managementObject和不同的null警告

Question

我在.net 6和VS 2022中有以下代码。为了保持轻松，我评论了这条线后面的警告。我不知道怎么解决这个问题。希望有人能帮我。

try
{
var searcher = new ManagementObjectSearcher("SELECT * FROM Win32_ComputerSystem");
using (ManagementObjectCollection managementObjectCollection = searcher.Get())
{
ManagementObject? managementObject = managementObjectCollection.OfType<ManagementObject>().FirstOrDefault();
hardwareComputerName = managementObject["name"].ToString().ToLower(); // 'managementObject' may be null here. CS8602 Dereference of a possibly null reference. (2x)
hardwareComputerManufacturer = managementObject["Manufacturer"].ToString(); // 'managementObject' is not null here. CS8601 Possible null reference assignment.
hardwareComputerModel = managementObject["model"].ToString(); // 'managementObject' is not null here. CS8601 Possible null reference assignment.
}
}
catch (Exception)
{
MessageBox.Show("Problem im Abschnitt Name, Hersteller und Modell.");
}

Answer 1

managementObject可能是null(它可以为null，FirstOrDefault可能返回null(，并且在其声明后的行上，您访问managementObject的一个成员而不首先验证它是否为null，这可能会导致null引用异常，因此会发出警告。

你有几个选择，其中两个是

1. 用First替换FirstOrDefault；如果找不到元素，但结果从不为null，则将抛出

2. 测试null，如果不是null，则仅执行成员访问语句

   管理对象？managementObject=。。。FirstOrDefault((；

   if(null！=managementObject({。。。}

Answer 2

这是没有给出警告的代码。感谢Moho的帮助。

try
{
var searcher = new ManagementObjectSearcher("SELECT * FROM Win32_ComputerSystem");
using (ManagementObjectCollection managementObjectCollection = searcher.Get())
{
ManagementObject? managementObject = managementObjectCollection.OfType<ManagementObject>().First();
hardwareComputerName = managementObject["name"].ToString()?.ToLower() ?? "Default";
hardwareComputerManufacturer = managementObject["Manufacturer"].ToString() ?? "Default";
hardwareComputerModel = managementObject["model"].ToString() ?? "Default";
}
}
catch (Exception)
{
MessageBox.Show("Problem im Abschnitt Name, Hersteller und Modell.");
}