Sorting DataGridView causes problems

[chris1028]

Hello Xtreme - my first post: please be kind.

 

My application has a read-only datagridview dgvFound fed from a datatable dtFound. This datagridview is permanently displayed whilst the application is running.

 

dtFound is declared public in a module (and exists whilst the application is running).

 

dtFound is fed from any one of around thirty different "finders" that are grouped in three user controls - these finders run sprocs on MSSQL2005 and clear/refill dtFound.

 

Everything works perfectly with dgvFound refreshing nicely in the main form when one of the finders raises a dtFoundIsReady event...

... until the user clicks the header of dgvFound to sort. After the sort everything goes pear-shaped with a NullReferenceException.

 

Some code:

       ...yada yada yada to prepare cmd

       '// exec the sproc
       conn1.Open()
       Dim oDr As SqlDataReader = cmd.ExecuteReader()

       '// clear any entries in existing datatable dtFound
       dtFound.Rows.Clear()
       dtFound.Columns.Clear()
       dtFound.Clear()

       '// refill dtFound
       Dim i As Integer
       Dim count As Integer = oDr.FieldCount - 1

       '//add columns
       For i = 0 To count
           dtFound.Columns.Add(oDr.GetName(i), oDr.GetFieldType(i))
       Next

       '//add rows
       Do While oDr.Read()
           Dim r As DataRow = dtFound.NewRow
           For i = 0 To count
               r(i) = oDr.Item(i)
           Next [b][color="Red"]
'NullReferenceException on next line if dgvFound has been sorted by user [/color]
           dtFound.Rows.Add(r) [/b]
       Loop

       '// raise an event to let the application know dtFound is filled

and then in the event handler:

       Me.dgvFound.DataSource = dtFound

       '// WORKAROUND to evade NullReferenceException after sort
       Dim i As Integer
       For i = 0 To dgvFound.ColumnCount - 1
           Me.dgvFound.Columns(i).SortMode = DataGridViewColumnSortMode.NotSortable
       Next

 

The users can live without sorting - so for the time being I have simply turned sort off, but I would like to understand what is happening here, and how I might be able to leave sorting on.

 

Chris

[PlausiblyDamp]

Does the NullReference indicate what is null? i.e. is it dtFound, it's Rows or the variable r?

[chris1028]

Test: find 2 columns x 30 rows, sort the datagrid, rerun the same 2 x 30 to throw the exception.

dtFound is alive when the exception is thrown:

 

>? oDr.fieldcount

2

>? count

1

>? i

2

>? dtfound.rows.count

2

>? dtfound.columns.count

2

 

Here is a (partial) stack trace:

System.NullReferenceException was unhandled
 Message="La référence d'objet n'est pas définie à une instance d'un objet."
 Source="System.Data"
 StackTrace:
   à System.Data.Index.CompareRecords(Int32 record1, Int32 record2)
   à System.Data.Index.IndexTree.CompareNode(Int32 record1, Int32 record2)
   à System.Data.RBTree`1.RBInsert(Int32 root_id, Int32 x_id, Int32 mainTreeNodeID, Int32 position, Boolean append)
   à System.Data.RBTree`1.InsertAt(Int32 position, K item, Boolean append)
   à System.Data.Index.InsertRecord(Int32 record, Boolean fireEvent)
   à System.Data.Index.ApplyChangeAction(Int32 record, Int32 action, Int32 changeRecord)
   à System.Data.DataTable.RecordStateChanged(Int32 record1, DataViewRowState oldState1, DataViewRowState newState1, Int32 record2, DataViewRowState oldState2, DataViewRowState newState2)
   à System.Data.DataTable.SetNewRecordWorker(DataRow row, Int32 proposedRecord, DataRowAction action, Boolean isInMerge, Int32 position, Boolean fireEvent, Exception& deferredException)
   à System.Data.DataTable.InsertRow(DataRow row, Int32 proposedID, Int32 pos, Boolean fireEvent)
   à System.Data.DataRowCollection.Add(DataRow row)
   à <myapplication>.ucFinderXxxx.butShowSearch_Click(Object sender, EventArgs e) dans D:\Development\Projects\<myapplication>\ucFinderXxxx.vb:ligne 158

Sorry it is in "Microsoft French".

 

Chris

[chris1028]

mmm - didn't know I could do this:

>? r
{System.Data.DataRow}
   HasErrors: False
   Item: In order to evaluate an indexed property, the property must be qualified and the arguments must be explicitly supplied by the user.
   Item: In order to evaluate an indexed property, the property must be qualified and the arguments must be explicitly supplied by the user.
   Item: In order to evaluate an indexed property, the property must be qualified and the arguments must be explicitly supplied by the user.
   Item: In order to evaluate an indexed property, the property must be qualified and the arguments must be explicitly supplied by the user.
   Item: In order to evaluate an indexed property, the property must be qualified and the arguments must be explicitly supplied by the user.
   ItemArray: {Length=2}
   RowError: ""
   RowState: Added {4}
   Table: {System.Data.DataTable}
>? oDr
{System.Data.SqlClient.SqlDataReader}
   Depth: 0
   FieldCount: 2
   HasRows: True
   IsClosed: False
   Item: In order to evaluate an indexed property, the property must be qualified and the arguments must be explicitly supplied by the user.
   RecordsAffected: -1
   VisibleFieldCount: 2

 

Chris

[chris1028]

and one more:

>? dtFound
{System.Data.DataTable}
   CaseSensitive: False
   ChildRelations: {System.Data.DataRelationCollection.DataTableRelationCollection}
   Columns: {System.Data.DataColumnCollection}
   Constraints: {System.Data.ConstraintCollection}
   Container: Nothing
   DataSet: Nothing
   DefaultView: {System.Data.DataView}
   DesignMode: False
   DisplayExpression: ""
   ExtendedProperties: Count = 0
   HasErrors: False
   IsInitialized: True
   Locale: {System.Globalization.CultureInfo}
   MinimumCapacity: 50
   Namespace: ""
   ParentRelations: {System.Data.DataRelationCollection.DataTableRelationCollection}
   Prefix: ""
   PrimaryKey: {Length=0}
   RemotingFormat: Xml {0}
   Rows: {System.Data.DataRowCollection}
   Site: Nothing
   TableName: ""

 

Chris

[stumper66]

are you using cross-theading?

If the thread that's adding the rows is not the UI thread, I would guess that's the cause.

[chris1028]

Thanks, but no - it's not a threading issue.

It really was related to sorting - and the simple fix was to remove the sort before refilling the datatable:

 

 

 

...yada yada

       '// exec the sproc
       conn1.Open()
       Dim oDr As SqlDataReader = cmd.ExecuteReader()

[color="RoyalBlue"]
       '// remove any dtFound sorting before refilling it
       dtFound.DefaultView.Sort = String.Empty
[/color]

       '// clear any entries in existing datatable dtFound
       dtFound.Rows.Clear()
       dtFound.Columns.Clear()
       dtFound.Clear()

       '// refill dtFound
       Dim i As Integer


yada yada...

 

Chris