Question

所以我有一个带有菜单栏和lstbox的表单。在菜单栏上是显示选项，有3个选项;所有，小说或非小说。文本文件按顺序包含书名，作者，类别（fic或nonfic），股票，价格。当用户点击全部显示时，我希望所有标题都显示在列表框中。如果他们点击Nonfic，只点击非文字标题，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要显示的小说或非小说书籍标题的代码，以及列表框在每个按钮之间刷新而不是添加到列表框。任何帮助都非常适用！

Answer 1

在此代码中显示数据的最佳方法是将显示代码移动到处理循环中。

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，如果使用.net 3.5或更高版本，则使用LINQ

可能更清晰

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

显示文本文件中的某些项目

1 个答案: