GUID））
        {
            ITEMID =（INT）aooDB_Items.SelectItemID（GUID）;
        }
    }
 

该NullReferenceException异常被抛出在aooDB_Items.SElectItemID（GUID）行

更新：我也尝试设置GUID =无，然后检查，以确保它不是无的办code之前。在code运行在每个时间，如果我把一个断点在任何地方我可以看到GUID都有一个GUID为一个值，这使得这更混乱。

错误：

 键入System.NullReferenceException的异常App_Web_3hq5xlxh.dll发生，但在用户code没有处理

    其他信息：未将对象引用设置到对象的实例。
 

解决方案

插图中和罗比Cornelissen帮我解决这个问题。问题是，SelectItemID被发回什么。

So I track different users access through GUID. It has worked great up until now and I dont understand why its failing.

I am assigning the variable, then I check for null, then run the code, and then it throws the nullreferenceexception error. Here is the code:

    if (String.IsNullOrEmpty(Session["GUID"] as string))
    {
        Server.Transfer("~/index.aspx", true);
    }
    else
    {
        GUID = Session["GUID"].ToString();
        if (!String.IsNullOrEmpty(GUID))
        {
            itemID = (int)aooDB_Items.SelectItemID(GUID);
        }
    }

The NullReferenceException is being thrown in the aooDB_Items.SElectItemID(GUID) line

Update: I also tried setting GUID = "none" and then checking to make sure its not "none" before running the code. The code runs each time and if I put a breakpoint in anywhere I can see that GUID has a GUID as a value which makes this more confusing.

Error:

    An exception of type 'System.NullReferenceException' occurred in App_Web_3hq5xlxh.dll but was not handled in user code

    Additional information: Object reference not set to an instance of an object.

解决方案

InBetween and Robby Cornelissen helped me solve this problem. The issue was that SelectItemID was sending back nothing.

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