问正在尝试将ListBox选定项目的总和从本地DataTable获取到标签中

EN

Dim totalOperationsTime As Double

For Each view As DataRowView In ListBox1.SelectedItems
    totalOperationsTime += CDbl(view("OperationsTime"))
Next

Dim totalOperationsTime = ListBox1.SelectedItems.Cast(Of DataRowView)().
                                                 Sum(Function(view) CDbl(view("OperationsTime")))

Public Class ListBoxEx
    Inherits ListBox

    Public Function GetItemValue(item As Object) As Object
        Dim index = Me.Items.IndexOf(item)

        If (index <> -1 AndAlso Me.DataManager IsNot Nothing) Then
            Return Me.FilterItemOnProperty(Me.DataManager.List(index), Me.ValueMember)
        End If

        Return Nothing
    End Function

End Class

Dim totalOperationsTime As Double

For Each item In ListBoxEx1.SelectedItems
    totalOperationsTime += CDbl(ListBoxEx1.GetItemValue(item))
Next

Dim totalOperationsTime = ListBox1.SelectedItems.Cast(Of Object)().
                                                 Sum(Function(item) CDbl(ListBoxEx1.GetItemValue(item)))

' "Please Select" doesn't work well in the ListBox, I added it as an option
Private Shared Function GetData(ByVal sql As String, insertPleaseSelect As Boolean) As DataTable
    Dim constr As String = "Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Users\hartj\Documents\visual studio 2015\Projects\TIMEMATRIX2.0\TIMEMATRIX2.0\TMX.mdf;Integrated Security=True"
    Using con As SqlConnection = New SqlConnection(constr)
        Using sda As SqlDataAdapter = New SqlDataAdapter(sql, con)
            Dim dt As DataTable = New DataTable()
            sda.Fill(dt)
            If insertPleaseSelect Then
                Dim row As DataRow = dt.NewRow()
                row(0) = 1
                row(1) = "Please Select"
                dt.Rows.InsertAt(row, 0)
            End If
            Return dt
        End Using
    End Using
End Function

Private Sub MainHome_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
    ComboBox1.DataSource = GetData("SELECT  [SizeId], [SizeName] FROM [Size]", True)
    ComboBox1.DisplayMember = "SizeName"
    ComboBox1.ValueMember = "SizeId"
    ComboBox2.Enabled = False
    ListBox1.SelectionMode = SelectionMode.MultiSimple ' allow multi-select
End Sub

Private Sub ComboBox1_SelectionChangeCommitted(sender As Object, e As EventArgs) Handles ComboBox1.SelectionChangeCommitted
    ComboBox2.DataSource = Nothing
    ComboBox2.Enabled = False
    If ComboBox1.SelectedValue.ToString() <> "0" Then
        Dim sql As String = String.Format("SELECT [DetailLevelId], [DetailLevelName] FROM [DetailLevel] WHERE [SizeId] = {0}", ComboBox1.SelectedValue)
        ComboBox2.DataSource = GetData(sql, True)
        ComboBox2.DisplayMember = "DetailLevelName"
        ComboBox2.ValueMember = "DetailLevelId"
        ComboBox2.Enabled = True
    End If
End Sub

Private Sub ComboBox2_SelectionChangeCommitted(sender As Object, e As EventArgs) Handles ComboBox2.SelectionChangeCommitted
    ListBox1.DataSource = Nothing
    ListBox1.Enabled = False
    If ComboBox2.SelectedValue.ToString() <> "0" Then
        Dim sql As String = String.Format("SELECT [OperationsId], [OperationsName], [OperationsTime] FROM [Operations] WHERE [DetailLevelId] = {0}", ComboBox2.SelectedValue)
        ListBox1.DataSource = GetData(sql, False)
        ListBox1.DisplayMember = "OperationsName" ' changed this from ValueMember to DisplayMember
        ListBox1.ValueMember = "OperationsTime"
        ListBox1.Enabled = True
        ListBox1.ClearSelected() ' Every time the ListBox is populated, clear it
    End If
End Sub

' Added this handler to respond to user input, not programmatic selection changes
Private Sub ListBox1_Click(sender As Object, e As EventArgs) Handles ListBox1.Click
    ' Here is the sum
    Label9.Text = ListBox1.SelectedItems.OfType(Of DataRowView).Sum(Function(o) CType(o("OperationsTime"), Double))
End Sub