C# 检查对象是否为空 [英] C# Checking if Object is Null

问题描述

我在使用 if 语句检查对象是否为空时遇到问题.

I am having trouble with an if statement for checking if an object is null.

我有一个 webClient 去尝试从网站中提取一个 JSON 字符串.如果出错，那是因为 API 中不存在 3 位国家，我只想跳过它.

I have a webClient go and pull a JSON string from a website in a try/catch. If it errors, it is because the 3 digit country does not exist in the API and I just want to skip it.

这是我的代码:

    System.Net.WebClient wc = new System.Net.WebClient();

    RootObject ro;
    try
    {
        string resp = wc.DownloadString("https://restcountries.eu/rest/v2/alpha/" + Row.Code.ToString());

        JavaScriptSerializer js = new JavaScriptSerializer();

        ro = js.Deserialize<RootObject>(resp);
    }
    catch (Exception e)
    { }

    if (ro.Region != null)
    {
        Row.Region = ro.Region;
        Row.SubRegion = ro.Subregion;
    }

RootObject 是一个要反序列化的类.这工作正常.

RootObject is a class to deserialize to. This works fine.

但是，我在 if 语句中收到一个错误，即使用未分配的类 'ro'.

However, I am getting an error in the if statement that "use of unassigned class 'ro'.

有人可以帮我解决这个问题吗?ro 在 if 内按预期工作?

Can someone help me fix this? ro works as expected inside the if?

我也试过检查一个特定的节点，但它仍然挂在ro"部分.

I have also tried checking a specific node and it is still getting hung up on the 'ro' part.

此外，这是 SSIS 中的脚本组件.

Also, this is a script component in SSIS.

谢谢

推荐答案

1. try 块可能永远不会为 ro 赋值，因此它会在 try 块之外未分配.要解决这个问题，请分配一个值:

1. It is possible that the try block will never assign a value to ro and thus it will be unassigned outside of try block. To fix that, assign a value:

RootObject ro = null;

由于 ro 可能是 null，您需要在尝试访问成员之前在 if 语句中检查它:

Since ro could be null, you need to check for that in your if statement before you try to access a member:

if (ro != null && ro.Region != null)
{
    Row.Region = ro.Region;
    Row.SubRegion = ro.Subregion;
}

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