vb.net 根据前两个组合框中的选定项目更改组合框选项

Question

我正在创建一个程序，有人可以将搜索输入到文本框中，然后使用一系列组合框（或仅使用组合框搜索所有内容）缩小结果范围。

程序如下所示：form 1

我已使用以下代码更改了第二个组合框中的选项：

Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.SelectedIndexChanged
    Dim type As String = ComboBox1.SelectedItem
    Dim make As String = ComboBox2.SelectedItem
    Dim model As String = ComboBox3.SelectedItem
    Dim version As String = TextBox2.Text
    Dim memory As String = TextBox3.Text
    Dim problem As String = TextBox4.Text
    Dim casenumber As Integer = Int(Rnd() * 9999) + 1000
    If type = "Phone" Then
        ComboBox2.Items.Clear()
        Dim file As New System.IO.StreamReader("E: \phone.txt")
        For i = 1 To 20
            q(i) = file.ReadLine() & vbNewLine
            ComboBox2.Items.Add(q(i))
        Next
    ElseIf type = "Tablet" Then
        ComboBox2.Items.Clear()
        Dim file As New System.IO.StreamReader("E:\tablet.txt")
        For i = 1 To 20
            q(i) = file.ReadLine() & vbNewLine
            ComboBox2.Items.Add(q(i))
        Next
    ElseIf type = "Desktop computer" Then
        ComboBox2.Items.Clear()
        Dim file As New System.IO.StreamReader("E:\pc.txt")
        For i = 1 To 20
            q(i) = file.ReadLine() & vbNewLine
            ComboBox2.Items.Add(q(i))
        Next
    ElseIf type = "Laptop" Then
        ComboBox2.Items.Clear()
        Dim file As New System.IO.StreamReader("E:\laptop.txt")
        For i = 1 To 20
            q(i) = file.ReadLine() & vbNewLine
            ComboBox2.Items.Add(q(i))
        Next
        'Else
        'Dim objwriter As System.IO.StreamWriter
        'objwriter = My.Computer.FileSystem.OpenTextFileWriter("E:\unknown.txt", True)
        'File.AppendText("type:" And ComboBox1.Text And "make" & ComboBox2.Text And "model: " & ComboBox3.Text And "version: " And TextBox2.Text & "memory" And TextBox3.Text)
    End If
End Sub

但是，该代码无法更改第三个框中的内容。我为每个选项重复了以下代码：

Private Sub ComboBox2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox3.SelectedIndexChanged
    Dim type As String = ComboBox1.SelectedItem
    Dim make As String = ComboBox2.SelectedItem
    Dim model As String = ComboBox3.SelectedItem
    Dim version As String = TextBox2.Text
    Dim memory As String = TextBox3.Text
    Dim problem As String = TextBox4.Text
    If type = "Phone" Then
        If make = "apple" Then
            ComboBox2.Items.Clear()
            Dim file As New System.IO.StreamReader("E:\apple.txt")
            For i = 1 To 20
                q(i) = file.ReadLine() & vbNewLine
                ComboBox3.Items.Add(q(i))
            Next
        ElseIf make = "samsung" Then
            ComboBox2.Items.Clear()
            Dim file As New System.IO.StreamReader("E:\samsung.txt")
            For i = 1 To 20
                q(i) = file.ReadLine() & vbNewLine
                ComboBox3.Items.Add(q(i))
            Next
        ElseIf make = "htc" Then
            ComboBox2.Items.Clear()
            Dim file As New System.IO.StreamReader("E:\htc.txt")
            For i = 1 To 20
                q(i) = file.ReadLine() & vbNewLine
                ComboBox3.Items.Add(q(i))
            Next
        ElseIf make = "Nokia" Then
            ComboBox2.Items.Clear()
            Dim file As New System.IO.StreamReader("E:\Nokia.txt")
            For i = 1 To 20
                q(i) = file.ReadLine() & vbNewLine
                ComboBox3.Items.Add(q(i))
            Next
        ElseIf make = "Blackberry" Then
            ComboBox2.Items.Clear()
            Dim file As New System.IO.StreamReader("E:\blackberry.txt")
            For i = 1 To 20
                q(i) = file.ReadLine() & vbNewLine
                ComboBox3.Items.Add(q(i))
            Next

我已经检查了一些明显的问题，例如输入错误的文本文件名和大写字母等，但无论我做什么都无法让它工作。

有谁知道为什么即使同时满足两个条件（combobox1 和 2 都选择了正确的东西）第三个组合框仍然空白？任何建议将不胜感激。

Answer 1

首先我怀疑这段代码：-

Dim type As String = ComboBox1.SelectedItem.ToString
Dim make As String = ComboBox2.SelectedItem.ToString
Dim model As String = ComboBox3.SelectedItem.ToString
Dim version As String = TextBox2.Text
Dim memory As String = TextBox3.Text
Dim problem As String = TextBox4.Text

