读取空文本文件问题 [英] Reading an empty text file problem

问题描述

朋友们，
作为我正在开发的软件的一部分，通过安装安装将一个空的文本文件("filex.txt")放入与可执行文件相同的文件夹中.在软件注册时，我将激活状态(只是一个字符串)写入此文件，并且在每次启动时，我都会读取此文件的内容以验证注册.问题是，当我运行该软件时出现错误，因此我将该位隔离到测试项目中，但仍然出现错误.我捕获到的异常消息说:对象引用未设置为对象的实例".我在测试项目中尝试过的一些代码如下所示:

Hi friends,
As part of a software I am working on, an empty text file("filex.txt") is put into the same folder as the executable by setup installation. I write the activation status(which is just a string) to this file on registration of the software and at every start-up, I read the content of this file to verify registration. The problem is that I get an error when I run that bit of the software so I isolated that bit into a test project and still get an error. The Exception message that I caught says: "Object Reference not set to an instance of an object". The bit of code I tried in the test project is shown below:

//create a streamreader for the filex.txt file
                StreamReader reader = new StreamReader(pathfu);
                try
                {
                    string rline = reader.ReadLine();
                    
                    MessageBox.Show(rline.Trim());
                    MessageBox.Show("This was successful, Thank you");
                }
                catch (Exception ex)
                {
                    MessageBox.Show("The error is: " + ex.Message);
                }
                finally
                {
                    reader.Close();
                }

推荐答案

尝试一下:

Try this:

if (reader != null)
{
    string rline = reader.ReadLine();
    if (!string.IsNullOrEmpty(rline))
    {
        MessageBox.....
    }
}

尝试:

string rline = reader.ReadLine();
if (rline != null)
   {
   MessageBox.Show(rline.Trim());
   MessageBox.Show("This was successful, Thank you");
   }

如果您查看 StreamReader.ReadLine [

If you look at StreamReader.ReadLine[^] it returns null if the end of the file is encountered.

ReadLine()方法的工作方式类似于也等于0和ReadBuffer()方法0 ，然后是ReadLine() 方法return null.
结果，您正在null 到rline.

因此很明显，我们无法从空对象调用方法(在本例中为Trim().

这可能会有所帮助，

ReadLine() method of StreamReader class works like, if the charLen and charPos (private members of the StreamReader class) is equal to 0 and ReadBuffer() method 0 as well, then ReadLine() method return null.
As a result You are getting null to rline.

So it is clear that we cannt call a method( in this case Trim() ) from a null object.

It might be helpful,

class Program
    {

        static void Main(string[] args)
        {
            ReadFromFile("C:\\Temp\\Test2.txt");
        }

        public static void ReadFromFile(string fileToRead)
        {
            if (File.Exists(fileToRead))
            {
                using (StreamReader reader = new StreamReader(fileToRead))
                {
                    string lineOfData = default(string);
                    if ((lineOfData = reader.ReadLine()) != null)
                    {
                        var rr = lineOfData.Trim();
                    }
                }
            }
        }
    }

:)

:)

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