try/catch 不适用于 using 语句

Question

try
    {
        using (response = (HttpWebResponse)request.GetResponse())
            // Exception is not caught by outer try!
    }
    catch (Exception ex)
    {
        // Log
    }

编辑：

// Code for binding IP address:
ServicePoint servicePoint = ServicePointManager.FindServicePoint(uri);
servicePoint.BindIPEndPointDelegate = new BindIPEndPoint(Bind);
//
private IPEndPoint Bind(ServicePoint servicePoint, IPEndPoint remoteEndPoint, int retryCount)
    {
        IPAddress address;

        if (retryCount < 3)
            address = IPAddress.Parse("IPAddressHere");
        else
            {
                address = IPAddress.Any;
                throw new Exception("IP is not available,"); // This exception is not caught
            }

        return new IPEndPoint(address, 0);
    }

Answer 1

我可以想象，如果您在 using 块中创建一个单独的线程，就会发生这种情况。如果那里抛出异常，一定要在那里处理它。否则，这种情况下的外部 catch 块将无法处理它。

class TestClass : IDisposable
{
    public void GetTest()
    {
        throw new Exception("Something bad happened"); // handle this
    }

    public void Dispose()
    {
    }
}

class Program
{
    static void Main(string[] args)
    {
        try
        {
            using (TestClass t = new TestClass())
            {
                Thread ts = new Thread(new ThreadStart(t.GetTest));
                ts.Start();
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("Error: " + ex.Message);
        }
    }
}

Answer 2

使用后还有更多代码吗？ using 需要一条语句或在 using 语句之后有一个块 { }。在下面的示例中，using 语句内的任何异常都将被 try..catch 块捕获。

try
{
    using (response = (HttpWebResponse)request.GetResponse())
    {
        ....
    }
}
catch (Exception ex)
{
}

Answer 3

这很好用。您将看到 Console.WriteLine() 打印出一个异常

class Program
{
    static void Main(string[] args)
    {
        Foo foo = new Foo();

        try
        {
            using (Bar bar = foo.CreateBar())
            {

            }
        }
        catch(Exception exception)
        {
            Console.WriteLine(exception.Message);
        }
    }
}

public class Foo
{
    public Bar CreateBar()
    {
        throw new ApplicationException("Something went wrong.");
    }
}

public class Bar : IDisposable
{
    public void Dispose()
    {
    }
}

，如果您的意思是在 using 内部抛出异常，那么这可以很好地工作。这还将生成一个控制台语句：

class Program
{
    static void Main(string[] args)
    {
        Foo foo = new Foo();

        try
        {
            using (Bar bar = foo.CreateBar())
            {
                throw new ApplicationException("Something wrong inside the using.");
            }
        }
        catch(Exception exception)
        {
            Console.WriteLine(exception.Message);
        }
    }
}

public class Foo
{
    public Bar CreateBar()
    {
        return new Bar();
        // throw new ApplicationException("Something went wrong.");
    }
}

public class Bar : IDisposable
{
    public void Dispose()
    {
    }
}

Answer 4

using 关键字与 try-catch-finally 相同，http://msdn。 microsoft.com/en-us/library/yh598w02.aspx。基本上，您在 try-catch 中嵌套了一个 try-catch-finally ，这就是您可能如此困惑的原因。

你可以这样做...

class Program
{
    static void Main(string[] args)
    {
        HttpWebResponse response = new HttpWebResponse();
        try
        {
            response.GetResponse();
        }
        catch (Exception ex)
        {
            //do something with the exception
        }
        finally
        {
            response.Dispose();
        }
    }
}