C# try-catch块内的变量范围

尝试关闭Finally代码块中的文件时出错：

static void Main(string[] args)
{
    try
    {
        StreamReader myReader = new StreamReader("c:\\j\\MyFile1.txt");

        string line = "";

        while (line != null)
        {
            line = myReader.ReadLine();
            Console.WriteLine(line);
        }

        //myReader.Close();
    }
    catch (FileNotFoundException e)
    {
        Console.WriteLine("sorry file not found! {0}", e.Message);
    }
    catch (DirectoryNotFoundException e)
    {
        Console.WriteLine("You have given the wrong path for the file! {0}", e.Message);
    }
    catch (Exception e)
    {
        Console.WriteLine("Sorry you typed in a wrong file name! {0}", e.Message);
    }
    finally
    { 
        myReader.Close();
    }

    Console.ReadLine();
}

您需要在try/catch/finally块之外声明StreamReader实例

---

您需要在try上面声明StreamReader

尽管如此，我还是建议在本例中使用using语句而不是try/finally，因为它是专门为资源清理而设计的

using (StreamReader myReader = new StreamReader("c:\\j\\MyFile1.txt"))
{
    try
    {
        string line = "";

        while (line != null)
        {
            line = myReader.ReadLine();
            Console.WriteLine(line);
        }
    }
    catch (FileNotFoundException e)
    {
        Console.WriteLine("sorry file not found! {0}", e.Message);
    }
    catch (DirectoryNotFoundException e)
    {
        Console.WriteLine("You have given the wrong path for the file! {0}", e.Message);

    }
    catch (Exception e)
    {
        Console.WriteLine("Sorry you typed in a wrong file name! {0}", e.Message);
    }
}

Console.ReadLine();

这将保证StreamReader是关闭的，但要以更为idomatic的方式进行。StreamReader的IDisposable.Dispose实现将关闭流

只需在try块外定义myReader，并在finally块中检查null，然后调用close

StreamReader myReader = null;
try
{
    myReader = new StreamReader("c:\\j\\MyFile1.txt");
    //.....

在最后一个街区

finally
{ 
    // Performs the operations that should be accomplished for eg closing the connections, file, database
    if(myReader != null)
        myReader.Close();
}

---

在尝试之前声明变量：

StreamReader myReader = null;

等等。然后在try块中设置它们。

这样做

StreamReader myReader = null;
try
        {

           myReader  = new StreamReader("c:\\j\\MyFile1.txt");
            string line = "";

            while (line != null)
            {
                line = myReader.ReadLine();
                Console.WriteLine(line);


            }

            //myReader.Close();
        }

        catch (FileNotFoundException e)
        {
            Console.WriteLine("sorry file not found! {0}", e.Message);

        }

        catch (DirectoryNotFoundException e)
        {
            Console.WriteLine("You have given the wrong path for the file! {0}", e.Message);

        }



        catch (Exception e)
        {
            Console.WriteLine("Sorry you typed in a wrong file name! {0}", e.Message);


        }

        finally
        { 
            // Performs the operations that should be accomplished for eg closing the connections, file, database
            if(myReader !=null)
            myReader.Close();

        }



        Console.ReadLine();


    }
}

---

您是要告诉我们错误还是我们猜猜看？错误：名称“myReader”在当前上下文中不存在，因为它的作用域在块中，所以可以保留在try块中。请通过代码示例说明这一点，因为我尝试在try块外声明它，但它不工作。错误：名称“myReader”在当前上下文谢谢大家在那里帮助我！我在你们的帮助下修好了！上帝保佑，谢谢你们每个人帮助我！我在你们的帮助下修好了！上帝保佑！

StreamReader myReader = null;
try
        {

           myReader  = new StreamReader("c:\\j\\MyFile1.txt");
            string line = "";

            while (line != null)
            {
                line = myReader.ReadLine();
                Console.WriteLine(line);


            }

            //myReader.Close();
        }

        catch (FileNotFoundException e)
        {
            Console.WriteLine("sorry file not found! {0}", e.Message);

        }

        catch (DirectoryNotFoundException e)
        {
            Console.WriteLine("You have given the wrong path for the file! {0}", e.Message);

        }



        catch (Exception e)
        {
            Console.WriteLine("Sorry you typed in a wrong file name! {0}", e.Message);


        }

        finally
        { 
            // Performs the operations that should be accomplished for eg closing the connections, file, database
            if(myReader !=null)
            myReader.Close();

        }



        Console.ReadLine();


    }
}