TextStream ReadPreviousLine [英] TextStream ReadPreviousLine

问题描述

你好.

有人可以帮助我阅读上一行吗?

Could somebody help me with reading previous line?

在发布的示例中，我使用StreamReader. ReadNextLine可以.但是用于读取前一行仅在文件开始时可用.如果我深陷文件中，则必须等待10分钟.对于上一行.

In posted example I use StreamReader. It is OK for ReadNextLine. but for reading previous line is usable only on start of file. If I'm deep in the file I have to waiting 10 min. for previous line.

我需要更好的方法.

谢谢.

示例代码

选项显式打开

公共类Form1
    Dim _strFile As String =""
    Dim _Reader As IO.StreamReader = Nothing
   暗_ulngLine为ULong = 0
    Dim _strLine As String =""

Public Class Form1
    Dim _strFile As String = ""
    Dim _Reader As IO.StreamReader = Nothing
    Dim _ulngLine As ULong = 0
    Dim _strLine As String = ""

  私有Sub cmdOpenFile_Click(ByVal发送者作为对象，ByVal e作为System.EventArgs)处理cmdOpenFile.Click
      将fd作为新的System.Windows.Forms.OpenFileDialog

    Private Sub cmdOpenFile_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles cmdOpenFile.Click
        Dim fd As New System.Windows.Forms.OpenFileDialog

       fd.Filter =可以记录文件(* .csv; *.txt)| * .csv; *.txt"
       fd.FilterIndex = 1
       fd.RestoreDirectory = True

        fd.Filter = "Can log files (*.csv;*.txt)|*.csv;*.txt"
        fd.FilterIndex = 1
        fd.RestoreDirectory = True

      如果fd.ShowDialog()= System.Windows.Forms.DialogResult.OK然后

        If fd.ShowDialog() = System.Windows.Forms.DialogResult.OK Then

           _strFile = fd.FileName
           Me.Text = IO.Path.GetFileName(_strFile)
           _Reader =新的IO.StreamReader(_strFile)
          如果不是_Reader.EndOfStream然后
                             _ulngLine = _ulngLine +1
                             _strLine = _Reader.ReadLine
                             frmUpdate()
          如果结束
      其他

            _strFile = fd.FileName
            Me.Text = IO.Path.GetFileName(_strFile)
            _Reader = New IO.StreamReader(_strFile)
            If Not _Reader.EndOfStream Then
                _ulngLine = _ulngLine + 1
                _strLine = _Reader.ReadLine
                frmUpdate()
            End If
        Else

          退出子
      如果结束
   结束

            Exit Sub
        End If
    End Sub

  私人Sub cmdNextLine_Click(按对象发送ByByVal，按System.EventArgs接收ByVal e)处理cmdNextLine.Click
       _ulngLine = _ulngLine +1
       _strLine = _Reader.ReadLine
       frmUpdate()
   结束

    Private Sub cmdNextLine_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles cmdNextLine.Click
        _ulngLine = _ulngLine + 1
        _strLine = _Reader.ReadLine
        frmUpdate()
    End Sub

  私有Sub cmdPreviousLine_Click(ByVal发送者作为对象，ByVal e作为System.EventArgs)处理cmdPreviousLine.Click
      暗淡为ULong = 0
       _Reader.Close()
       _Reader =没什么
       _Reader =新的IO.StreamReader(_strFile)
       _ulngLine = _ulngLine-1

    Private Sub cmdPreviousLine_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles cmdPreviousLine.Click
        Dim ulng As ULong = 0
        _Reader.Close()
        _Reader = Nothing
        _Reader = New IO.StreamReader(_strFile)
        _ulngLine = _ulngLine - 1

      做
           ulng = ulng + 1
           _strLine = _Reader.ReadLine
       ulng<>时循环_ulngLine

        Do
            ulng = ulng + 1
            _strLine = _Reader.ReadLine
        Loop While ulng <> _ulngLine

       frmUpdate()

        frmUpdate()

  结束

    End Sub

  私人子frmUpdate()
       lblLineNumber.Text = _ulngLine
       lblLineText.Text = _strLine

    Private Sub frmUpdate()
        lblLineNumber.Text = _ulngLine
        lblLineText.Text = _strLine

      如果是_Reader.EndOfStream然后
           cmdNextLine.Enabled =假
      其他
           cmdNextLine.Enabled = True
      如果结束

        If _Reader.EndOfStream Then
            cmdNextLine.Enabled = False
        Else
            cmdNextLine.Enabled = True
        End If

      如果_ulngLine< 2然后
           cmdPreviousLine.Enabled =假
      其他
           cmdPreviousLine.Enabled = True
      如果结束

        If _ulngLine < 2 Then
            cmdPreviousLine.Enabled = False
        Else
            cmdPreviousLine.Enabled = True
        End If

  结束

    End Sub

  私有子Form1_Activated(ByVal发送者作为对象，ByVal e作为System.EventArgs)处理Me.Activated
       cmdNextLine.Enabled =假
       cmdPreviousLine.Enabled =假
   结束

    Private Sub Form1_Activated(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Activated
        cmdNextLine.Enabled = False
        cmdPreviousLine.Enabled = False
    End Sub

   私有子Form1_FormClosed(ByVal发送者作为对象，ByVal e作为System.Windows.Forms.FormClosedEventArgs)处理Me.FormClosed
       _Reader.Close()
   结束子
结束类

    Private Sub Form1_FormClosed(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosedEventArgs) Handles Me.FormClosed
        _Reader.Close()
    End Sub
End Class

推荐答案

除非返回到开头，否则无法读取流中的前一行.这就是流的本质.

You can't read the previous line in a stream except by going back to the beginning. That's the nature of streams.

我能想到的两种可能的解决方案:

Two possible solution I can think of:

1读取下一行时，将前一行保存在字段中，并以上一行方法获取它.

1 When the next line is read save the previous one in a field and get that in previous line method.

2使用ReadAllLines将整个文件读入数组并使用它.如果文件太大，则可能无法实现.

2 Use ReadAllLines to read the complete file into an array and use that. May not be possible if the file is extremely large.

第三种方法是使用固定长度的线，并使用搜索"来获取所需的线，但我认为这不可行.

A third method would be to have fixed length lines and use Seek to get the line you want but I don't think that is feasible here.

这篇关于TextStream ReadPreviousLine的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！