在遍历StreamReader对象列表时返回空引用异常 [英] Null reference exception while iterating over a list of StreamReader objects

问题描述

我正在制作一个简单的程序，在一组文件中搜索一个特定的名称。我有大约23个文件需要通过。为了实现这个功能，我使用了 StreamReader 类，因此编写了更少的代码，我做了一个

 列表与LT; StreamReader的> FileList = new List< StreamReader>（）; 
  

包含StreamReader类型元素的列表，我的计划是迭代列表并打开每个文件： / b>

  foreach（FileList中的StreamReader元素）
（！Element.EndOfStream）
 {
 //在此处处理文件的代码。 
 
 
 
 
 $ b我打开了FileList中的所有流。问题是我得到一个 
 
 
 
 
空引用异常
 
 
 
 $ 
 
 
有人可以告诉我我在这里做了什么错误，为什么我得到这个异常，什么是我可以采取哪些步骤来纠正这个问题？
解决方案
如上所述，使用以下方法： b 
 $ b 
 使用（StreamReader sr = new StreamReader（filename.txt））
 {
 ... 
 } 
  
如果您要将名称存储在列表中，建议您使用字典： 
 
 
 字典< string，string> Files = new Dictionary< string，string>（）; 
 
使用（StreamReader sr = new StreamReader（filename.txt））
 {
 string total =; 
字符串行; （（line = sr.ReadLine（））！= null）
（
 total + = line; 
} 
 Files.Add（filename.txt，line）; 
 
 $ / code> 
访问它们：
 
 
  Console.WriteLine（Filename.txt has：+ Files [filename.txt]）; 
  
或者如果您想获取StreamReader它自己不是文件文本，您可以使用：
 字典< string，StreamReader> Files = new Dictionary< string，StreamReader>（）; 
 
使用（StreamReader sr = new StreamReader（filename.txt））
 {
 Files.Add（filename.txt，sr）; 
} 
  
 
I am making a simple Program which searches for a particular Name in a set of files.I have around 23 files to go through. To achieve this I am using  StreamReader class, therefore, to write less of code, I have made a 
List<StreamReader> FileList = new List<StreamReader>();
list containing elements of type StreamReader and my plan is to iterate over the list and open each file:
foreach(StreamReader Element in FileList)
{
    while (!Element.EndOfStream)
    {
        // Code to process the file here.
    }
}
I have opened all of the streams in the FileList.The problem is that I am getting a 

  
Null Reference Exception 
at the condition in the while loop.


Can anybody tell me what mistake I am doing here and why I am getting  this exception and what are the steps I can take to correct this problem?
解决方案
As peoples described on above, Use the following way:
using (StreamReader sr = new StreamReader("filename.txt"))
{
    ...
}
If you're trying to store files with their names on a list, I suggest you to use a dictionary:
Dictionary<string, string> Files = new Dictionary<string, string>();

using (StreamReader sr = new StreamReader("filename.txt"))
{
   string total = "";
   string line;
   while ((line = sr.ReadLine()) != null)
   {
      total += line;
   }
   Files.Add("filename.txt", line);
}
To access them:
Console.WriteLine("Filename.txt has: " + Files["filename.txt"]);
Or If you want to get the StreamReader It self not the file text, You can use:
Dictionary<string, StreamReader> Files = new Dictionary<string, StreamReader>();

using (StreamReader sr = new StreamReader("filename.txt"))
{
    Files.Add("filename.txt", sr);
}


                        
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