visual-studio-2010 - 显示文本文件中的某些项目

Question

所以我有一个带有菜单栏和 lstbox 的表单。菜单栏上是显示选项，有 3 个选项；全部，小说或非小说。文本文件按顺序包含书名、作者、类别（小说或非小说）、库存、价格。当用户单击全部显示时，我希望所有标题都显示在列表框中。如果他们点击非小说，只有非小说标题，与小说相同。到目前为止，这是我的代码：

Private Sub menuDisplay_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles menuDisplay.Click

    Dim books() As String = IO.File.ReadAllLines("Books.txt")
    Dim data() As String
    Dim allBooksTitle, allNonFicTitle, allFicTitle As String

    For i As Integer = 0 To books.Count - 1
        data = books(i).Split(","c)
        allBooksTitle = data(2)
        If data(2).Trim = "N" Then
            allNonFicTitle = data(0)
        ElseIf data(2).Trim = "F" Then
            allFicTitle = data(0)
        End If
    Next

    ' show result
    If menuDisplayAll.Checked Then
        lstBox.Items.Add(allBooksTitle)
    ElseIf menuDisplayFic.Checked Then
        lstBox.Items.Add(allFicTitle)
    ElseIf menuDisplayNonFic.Checked Then
        lstBox.Items.Add(allNonFicTitle)
    End If
End Sub

我不太确定如何编写代码来显示小说或非小说书籍标题以及列表框在每个按钮之间刷新而不是添加到列表框中。非常感谢任何帮助！

Answer 1

在此代码中显示数据的最佳方式是将显示代码移到处理循环中。

Private Sub menuDisplay_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles menuDisplay.Click

    Dim books() As String = IO.File.ReadAllLines("Books.txt")

    lstbox.Items.Clear() 'remove all items from the listbox

    For i As Integer = 0 To books.Count - 1
        Dim data() As String 'Moved inside to limit scope
        Dim allBooksTitle, allNonFicTitle As String

        data = books(i).Split(","c)
        allBooksTitle = data(2) 'store the two fields
        allNonFicTitle = data(0)

        If menuDisplayAll.Checked Then 'check for each item
            lstBox.Items.Add(allBooksTitle)
        ElseIf menuDisplayFic.Checked AndAlso data(2).Trim = "F" Then
            lstBox.Items.Add(allNonFicTitle) 
        ElseIf menuDisplayNonFic.Checked AndAlso data(2).Trim = "N"Then
            lstBox.Items.Add(allNonFicTitle)
        End If
    Next
End Sub

但是，如果您使用 .net 3.5 或更高版本，使用 LINQ 可能会更干净

Private Sub menuDisplay_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles menuDisplay.Click

    Dim books() As String = IO.File.ReadAllLines("Books.txt")

    lstbox.Items.Clear()
    Dim query As IEnumerable(Of String)
    If menuDisplayAll.Checked Then 'check for each item 
            query = From book As String In books let data As String() = book.Split(',') Select data(0)
    ElseIf menuDisplayFic.Checked
            query = From book As String In books let data As String() = book.Split(',')  Where data(2).Trim = "F" Select data(2)
    ElseIf menuDisplayNonFic.Checked
            query = From book As String In books let data As String() = book.Split(',')  Where data(2).Trim = "N" Select data(2)
    End If

    lstBox.Items.AddRange(query)
End Sub