如果你的事件不应该出现在每个事件中。它们真的应该放置在所有信息都选择后执行的地方吗？

开始将其粘贴到名为“device type.txt”的文本文件中

电话，E:\phone.txt
平板电脑,E:\tablet.txt
台式电脑,E:\pc.txt
笔记本电脑,E:\laptop.txt

然后编辑您的phones.txt 文件和上述文件的其余部分以匹配该格式，例如这个phone.txt 文件

苹果，E:\apple.txt
三星,E:\samsung.txt
Htc,E:\htc.txt
诺基亚,E\nokia.txt
黑莓,E:\blackberry.txt

对于链接到另一个文件的每个项目，依此类推。对于树中的最后一个文件——我认为这些文件包含每个品牌手机的型号列表，只需将它们保留为一个简单的列表。每个模型后面都没有逗号或其他任何内容。

使用此代码填充每个 ComboBox

Private Sub PopulateComboBox(ByRef cboBox As ComboBox, ByVal itemSource As String)
    RemoveHandler ComboBox1.SelectedIndexChanged, AddressOf ComboBox1_SelectedIndexChanged
    RemoveHandler ComboBox2.SelectedIndexChanged, AddressOf ComboBox2_SelectedIndexChanged
    RemoveHandler ComboBox3.SelectedIndexChanged, AddressOf ComboBox3_SelectedIndexChanged
    Dim devices As New List(Of item)
    Dim csvFlag As Boolean = False
    cboBox.Items.Clear()
    Using MyReader As New Microsoft.VisualBasic.
        FileIO.TextFieldParser(itemSource)
        If MyReader.ReadLine.Contains(",") Then csvFlag = True
    End Using

    Using MyReader As New Microsoft.VisualBasic.
        FileIO.TextFieldParser(itemSource)
        If csvFlag Then
            MyReader.TextFieldType = FileIO.FieldType.Delimited
            MyReader.SetDelimiters(",")
        End If
        Dim currentRow As String() = {"", ""}
        While Not MyReader.EndOfData
            Try
                If csvFlag Then
                    currentRow = MyReader.ReadFields()
                    Dim tempItem As New item
                    tempItem.item = currentRow(0)
                    tempItem.fileName = currentRow(1)
                    devices.Add(tempItem)
                Else
                    currentRow(0) = MyReader.ReadLine
                    Dim tempItem As New item
                    tempItem.item = currentRow(0)
                    tempItem.fileName = ""
                    devices.Add(tempItem)
                End If

            Catch ex As Microsoft.VisualBasic.
              FileIO.MalformedLineException
                MsgBox("Line " & ex.Message & "is not valid and will be skipped.")
            End Try
        End While
    End Using
    If csvFlag Then
        cboBox.DataSource = devices
    cboBox.DisplayMember = "item"
        cboBox.ValueMember = "fileName"
    Else
        cboBox.DataSource = devices
        cboBox.DisplayMember = "item"
        cboBox.ValueMember = "item"
    End If
    AddHandler ComboBox1.SelectedIndexChanged, AddressOf ComboBox1_SelectedIndexChanged
    AddHandler ComboBox2.SelectedIndexChanged, AddressOf ComboBox2_SelectedIndexChanged
    AddHandler ComboBox3.SelectedIndexChanged, AddressOf ComboBox3_SelectedIndexChanged
End Sub

它首先检查正在读取的文件是否是逗号分隔的文件。

如果它被分隔，它将读取 itemSource 中引用的文件并期望一对值。第一个值是您在框中看到的内容（DisplayMember），第二个值是单击框实际返回的内容（ValueMember）

如果文件不是逗号分隔的，它只会读取每一行并将其添加到组合框中，以便正常运行（这对于树中的最后一个文件很重要）

接下来你需要为 ComboBoxes 提供这些方法

Private Sub PopulateComboBox1()
    PopulateComboBox(ComboBox1, "E:\device type.txt")
End Sub

Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.SelectedIndexChanged
    PopulateComboBox(ComboBox2, ComboBox1.SelectedValue.ToString)
End Sub

Private Sub ComboBox2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox2.SelectedIndexChanged
    PopulateComboBox(ComboBox3, ComboBox2.SelectedValue.ToString)
End Sub

Private Sub ComboBox3_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox3.SelectedIndexChanged
    PopulateComboBox(ComboBox3, ComboBox2.SelectedValue.ToString)
End Sub

可能在表单的加载事件中调用填充 Combobox1 的方法。