主题：老师，通过for each 集合 去修改这个集合要怎么做？

For Each dr2 As DataRow In drs
            For Each tx As String In txm
                If dr2.lines("药品类别").Contains(tx) = False Then
                    drs.Remove(dr2)
                    Exit For
                End If
            Next
        Next

运行到这段就提示集合已修改。

Dim i As Integer
Dim lb As new List(of String)
Dim drs As new List(of DataRow)
If e.Form.Controls("TextBox1").text = "" Then
    e.Form.Controls("TextBox1").text = e.sender.text
Else
    e.Form.Controls("TextBox1").text = e.Form.Controls("TextBox1").text  & vbcrlf & e.sender.text
End If
For i = 1 To 15
    e.Form.Controls("" & i & "").text = ""
Next
Dim txm As new List(of String)
If e.Form.Controls("GroupBox1").text = "选择药品属性" Then
    For Each tx As String In e.Form.Controls("TextBox1").lines
        txm.add(tx)
    Next
    For Each dr As DataRow In DataTables("兽药品种库").DataRows
        If dr.lines("药品类别").contains(txm(0))= True Then
            drs.add(dr)
        End If
    Next
    If txm.count > 1 Then
        For i = drs.count-1 To 0 Step -1
            For Each tx As String In txm
                If drs(i).lines("药品类别").Contains(tx) = False Then
                    drs.Removeat(i)
                End If
            Next
        Next
    End If
    For Each dr3 As DataRow In drs
        For Each drm As String In dr3.lines("药品类别")
            If txm.contains(drm) = False AndAlso lb.contains(drm) = False Then
                lb.add(drm)
            End If
        Next
    Next

额就是一个递进 的 find 选项。  但是我的  row 的内容是分行的。