如何锁定文件，读取其内容并覆盖它？ [复制]

Question

我需要读取文件的内容并在文件被锁定时覆盖它。我不希望文件在读写操作之间被解锁。

using (var file = new FileStream(filePath, FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None))
{
  using (var reader = new StreamReader(file, Encoding.Unicode))
  using (var writer = new StreamWriter(file, Encoding.Unicode))
  {
    // read
    // calculate new content
    // overwrite - how do I do this???
  }
}

如果我使用两个FileStreams，则在实例化写入器时会清除文件，但会在读取器和写入器实例化之间短暂解锁文件。

using (var reader = new StreamReader(new FileStream(filePath, FileMode.OpenOrCreate, FileAccess.Read, FileShare.None)))
{
  // read
  // calculate new content
}

using (var writer = new StreamWriter(new FileStream(filePath, FileMode.Create, FileAccess.Write, FileShare.None)))
{
  // write
}

Answer 1

如果你保持打开原始文件流，你可以这样做：

using (var file = new FileStream(filePath, FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None))
{
   // This overload will leave the underlying stream open
  using (var reader = new StreamReader(file, Encoding.Unicode, true, 4096, true))
  {
      //Read
  }

  file.SetLength(0); //Truncate the file and seek to 0

  using (var writer = new StreamWriter(file, Encoding.Unicode))
  {
        //Write the new data
  }
}