ArrayList - Text file reader Learn programming Visual Basic (VB.net)



Lesson:

Dynamic Memory Management


Exercise:

ArrayList - Text file reader


Objetive:

provide your basic text file reader here, which displays 21 lines of text and allows the user to navigate using the up and down arrow keys, and exit using the ESC key.

Hints:
The text file reader should have three methods:

ReadFile (reads the text file and stores it in memory)
ShowMenu (clears the console, sets the top and bottom lines of the console [row 23], changes colors using Console.BackgroundColor, Console.ForegroundColor, ConsoleColor and Console.SetCursorPosition(column, row). Once the menu is prepared, remember to set the cursor in the second row).
ShowFrom (writes 21 lines, considering the position of the first line to write)
The main program logic should be as follows: ShowMenu, ShowFrom, ReadKey, ShowMenu, ShowFrom, ReadKey....


Code:

Imports System
Imports System.IO
Imports System.Collections
Namespace LectorTexto
    Class Program
        Shared lista As ArrayList = New ArrayList()
        Shared fin As Boolean
        Shared lineaDesde As Integer = 0, lineaHasta As Integer = 21

        Private Shared Sub Main(ByVal args As String())
            Console.Write("Introduce nombre archivo: ")
            Dim nombreArchivo As String = Console.ReadLine()
            LeerFichero(nombreArchivo)

            Do
                MostrarMenu()
                EscribirLineas(lineaDesde, lineaHasta)
                LeerTecla()
            Loop While Not fin
        End Sub

        Private Shared Sub LeerTecla()
            Dim cki As ConsoleKeyInfo
            cki = Console.ReadKey()

            If cki.Key = ConsoleKey.Escape Then
                fin = True
            ElseIf cki.Key = ConsoleKey.UpArrow Then

                If lineaDesde > 0 Then
                    lineaDesde -= 1
                    lineaHasta -= 1
                End If
            ElseIf cki.Key = ConsoleKey.DownArrow Then

                If lineaHasta < lista.Count Then
                    lineaDesde += 1
                    lineaHasta += 1
                End If
            ElseIf cki.Key = ConsoleKey.PageUp Then

                If (lineaHasta + 21) < lista.Count Then
                    lineaDesde += 21
                    lineaHasta += 21
                Else
                    lineaDesde += lista.Count - lineaHasta
                    lineaHasta += lista.Count - lineaHasta
                End If
            ElseIf cki.Key = ConsoleKey.PageDown Then

                If (lineaDesde - 21) > 0 Then
                    lineaDesde -= 21
                    lineaHasta -= 21
                Else
                    lineaHasta = lineaDesde + (21 - lineaDesde)
                    lineaDesde = 0
                End If
            End If
        End Sub

        Private Shared Sub EscribirLineas(ByVal desde As Integer, ByVal hasta As Integer)
            For i As Integer = desde To hasta - 1
                Console.WriteLine(lista(i))
            Next
        End Sub

        Private Shared Sub MostrarMenu()
            Console.Clear()
            Console.BackgroundColor = ConsoleColor.Cyan
            Console.ForegroundColor = ConsoleColor.Black
            Console.WriteLine("    ==> Lector .txt --- Version 1.0")
            Console.SetCursorPosition(0, 23)
            Console.BackgroundColor = ConsoleColor.Cyan
            Console.ForegroundColor = ConsoleColor.Black
            Console.WriteLine("Pulse ESC para salir, fecha arriba y abajo para mover")
            Console.SetCursorPosition(0, 1)
            Console.BackgroundColor = ConsoleColor.Black
            Console.ForegroundColor = ConsoleColor.White
        End Sub

        Private Shared Sub LeerFichero(ByVal nombreArchivo As String)
            If Not File.Exists(nombreArchivo) Then
                Console.WriteLine("El fichero de texto no existe")
            Else

                Try
                    Dim archivoTexto As StreamReader = File.OpenText(nombreArchivo)
                    Dim line As String

                    Do
                        line = archivoTexto.ReadLine()
                        If line IsNot Nothing Then lista.Add(line)
                    Loop While line IsNot Nothing

                    archivoTexto.Close()
                Catch e As Exception
                    Console.WriteLine("Error, " & e.Message)
                End Try
            End If
        End Sub
    End Class
End Namespace



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