[英]Reading from file and writing to a temporary .txt file in C#?
我知道这个网站上有很多类似的主题,但我认为我经历了大部分,仍然无法调试这段代码。 我真的需要让这个工作。 我是 C# 和编程的新手。 Tho,我在 Java 中做了同样的任务,但由于某种原因,我不能让它在这里工作。 如果有人可以请投...
所以我有一些对象,我保存在.txt
文件中,一行 = 一个 object 的数据。 该行的第一个数据是 object 的Id
,基本上是主键。 现在我正在实现CRUD
操作,即更新。 此编辑 function 应该有助于该功能。
如果用户编辑某些选定的 object 属性,则该更改需要反映在.txt
文件中。 So, I will go through every object/line in the file, write them to some temp.txt
file, once I hit object which has same Id
as the passed object o
, that means I need to write that edited object
to temp.txt
. 之后,我需要将temp.txt
重命名为原始文件并删除temp.txt
。
我尝试了一堆选项和组合,但没有一个奏效。
我确实确保GetTxtPath
从我的项目中返回正确的绝对路径。
版本 1:
public static void edit(Transformable o, string fileName)
{
try
{
if (!File.Exists(FileUtils.GetTxtPath("temp.txt")))
{
File.Create(FileUtils.GetTxtPath("temp.txt"));
}
using (FileStream stream = File.OpenRead(FileUtils.GetTxtPath(fileName)))
using (FileStream writeStream = File.OpenWrite(FileUtils.GetTxtPath("temp.txt")))
{
StreamReader reader = new StreamReader(stream);
StreamWriter writer = new StreamWriter(writeStream);
String line;
while ((line = reader.ReadLine()) != null)
{
if (!line.Equals(""))
{
if (o.GetId() == getIdFromString(line))
{
writer.Write(o.WriteToFile());
}
else
{
writer.Write(line + "\n");
}
}
else
{
continue;
}
}
}
}
catch (FileNotFoundException e)
{
Console.WriteLine($"The file was not found: '{e}'");
}
catch (DirectoryNotFoundException e)
{
Console.WriteLine($"The directory was not found: '{e}'");
}
catch (IOException e)
{
Console.WriteLine($"The file could not be opened: '{e}'");
}
}
public static string GetTxtPath(string fileName)
{
var startDirectory =
Directory.GetParent(Directory.GetCurrentDirectory()).Parent.Parent.FullName;
var absPath = startDirectory + @"\data\" + fileName;
return absPath;
}
private static int getIdFromString(string line)
{
return Int32.Parse(line.Split('|')[0]);
}
版本 2:
public static void Edit(Transformable o, string fileName)
{
try
{
if (!File.Exists(FileUtils.GetTxtPath("temp.txt")))
{
File.Create(FileUtils.GetTxtPath("temp.txt"));
}
using (StreamReader reader = FileUtils.GetTxtReader(fileName))
using (StreamWriter writer = FileUtils.GetTxtWriter("temp.txt"))
{
String line;
while ((line = reader.ReadLine()) != null)
{
if (!line.Equals(""))
{
if (o.GetId() == getIdFromString(line))
{
writer.Write(o.WriteToFile());
}
else
{
writer.Write(line + "\n");
}
}
else
{
continue;
}
}
}
File.Move(FileUtils.GetTxtPath("temp.txt"), FileUtils.GetTxtPath(fileName));
File.Delete(FileUtils.GetTxtPath("temp.txt"));
//Here I tied many differenet options but nonthing worked
//Here is Java code which did the job of renaming and deleting
//------------------------------------------------------------
// File original = FileUtils.getFileForName(fileName);
// File backUpFile = new File("backUp");
// Files.move(original.toPath(), backUpFile.toPath(),
// StandardCopyOption.REPLACE_EXISTING);
// File temporary = FileUtils.getFileForName(temporaryFilePath);
// temporary.renameTo(original);
// backUpFile.delete();
// File original = FileUtils.getFileForName(path);
//--------------------------------------------------------
//public static File getFileForName(String name)
//{
// String dir = System.getProperty("user.dir");
// String sP = System.getProperty("file.separator");
// File dirData = new File(dir + sP + "src" + sP + "data");
// File file = new File(dirData.getAbsolutePath() + sP + name);
// return file;
//}
//---------------------------------------------------------------------
}
catch (FileNotFoundException e)
{
Console.WriteLine($"The file was not found: '{e}'");
}
catch (DirectoryNotFoundException e)
{
Console.WriteLine($"The directory was not found: '{e}'");
}
catch (IOException e)
{
Console.WriteLine($"The file could not be opened: '{e}'");
}
public static StreamReader GetTxtReader(string fileName)
{
var fileStream = new FileStream(GetTxtPath(fileName), FileMode.Open, FileAccess.Read);
return new StreamReader(fileStream, Encoding.UTF8);
}
public static StreamWriter GetTxtWriter(string fileName)
{
FileStream fileStream = new FileStream(GetTxtPath(fileName), FileMode.Append);
return new StreamWriter(fileStream, Encoding.UTF8);
}
public static void Edit(Transformable o, string fileName)
{
try
{
string tempName = "temp.txt"; // create here correct path
using (var readStream = File.OpenRead(fileName))
using (var writeStream = File.OpenWrite(tempName))
using (var reader = new StreamReader(readStream))
using (var writer = new StreamWriter(writeStream))
{
string line;
while ((line = reader.ReadLine()) != null)
{
if (!line.Equals(""))
{
if (o.GetId() == GetId(line))
{
writer.WriteLine(o.ToWriteableString());
}
else
{
writer.WriteLine(line);
}
}
}
}
File.Delete(fileName);
File.Move(tempName, fileName);
}
catch ...
}
File.OpenWrite
方法打开现有文件或创建新文件以进行写入。 因此无需手动检查和创建文件。
您已经非常正确地将FileStreams
包装在 using 语句中。 但是, StreamReader
和StreamWriter
也必须在使用后释放。
我重命名了一些方法,赋予它们符合 C# 中命名规则的名称: Edit
、 GetId
、 ToWriteableString
。
不需要带有continue
语句的else
分支。
最后,只需使用File.Delete
和File.Move
方法。
注意: int.Parse
方法可以抛出同样需要处理的异常。
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