Reflection.Assembly.CreateInstance(字符串)

发布于 2024-12-13 04:30:10 字数 445 浏览 1 评论 0原文

在.NET 4.0中，如果我有以下代码：

....
T instantiatedClass;
try
{
    instantiatedClass = (T)assembly.CreateInstance(classFullName);
}
catch (Exception ex)
{
    errMsg = string.Format("Error creating an instance of type \"{0}\".", classes.First().FullName);
    throw new ApplicationException(errMsg, ex);
}

假设classFullName是程序集中的正确类型，并且类型“T”实现公共接口，是否存在以下情况：1）不会抛出异常，并且2 ) instantiatedClass 将为 null？

感谢您的任何帮助。

原文

In .NET 4.0, if I have the following code:

....
T instantiatedClass;
try
{
    instantiatedClass = (T)assembly.CreateInstance(classFullName);
}
catch (Exception ex)
{
    errMsg = string.Format("Error creating an instance of type \"{0}\".", classes.First().FullName);
    throw new ApplicationException(errMsg, ex);
}

Assuming that classFullName is a correct type in the assembly, and that the type "T" implements a public interface, is there any circumstance where 1) No exception would be thrown, and 2) instantiatedClass would be null?

Thanks for any help.

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泪冰清 2024-12-20 04:30:10

根据您的假设，如果您的类型 T 始终是一个接口，那么如果所创建的实例未实现相关接口，或者该类型没有可以调用的默认构造函数，则直接转换为 T 将引发异常。

避免引发异常的更好方法是...

T interfaceVar = assembly.CreateInstance(classFullName) as T;
if (interfaceVar == null)
{
    // oops, does not implement interface T
}
else
{
    // yippee, it does implement interface T
}

您可以在目标程序集上使用反射来检查所需的类型是否存在，它是否具有默认构造函数以及它是否实现您感兴趣的接口。在这种情况下，您如果您只想知道它是否具有指定的接口，那么将根本避免创建实例。

Based on your assumptions and if your type T is always an interface then a direct cast to T will throw an exception if the interface in question is not implemented by the created instance or if the type does not have a default constructor that can be called.

A better approach that avoids throwing an exception would be...

T interfaceVar = assembly.CreateInstance(classFullName) as T;
if (interfaceVar == null)
{
    // oops, does not implement interface T
}
else
{
    // yippee, it does implement interface T
}

You could use reflection on the target assembly to check if the required type exists, if it has a default constructor and if it implements the interface you are interested in. In that case you would avoid creating an instance at all, if all you want to know is if it has the specified interface.

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