Programmi Visual Basic - prof.Claudio Maccherani

Programmi Visual Basic - prof. Claudio Maccherani - Perugia - 2009
gestione archivi RANDOM (ad accesso diretto) in Visual Basic 2008

applicazione Alunni0Rnd - archivio random Alunni.dat
record ALU:
Matr integer, Nome string_*25, Citta string_*20, Sesso string_*1, Classe string_*4

 '+------------------------------------------------------------------------------------------+
 '| Alunni0Rnd - applicazione VB2008, esempio di gestione Archivi RANDOM                     |
 '|             (Prof.Claudio Maccherani)                                                    |
 '+------------------------------------------------------------------------------------------+

 Imports VB = Microsoft.VisualBasic ' per usare alcune vecchie funzioni Visual Basic 6.0

 Public Class frmAlunniRnd
    ' definisce la struttura del record (si usa VBFixedString perché VB2008 NON ha string*n)
    Structure RecAlu
        Dim Matr As Integer
        <VBFixedString(25)> Dim Nome As String
        <VBFixedString(20)> Dim Citta As String
        <VBFixedString(1)> Dim Sesso As String
        <VBFixedString(4)> Dim Classe As String
    End Structure
    Dim Alu As RecAlu
    Dim File As String = "Alunni.dat", MaxRec As Integer = 20, FilNum As Integer
    ' apre l'archivio al caricamento del form -----------------------------------------------
    Private Sub frmArchRnd_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)
                                Handles MyBase.Load
        FilNum = FreeFile()
        FileOpen(FilNum, File, OpenMode.Random, , , Len(Alu))
        Call Elenco()
    End Sub
    ' creazione iniziale dell'archivio (o suo azzeramento, se esiste) -----------------------
    Private Sub cmdCrea_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
                              Handles cmdCrea.Click
        If MsgBox("CREAZIONE ARCHIVIO: se esiste sarà azzerato. Continuo ?", vbYesNo) = vbYes Then
            Alu.Matr = 0 : Alu.Nome = "" : Alu.Citta = "" : Alu.Sesso = "" : Alu.Classe = ""
            For i = 1 To MaxRec : FilePut(FilNum, Alu, i) : Next
            MsgBox("Archivio creato")
        End If
    End Sub
    ' attiva la finestra di scrittura -------------------------------------------------------
    Private Sub cmdInse_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
                              Handles cmdInse.Click
        Azzera() : cmdReg.Visible = True : cmdLeggi.Visible = False
        panMenu.Visible = False : boxRec.Visible = True
    End Sub
    ' azzeramento text box ------------------------------------------------------------------
    Private Sub Azzera()
        TxtRec.Text = "" : TxtMat.Text = "" : txtNom.Text = "" : txtCit.Text = ""
        txtSex.Text = "" : txtCla.Text = ""
    End Sub
    ' chiude la finestra di gestione (e torna a quella di scelta) ---------------------------
    Private Sub cmdChiudi_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
                                Handles cmdChiudi.Click
        panMenu.Visible = True : boxRec.Visible = False
    End Sub
    ' registra un nuovo record --------------------------------------------------------------
    Private Sub cmdReg_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
                             Handles cmdReg.Click
        Dim rec As Integer, norec As Boolean : rec = 0 : norec = True
        If Len(Trim(TxtRec.Text)) > 0 Then
            rec = CInt(TxtRec.Text)
            If rec > 0 And rec < MaxRec Then
                norec = False
                If MsgBox("Confermi la registrazione del record numero " & rec & " ? ",
                           vbYesNo) = vbYes Then
                    Alu.Matr = CInt(TxtMat.Text)
                    Alu.Nome = txtNom.Text
                    Alu.Citta = txtCit.Text
                    Alu.Sesso = txtSex.Text
                    Alu.Classe = txtCla.Text
                    FilePut(FilNum, Alu, rec)
                    Call Elenco()
                    MsgBox("Record registrato")
                End If
            End If
        End If
        If norec Then MsgBox("Numero Record NON valido !", MsgBoxStyle.Exclamation)
    End Sub
    ' fine prpgramma ------------------------------------------------------------------------
    Private Sub cmdEsci_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
                              Handles cmdEsci.Click
        FileClose(FilNum) : Me.Close()
    End Sub
    ' attiva la finestra di lettura ---------------------------------------------------------
    Private Sub cmdLettura_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
                                 Handles cmdLettura.Click
        Azzera() : cmdReg.Visible = False : cmdLeggi.Visible = True
        panMenu.Visible = False : boxRec.Visible = True
    End Sub
    ' legge il record specificato -----------------------------------------------------------
        Private Sub cmdLeggi_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
                               Handles cmdLeggi.Click
        Dim rec As Integer, norec As Boolean : rec = 0 : norec = True
        If Len(Trim(TxtRec.Text)) > 0 Then
            rec = CInt(TxtRec.Text)
            If rec > 0 And rec < MaxRec Then
                FileGet(FilNum, Alu, rec)
                TxtMat.Text = Alu.Matr
                txtNom.Text = Alu.Nome
                txtCit.Text = Alu.Citta
                txtSex.Text = Alu.Sesso
                txtCla.Text = Alu.Classe
                norec = False
            End If
        End If
        If norec Then MsgBox("Numero Record NON valido !", MsgBoxStyle.Exclamation)
    End Sub
    ' visualizza sulla list box l'elenco degli studenti -------------------------------------
    Private Sub Elenco()
        Dim riga As String : lstA.Items.Clear()
        lstA.Items.Add("n.rec Matr Nome" & Space(16) & " Città" & Space(11) & "Sesso Classe")
        lstA.Items.Add("---------------------------------------------------------------------")
        Alu.Matr = 0 : Alu.Nome = "" : Alu.Citta = "" : Alu.Sesso = "" : Alu.Classe = ""
        For i = 1 To MaxRec
            FileGet(FilNum, Alu, i)
            If Alu.Matr > 0 Then
                riga = "  " & VB.Right(Space(2) & i, 2) & "  " & _
                       VB.Right(Space(4) & Alu.Matr, 4) & " " & _
                       VB.Left(Alu.Nome & Space(20), 20) & " " & _
                       VB.Left(Alu.Citta & Space(20), 15) & "    " & Alu.Sesso & "  " & Alu.Classe
                lstA.Items.Add(riga)
            End If
        Next
    End Sub
 End Class