streamreader 未定义

Imports System
        Imports
        Public Class filedemotext
        Dim myfilename As String = "c:\file.txt"
        If file.exists(myfilename) Then
            file.delete(myfilename)
        End If
        Dim sw As streamwriter = file.createtext(myfilename) '创建FILE.txt用于写数据
        sw.writeline("file ")
        sw.writeline("write ")
        sw.writeline("string!")
        sw.flush()     '将缓冲的数据写入基础流
        sw.close()
        Try
            Dim sr As streamreader = file.opentext(myfilename) '打开FILE.TXT用于读数据
            Dim inputstring As String
            inputstring = sr.readline()
            While Not inputstring Is Nothing '检测不到文件尾时打印读出的结果
                Console.WriteLine(inputstring)
                inputstring = sr.readline()
            End While
            sr.close()
        Catch error_info As Exception
            Console.WriteLine("文件操作错误!" & error_info.ToString())
        End Try

我运行后，有7处出错（下划线）Imports语法错误，streamreader未定义类型，class关键字作为标识符无效，file 未声明名称  请问怎么解决？？？？？？？？？？？？