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捕获C#2.0中作为类型参数给出的异常类型

exception generics .net c#

2

jyoungdev Thilo · 技术社区 · 16 年前

    /// <summary>
    /// asserts that running the command given throws an exception.
    /// </summary>
    public static void Throws<ExceptionType>(ICommand cmd)
        where ExceptionType : Exception
    {
        // Strangely, using 2 catch blocks on the code below makes the first catch block do nothing.
        try
        {
            try
            {
                cmd.Execute();
            }
            catch (ExceptionType)
            {
                return;
            }
        }
        catch (Exception f)
        {
            throw new AssertionException(cmd.ToString() + " threw an exception of type " + f.GetType() + ".  Expected type was " + typeof(ExceptionType).Name + ".");
        }

        throw new AssertionException(cmd.ToString() + " failed to throw a " + typeof(ExceptionType).Name + ".");
    }

    [Test]
    public void Test_Throws_CatchesSpecifiedException()
    {
        AssertThat.Throws<AssertionException>(
            new FailureCommand()
        );
    }

class FailureCommand : ICommand
{
    public object Execute()
    {
        Assert.Fail();
        return null;    // never reached.
    }

    public override string ToString()
    {
        return "FailureCommand";
    }
}

在NUnit中提供以下输出:

TestUtil.Tests.AssertThatTests.Test_抛出捕获指定异常: FailureCommand引发了NUnit.Framework.AssertionException类型的异常。预期类型为AssertionException。

我还尝试使用2个catch块来创建1个try块(而不是在外部try中嵌套try/catch),但得到了相同的结果。

3 回复 | 直到 16 年前

1

3

Jon Skeet 16 年前

在这项测试中,我感觉很好:

using System;
using System.IO;

class Test
{
    static void Main()
    {
        Throws<ArgumentNullException>(() => File.OpenText(null));
    }

    public static void Throws<ExceptionType>(Action cmd)
        where ExceptionType : Exception
    {
        try
        {
            try
            {
                cmd();
            }
            catch (ExceptionType)
            {
                Console.WriteLine("Caught!");
                return;
            }
        }
        catch (Exception f)
        {
            Console.WriteLine("Threw an exception of type " + f.GetType() 
                + ".  Expected type was " + typeof(ExceptionType) + ".");
        }

        Console.WriteLine("No exception thrown");
    }
}

你有多确定这两个 AssertionException 例外情况相同吗?它们是否确实在同一名称空间中(打印) typeof(ExceptionType)

请尝试一个例外,而不是让生活更简单。

2

1

Community Mohan Dere 9 年前

有关详细信息,请参阅此线程: Why can't I catch a generic exception in C#?

https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=362422&wa=wsignin1.0

3

0

sidney.andrews 16 年前

我没有调试这段代码,也没有看太久,但可能是您的第一个“return”语句导致代码停止并离开该方法。因此,异常被“捕获”或“处理”(不管您怎么看),外部try/catch块永远不会执行。

你想这么做吗?

try        
{            
    try            
    {                
        cmd.Execute();            
    }            
    catch (ExceptionType)            
    {                
        throw;
    }        
}        
catch (Exception f)        
{            
    throw new AssertionException(cmd.ToString() + " threw an exception of type " + f.GetType() + ".  Expected type was "  + typeof(ExceptionType).Name + ".");        
}