你的XML文件怎么存发都不是问题，
读取XML的就不在这里写了，我提供一下后续的数据处理，类名XMLMsg内容如下：
Public Class XMLMsg
Public Property Level() As String
Public Property Index() As String
Public Property Code() As String
Public Property Name() As String
End Class
第一步，全局变量三个：
Dim MsgLsit As New List(Of XMLMsg)
Dim Com1 As New List(Of XMLMsg)
Dim Com2 As New List(Of XMLMsg)
Dim Com3 As New List(Of XMLMsg)
第二步，在窗口加载的时候你是读XML，我就不读取了，在Load事件如下代码如下：
Dim tCond As New XMLMsg
tCond.Level = "0"
tCond.Index = "0"
tCond.Code = "A"
tCond.Name = "方案1"
MsgLsit.Add(tCond)
tCond = New XMLMsg
tCond.Level = "1"
tCond.Index = "0"
tCond.Code = "A1"
tCond.Name = "1-默认配置1"
MsgLsit.Add(tCond)
tCond = New XMLMsg
tCond.Level = "2"
tCond.Index = "0"
tCond.Code = "A1A"
tCond.Name = "1-声音1"
MsgLsit.Add(tCond)
tCond = New XMLMsg
tCond.Level = "2"
tCond.Index = "1"
tCond.Code = "A1B"
tCond.Name = "1-回音1"
MsgLsit.Add(tCond)
tCond = New XMLMsg
tCond.Level = "1"
tCond.Index = "1"
tCond.Code = "A2"
tCond.Name = "1-默认配置2"
MsgLsit.Add(tCond)
tCond = New XMLMsg
tCond.Level = "2"
tCond.Index = "0"
tCond.Code = "A2A"
tCond.Name = "1-声音2"
MsgLsit.Add(tCond)
tCond = New XMLMsg
tCond.Level = "2"
tCond.Index = "1"
tCond.Code = "A2B"
tCond.Name = "1-回音2"
MsgLsit.Add(tCond)
tCond = New XMLMsg
tCond.Level = "0"
tCond.Index = "1"
tCond.Code = "B"
tCond.Name = "方案2"
MsgLsit.Add(tCond)
tCond = New XMLMsg
tCond.Level = "1"
tCond.Index = "0"
tCond.Code = "B1"
tCond.Name = "2-默认配置1"
MsgLsit.Add(tCond)
tCond = New XMLMsg
tCond.Level = "2"
tCond.Index = "0"
tCond.Code = "B1A"
tCond.Name = "2-声音1"
MsgLsit.Add(tCond)
tCond = New XMLMsg
tCond.Level = "2"
tCond.Index = "1"
tCond.Code = "B1B"
tCond.Name = "2-回音1"
MsgLsit.Add(tCond)
tCond = New XMLMsg
tCond.Level = "1"
tCond.Index = "1"
tCond.Code = "B2"
tCond.Name = "2-默认配置2"
MsgLsit.Add(tCond)
tCond = New XMLMsg
tCond.Level = "2"
tCond.Index = "0"
tCond.Code = "B2A"
tCond.Name = "2-声音2"
MsgLsit.Add(tCond)
tCond = New XMLMsg
tCond.Level = "2"
tCond.Index = "1"
tCond.Code = "B2B"
tCond.Name = "2-回音2"
MsgLsit.Add(tCond)
ComboBox1.Items.Clear()
Com1.Clear()
Dim Comd1 = From x In MsgLsit Where x.Code = "A" Or x.Code = "B" Select x
For Each t As XMLMsg In Comd1
Com1.Add(t)
ComboBox1.Items.Add(t.Name)
Next
If ComboBox1.Items.Count > 0 Then
ComboBox1.SelectedIndex = 0
End If
然后是二个SelectedIndexChanged事件
代码如下：
Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.SelectedIndexChanged
If ComboBox1.SelectedIndex >= 0 Then
Com2.Clear()
ComboBox2.Items.Clear()
Dim tCond As New XMLMsg
tCond = Com1(ComboBox1.SelectedIndex)
Dim Comd2 = From x In MsgLsit Where x.Level = 1 And x.Code.Substring(0, 1) = tCond.Code Select x
For Each t As XMLMsg In Comd2
Com2.Add(t)
ComboBox2.Items.Add(t.Name)
Next
If ComboBox2.Items.Count > 0 Then
ComboBox2.SelectedIndex = 0
End If
End If
End Sub
Private Sub ComboBox2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox2.SelectedIndexChanged
If ComboBox2.SelectedIndex >= 0 Then
Com3.Clear()
ComboBox3.Items.Clear()
Dim tCond As New XMLMsg
tCond = Com2(ComboBox2.SelectedIndex)
Dim Comd2 = From x In MsgLsit Where x.Level = 2 Select x
For Each t As XMLMsg In Comd2
If t.Code.Substring(0, 2) = tCond.Code Then
Com3.Add(t)
ComboBox3.Items.Add(t.Name)
End If
Next
If ComboBox3.Items.Count > 0 Then
ComboBox3.SelectedIndex = 0
End If
End If
End Sub
效果如下图，你选择了方案2，只会出现方案2的内容，不会出现方案1的，我这里在代码上面，把都加了“1-”和“2”，这样可以把方案1和方案2的子项区分开。
最后说一句，VB.NET决对支持linq，VB.net 你做不到，是你没有用对，如果让你纠结，建议你早点换语言。
