如何在使用FileStream和StreamWriter时删除文件中最旧的行

Question

根据 Prakash 在这里的回答，我想我会尝试这样的事情来删除文件中最古老的行，然后再添加新行：

private ExceptionLoggingService()
{
    _fileStream = File.OpenWrite(GetExecutionFolder() + "\Application.log");
    _streamWriter = new StreamWriter(_fileStream);
}
public void WriteLog(string message)
{
    const int MAX_LINES_DESIRED = 1000;
    StringBuilder formattedMessage = new StringBuilder();
    formattedMessage.AppendLine("Date: " + DateTime.Now.ToString());
    formattedMessage.AppendLine("Message: " + message);
    // First, remove the earliest lines from the file if it's grown too much
    List<string> logList = File.ReadAllLines(_fileStream).ToList();
    while (logList.Count > MAX_LINES_DESIRED)
    {
        logList.RemoveAt(0);
    }
    File.WriteAllLines(_fileStream, logList.ToArray());
    _streamWriter.WriteLine(formattedMessage.ToString());
    _streamWriter.Flush();
}

。但是在我的.NET（Compact Framework，VS 2008中的Windows CE C#项目）中，ReadAllLines（）和WriteAllLines（）都不可用。

ReadAllLines/WriteAllLines挑战完成同样事情的方式是什么？

更新

这无疑是笨拙的，但似乎它应该有效，我将对其进行测试。我将"缩短日志文件"代码从 WriteLog（） 方法移动到构造函数：

private ExceptionLoggingService()
{
    const int MAX_LINES_DESIRED = 1000;
    string uriPath = GetExecutionFolder() + "\Application.log";
    string localPath = new Uri(uriPath).LocalPath;
    if (!File.Exists(localPath))
    {
        File.Create(localPath);
    }
    _fileStream = File.OpenWrite(localPath);
    // First, remove the earliest lines from the file if it's grown too much
    StreamReader reader = new StreamReader(_fileStream);
    List<String> logList = new List<String>();
    while (!reader.EndOfStream)
    {
        logList.Add(reader.ReadLine());
    }
    while (logList.Count > MAX_LINES_DESIRED)
    {
        logList.RemoveAt(0);
    }
    if (logList.Count > MAX_LINES_DESIRED)
    {
        _fileStream.Close();
        File.Delete(GetExecutionFolder() + "\Application.log");
        File.Create(GetExecutionFolder() + "\Application.log");
        _fileStream = File.OpenWrite(GetExecutionFolder() + "\Application.log");
    }
    _streamWriter = new StreamWriter(_fileStream);
    foreach (String s in logList)
    {
        _streamWriter.WriteLine(s);
        _streamWriter.Flush();
    }
}
public void WriteLog(string message)
{
    StringBuilder formattedMessage = new StringBuilder();
    formattedMessage.AppendLine("Date: " + DateTime.Now.ToString());
    formattedMessage.AppendLine("Message: " + message);
    _streamWriter.WriteLine(formattedMessage.ToString());
    _streamWriter.Flush();
}

Answer 1

ReadAllLines和WriteAllLines只是对你隐藏了一个循环。只需做：

StreamReader reader = new StreamReader(_fileStream);
List<String> logList = new List<String>();
while (!reader.EndOfStream)
   logList.Add(reader.ReadLine());

请注意，这与 File.ReadAllLines 的实现几乎相同（来自 MSDN 参考源）

       String line;
        List<String> lines = new List<String>();
        using (StreamReader sr = new StreamReader(path, encoding))
            while ((line = sr.ReadLine()) != null)
                lines.Add(line);
        return lines.ToArray();

WriteAllLines是模拟的：

StreamWriter writer = new StreamWriter(path, false); //Don't append!
foreach (String line in logList)
{
   writer.WriteLine(line);
}

Answer 2

我会为此编写简单的扩展方法，这些方法可以懒惰地完成工作，而无需将整个文件加载到内存中。

用法是这样的：

outfile.MyWriteLines(infile.MyReadLines().Skip(1));

---

public static class Extensions
{
    public static IEnumerable<string> MyReadLines(this FileStream f)
    {
        var sr = new StreamReader(f);
        var line = sr.ReadLine();
        while (line != null)
        {
            yield return line;
            line = sr.ReadLine();
        }
    }
    public static void MyWriteLines(this FileStream f, IEnumerable<string> lines)
    {
        var sw = new StreamWriter(f);
        foreach(var line in lines)
        {
            sw.WriteLine(line);
        }
    }
}