Question

我有以下代码：

Public Class Form1
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    ListBox1.Items.Add("Celsius to Farenheit")
    ListBox1.Items.Add("Farenheit to Celsius")

End Sub

Private Sub ListBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
    ' Get the currently selected item in the list box. 
    Dim currentItem As String = ListBox1.SelectedItem.ToString()

    ' Get the currently selected index of the item in the list box.
    Dim currentIndex As Integer = ListBox1.FindString(currentItem)
End Sub

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click ' calculate button
    If String.IsNullOrEmpty(TextBox1.Text) Then
        MsgBox("Please enter a temperature to convert!")
    ElseIf currentItem = "Celsius to Farenheit" Then
        'do celsius to farenheit conversion
    ElseIf currentItem = "Farenheit to Celsius" Then
        'do farenheit to celsius conversion
    Else
        MsgBox("Please select a conversion first!")
    End If
End Sub
End Class

我正在尝试检查，以便在ListBox1中进行特定选择，然后在单击Button1时执行该特定转换。但是，上面的代码不能抛出错误“currentItem未声明。它的保护级别可能无法访问”。我怀疑这与

有关

ListBox1_SelectedIndexChanged

成为私人子公司，但将其改为公开似乎没有任何影响。

有人能指出我正确的方向吗？

感谢。

Answer 1

以下是如何使用SelectedIndexChanged事件捕获用户更改所选列表框项目的索引：

Private Sub ListBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
   ' Get the currently selected item in the list box. 
   Dim currentItem As String = ListBox1.SelectedItem.ToString()

   ' Get the currently selected index of the item in the list box.
   Dim currentIndex As Integer = ListBox1.FindString(currentItem)
End Sub

注意：要自动连接事件，请双击表单设计器中的列表框，它应自动生成Private Sub ListBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged存根方法。

更新：

要使用SelectedIndexChanged事件中收集的值，您必须在类级别（Form1）声明这些变量，以下是此代码：

Public Class Form1
    Dim currentItem As String
    Dim currentIndex As Integer

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        ListBox1.Items.Add("Celsius to Farenheit")
        ListBox1.Items.Add("Farenheit to Celsius")
    End Sub

    Private Sub ListBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
        ' Get the currently selected item in the list box. 
        currentItem = ListBox1.SelectedItem.ToString()

        ' Get the currently selected index of the item in the list box.
        currentIndex = ListBox1.FindString(currentItem)
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click ' calculate button
        If String.IsNullOrEmpty(TextBox1.Text) Then
            MsgBox("Please enter a temperature to convert!")
        ElseIf currentItem = "Celsius to Farenheit" Then
            ' do celsius to farenheit conversion
        ElseIf currentItem = "Farenheit to Celsius" Then
            'do farenheit to celsius conversion
        Else
            MsgBox("Please select a conversion first!")
        End If
   End Sub
End Class

Answer 2

感谢Karl Anderson，我使用以下代码解决了我的问题。

Public Class Form1
Dim currentItem As String
Dim currentIndex As Integer

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    ListBox1.Items.Add("Celsius to Farenheit")
    ListBox1.Items.Add("Farenheit to Celsius")

End Sub

Private Sub ListBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
    ' Get the currently selected item in the list box. 
    currentItem = ListBox1.SelectedItem.ToString()

    ' Get the currently selected index of the item in the list box.
   currentIndex = ListBox1.FindString(currentItem)
End Sub

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click ' calculate button
    If String.IsNullOrEmpty(TextBox1.Text) Then
        MsgBox("Please enter a temperature to convert!")
    ElseIf currentIndex = 0 Then
        Label2.Text = TextBox1.Text & " Celsius = " & (TextBox1.Text * 1.8) + 32 & " Farenheit"
    ElseIf currentIndex = 1 Then
        Label2.Text = TextBox1.Text & " Farenheit = " & (TextBox1.Text - 32) / 1.8 & " Celsius"
    Else
        MsgBox("Please select a conversion first!")
    End If
End Sub
End Class

如何检查何时选择列表项，然后执行某些操作？

2 个答案: