3

我想以小块复制文件（如果需要取消复制操作）。

我正在尝试遵循此处未标记的解决方案：如何复制具有取消复制功能的文件？

但我得到一个 0 字节的文件

我做错了什么？

Public Class Form1

   Dim cancelled As Boolean = Nothing
   Dim input = New System.IO.FileStream("C:\1.txt", System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.Read)
   Dim output = New System.IO.FileStream("C:\Nueva carpeta\1.txt", System.IO.FileMode.CreateNew, System.IO.FileAccess.Write, System.IO.FileShare.Write)

   Public Sub CopyStream(ByVal inputStream As System.IO.Stream, ByVal outputStream As System.IO.Stream)
       'Dim buffer = System.IO.File.ReadAllBytes("C:\1.txt")

       Dim buffer = New Byte((1024) - 1) {}
       Dim bytesRead As Integer = 1

       While (inputStream.Read(buffer, 0, buffer.Length) > 0)
           outputStream.Write(buffer, 0, bytesRead)
           'bytesRead += 1

           If cancelled Then
               MsgBox("operacion cancelada")
               Return
           End If
       End While

       inputStream.Close()
       outputStream.Close()
       MsgBox("operacion terminada")

   End Sub

   Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
       CopyStream(input, output)
   End Sub

End Class

**

更新 1：

**

我尝试按照 Virtlink answer 的步骤将缺失的部分放入我的原始代码中，但我仍然得到一个零字节文件。

> Public Class Form1

    Dim input = New System.IO.FileStream("C:\Test.txt", System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.Read)
    Dim output = New System.IO.FileStream("C:\Test_New.txt", System.IO.FileMode.CreateNew, System.IO.FileAccess.Write, System.IO.FileShare.Write)

    Public Sub CopyStream(ByVal inputStream As System.IO.Stream, ByVal outputStream As System.IO.Stream)

        Dim buffer = New Byte(1024) {}
        Dim bytesRead As Integer

        ' Read some bytes
        While (bytesRead = inputStream.Read(buffer, 0, buffer.Length) > 0)
            ' Write them to the output
            outputStream.Write(buffer, 0, bytesRead)
        End While

    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        CopyStream(input, output)
    End Sub

End Class

**

更新 2：

**

我最近失败的尝试：

    Public Class Form1

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

        Dim input_filepath As String = "C:\Test.txt", output_filepath As String = "C:\Test_New.txt"

        Dim input = New System.IO.FileStream(input_filepath, System.IO.FileMode.Open, System.IO.FileAccess.ReadWrite)
        Dim output = New System.IO.FileStream(output_filepath, System.IO.FileMode.Create, System.IO.FileAccess.ReadWrite)

        CopyStream(input, output)

        ' For Testing:
        If New IO.FileInfo(output_filepath).Length = 0 Then IO.File.Delete(output_filepath) : Application.Exit() Else Process.Start("Notepad", output_filepath)

    End Sub

    Public Sub CopyStream(ByVal inputStream As System.IO.Stream, ByVal outputStream As System.IO.Stream)

        Dim buffer = New Byte(1024) {}, bytesRead As Integer

        While ((bytesRead = inputStream.Read(buffer, 0, buffer.Length)) > 0)
            outputStream.Write(buffer, 0, bytesRead)
        End While

        inputStream.Flush() : outputStream.Flush()
        inputStream.Close() : outputStream.Close()

    End Sub

End Class

**

更新 3：

**

解决方案

问题出在 VB.NET 中，我无法在循环条件中为变量赋值，所以这是工作 Sub：

  Public Sub CopyStream(ByVal inputStream As Stream, ByVal outputStream As Stream)

    Dim buffer = New Byte(1025) {}
    Dim bytesRead As Integer = 0

    Do
        bytesRead = inputStream.Read(buffer, 0, buffer.Length)
        If bytesRead > 0 Then
            outputStream.Write(buffer, 0, bytesRead)
        End If
    Loop While (bytesRead > 0)

    outputStream.Flush()
    inputStream.Close() : outputStream.Close()

End Sub
4

1 回答 1

7

你必须了解你在做什么以及它是如何工作的。

首先，您分配一个缓冲区。

Dim buffer = New Byte(1024) {}

然后你去从输入流中读取一些数据。数据被放入buffer, 从0, 最多buffer.Length字节开始。该方法返回它实际读取并放入缓冲区的字节数。

bytesRead = inputStream.Read(buffer, 0, buffer.Length)

如果您读取的字节数大于 0，那么您还没有到达文件末尾。

While (bytesRead > 0)

然后，您将读取的那些字节（bytesRead字节）准确地写入输出流。从 写入字节buffer，从索引开始0并写入bytesRead字节数。

outputStream.Write(buffer, 0, bytesRead)

由于出于效率原因，流将缓冲您编写的内容，因此您必须刷新并关闭输出流。

outputStream.Flush()
outputStream.Close()

把它放在一起：

Dim buffer = New Byte(1024) {}
Dim bytesRead As Integer

' Read some bytes
While ((bytesRead = inputStream.Read(buffer, 0, buffer.Length)) > 0)
    ' Write them to the output
    outputStream.Write(buffer, 0, bytesRead)

    If cancelled Then
        MsgBox("operacion cancelada")
        Return
    End If

    ' Repeat
End

outputStream.Flush()
outputStream.Close()

上一次写VB是十多年前的事了。您必须确保语法正确。

注意原始代码如何包含这一行： 

While ((bytesRead = inputStream.Read(buffer, 0, buffer.Length)) > 0)

你看到那个bytesRead =部分了吗？您还没有将其复制到您的代码中。必须存储读取的字节数。

最终代码：这适用于我的电脑：

Imports System
Imports System.IO

Namespace ConsoleApplication1
    Friend Class Program
        Private Shared Sub Main(args As String())
            Program.CopyMyFiles()
            Console.WriteLine("DONE!")
            Console.ReadLine()
        End Sub

        Private Shared Sub CopyMyFiles()
            Dim input_filepath As String = "Test.txt"
            Dim output_filepath As String = "Test_New.txt"
            Dim input As FileStream = New FileStream(input_filepath, FileMode.Open, FileAccess.ReadWrite)
            Dim output As FileStream = New FileStream(output_filepath, FileMode.Create, FileAccess.ReadWrite)
            Program.CopyStream(input, output)
        End Sub

        Public Shared Sub CopyStream(inputStream As Stream, outputStream As Stream)
            Dim buffer As Byte() = New Byte(1025)
            Dim bytesRead As Integer
            bytesRead = inputStream.Read(buffer, 0, buffer.Length)
            While bytesRead > 0
                outputStream.Write(buffer, 0, bytesRead)
                bytesRead = inputStream.Read(buffer, 0, buffer.Length)
            End While
            outputStream.Flush()
            inputStream.Close()
            outputStream.Close()
        End Sub
    End Class
End Namespace
于 2013-03-22T01:45:37.167 回答