Question

我正在开发一个可视化的基本应用程序，它连接到名为Trips的微软访问数据库。它记录了一个人的商务和休闲旅行。用户应该能够显示商务和休闲旅行的总数，所有旅行以及从特定来源到特定目的地的旅行次数。最后一部分是我遇到麻烦的地方。当我在单选按钮选择后单击btn_Trips时，它会使用所选原点或所选目标拉出所有行，而不是拉动仅包含该特定原点和目标的行，然后显示计数。我不知道如何解决这个问题，所以非常感谢任何帮助。感谢

选项明确开启选项严格打开选项推断关闭

公共类frmMain

Private Sub frmMain_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    'TODO: This line of code loads data into the 'TripsDataSet.tblTrips' table. You can move, or remove it, as needed.
    Me.TblTripsTableAdapter.Fill(Me.TripsDataSet.tblTrips)
End Sub

Private Sub btnExit_Click(sender As Object, e As EventArgs) Handles btnExit.Click
    Me.Close()
End Sub

Private Sub btnAll_Click(sender As Object, e As EventArgs) Handles btnAll.Click
    'displays all trips
    Me.TblTripsTableAdapter.Fill(Me.TripsDataSet.tblTrips)
    TblTripsDataGridView.DataSource = TripsDataSet.tblTrips
End Sub


Private Sub btnCount_Click(sender As Object, e As EventArgs) Handles btnCount.Click
    'displays either business trips or pleasure trips
    Dim foundRows() As TripsDataSet.tblTripsRow
    Dim businesspleasure As String = ""
    If radBusiness.Checked Then
        businesspleasure = "B"
    ElseIf radPleasure.Checked Then
        businesspleasure = "P"
    End If

    foundRows = CType(Me.TripsDataSet.tblTrips.Select("BusinessPleasure = '" & businesspleasure & "'"), Trips_Project.TripsDataSet.tblTripsRow())

    Dim ds As New TripsDataSet.tblTripsDataTable
    For Each row As DataRow In foundRows
        ds.ImportRow(row)
    Next
    TblTripsDataGridView.DataSource = ds

    MessageBox.Show("Trips:  " & TblTripsDataGridView.RowCount - 1)
End Sub

Private Sub btnTrips_Click(sender As Object, e As EventArgs) Handles btnTrips.Click
    Dim foundOrigin() As TripsDataSet.tblTripsRow
    Dim foundDestin() As TripsDataSet.tblTripsRow
    Dim originTrip As String
    Dim destinTrip As String

    If radOrAtl.Checked Then
        originTrip = "Atlanta"
    ElseIf radOrChi.Checked Then
        originTrip = "Chicago"
    ElseIf radOrLa.Checked Then
        originTrip = "Los Angeles"
    Else
        originTrip = "Nashville"
    End If
    foundOrigin = CType(Me.TripsDataSet.tblTrips.Select("Origin = '" & originTrip & "'"), Trips_Project.TripsDataSet.tblTripsRow())

    If radDestAtl.Checked Then
        destinTrip = "Atlanta"
    ElseIf radDestChi.Checked Then
        destinTrip = "Chicago"
    ElseIf radDestLa.Checked Then
        destinTrip = "Los Angeles"
    Else
        destinTrip = "Nashville"
    End If
    foundDestin = CType(Me.TripsDataSet.tblTrips.Select("Destination = '" & destinTrip & "'"), Trips_Project.TripsDataSet.tblTripsRow())

    Dim ds As New TripsDataSet.tblTripsDataTable
    For Each row As DataRow In foundOrigin
        ds.ImportRow(row)
    Next
    For Each row As DataRow In foundDestin
        ds.ImportRow(row)
    Next
    TblTripsDataGridView.DataSource = ds

    MessageBox.Show("Total Trips:  " & TblTripsDataGridView.RowCount - 1)
End Sub

结束班

Answer 1

看看Linq以及您可以使用的不同方法。我不知道你想要最终得到什么，但如果我正确解释你的解释你只想要这些行的计数。您应该能够将linq（请参阅this page）与数据表一起使用，所以：

Dim query =
    from row in Me.TripsDataSet.tblTripsDataTable
    where row.Origin = originTrip and row.Destination = destinTrip
    select row

MessageBox.Show(String.Format("Total Trips: {0}", query.Count())

Answer 2

你的问题在这里：

....
foundOrigin = CType(Me.TripsDataSet.tblTrips.Select("Origin = '" & originTrip & "'"), Trips_Project.TripsDataSet.tblTripsRow())

....
foundDestin = CType(Me.TripsDataSet.tblTrips.Select("Destination = '" & destinTrip & "'"), Trips_Project.TripsDataSet.tblTripsRow())

您在一个阵列上选择具有所选原点的行程，并在另一个阵列上与所选目的地一起跳闸。您可以使用AND在一个句子中选择两者：

If radOrAtl.Checked Then
    originTrip = "Atlanta"
ElseIf radOrChi.Checked Then
    originTrip = "Chicago"
ElseIf radOrLa.Checked Then
    originTrip = "Los Angeles"
Else
    originTrip = "Nashville"
End If

If radDestAtl.Checked Then
    destinTrip = "Atlanta"
ElseIf radDestChi.Checked Then
    destinTrip = "Chicago"
ElseIf radDestLa.Checked Then
    destinTrip = "Los Angeles"
Else
    destinTrip = "Nashville"
End If
foundTrips = CType(Me.TripsDataSet.tblTrips.Select(String.Format("Origin = '{0}' AND Destination = '{1}'", originTrip, destinTrip)), Trips_Project.TripsDataSet.tblTripsRow())

我还建议在连接多个字符串时使用String.Format。

另一个选项是LINQ，如另一个答案中所述，但IMO是一种矫枉过正，因为这是一个简单的案例，因为数据表已经为您提供了一种灵活的方法来过滤行。

编码用于根据单选按钮选择获取计数的按钮

2 个答案: