vb.net DataView 将自身更新为新的 rowfilter
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DataView Update itself to the new rowfilter
提问by Tajamul Iqbal
I am trying to retain some rows in dataview for some operations to perform after I get the filtered rows, but the issue is , every time the code runs, the dataview is updated to the filter last applied. Here is the code snippest.
我试图在数据视图中保留一些行，以便在获得过滤后的行后执行某些操作，但问题是，每次代码运行时，数据视图都会更新为上次应用的过滤器。这是代码片段。
If dsEmp.Tables.Count > 0 Then
dvEmp = dsEmp.Tables(0).DefaultView
dvEmp.RowFilter = "IDENTIFICATION_CODE = '" & IDENTIFICATION_CODE & "' and EMPLOYEE_DESC = 'Employment1'"
Dim dv1 As DataView = dvEmp
dvEmp.RowFilter = ""
If dsEmp.Tables(0).Rows.Count > 1 Then
dvEmp2 = New DataView
dvEmp2 = dsEmp.Tables(0).DefaultView
dvEmp2.RowFilter = "IDENTIFICATION_CODE = '" & IDENTIFICATION_CODE & "' and EMPLOYEE_DESC = 'Employment2'"
Dim dv2 As DataView = dvEmp2
dvEmp2.RowFilter = ""
End If
If dsEmp.Tables(0).Rows.Count > 2 Then
dvEmpPrevious = New DataView
dvEmpPrevious = dsEmp.Tables(0).DefaultView
dvEmpPrevious.RowFilter = "IDENTIFICATION_CODE = '" & IDENTIFICATION_CODE & "' and EMPLOYEE_DESC = 'Employment3'"
Dim dv3 As DataView = dvEmpPrevious
dvEmpPrevious.RowFilter = ""
End If
End If
but when I check the value of dv1, after second filter, it has the different values in it.
但是当我检查 dv1 的值时，在第二个过滤器之后，它有不同的值。
Could any one give some solution. Thanks
任何人都可以提供一些解决方案。谢谢
采纳答案by Steve
You are just changing the name of the variables but every DataView above is still referencing the same DataView (the DefaultView of the table). So when you reset the RowFilter you apply this change to the DefaultView as well.
您只是更改了变量的名称，但上面的每个 DataView 仍然引用相同的 DataView（表的 DefaultView）。因此，当您重置 RowFilter 时，您也会将此更改应用于 DefaultView。
If you want to have different views with different filters then you need to create a DataView passing the source DataTable
如果你想拥有不同过滤器的不同视图，那么你需要创建一个传递源 DataTable 的 DataView
dvEmp = new DataView(dsEmp.Tables(0))
dvEmp.RowFilter = "IDENTIFICATION_CODE = '" & IDENTIFICATION_CODE & "' and EMPLOYEE_DESC = 'Employment1'"
Now the dvEmp is no more referencing the DefaultView of the DataTable and it should maintain the correct RowFilter applied
现在 dvEmp 不再引用 DataTable 的 DefaultView，它应该保持应用正确的 RowFilter
Of course, you should use the filtered DataView to test the number of records present in the DataView after the filter not the DataTable.
The DataTable will contain always the same number of records
当然，您应该使用过滤后的 DataView 来测试过滤后 DataView 中存在的记录数，而不是 DataTable。
DataTable 将始终包含相同数量的记录
If dvEmp.Count > 1 Then
.....
