如何知道内置异常或用户定义的异常

您应该定义一个自定义异常类,并使用专用的catch块检查该类。

通过从 Exception 类别:

public class MyException : Exception
{
    public MyException() { }

    public MyException(string message)
        : base(message)
    { }
}

然后在代码中抛出该异常类型:

void MyMethod()
{
    int a;
    try
    {
        Console.Write("Input = ");
        a = Convert.ToInt32(Console.ReadLine());
        if (a < 0)
        {
            throw new MyException("Input Can't < 0");
        }
    }
    catch (MyException myEx)
    {
        Console.WriteLine("MyException was thrown");
    }
    catch (Exception ex)
    {
        Console.WriteLine("Some other exception was thrown");
    }
    Console.ReadKey();
}