Scrolling with virtualization

[Gerard Kerbourch]

Hello!

We have an application, and a part of this allows us to display parts of our DataBase (it can be a great one) in a RadGridView which has Virtualization turned on (we need it).
We applied a style on the dates displayed ("01/01/1900", default date, must be in LightGray color), and when we scroll in a vertical way, the style is not apply like it should (some dates are in LightGray, even if they're not default date, vice versa).
And here is the mysterious one: when we move the horizontal ScrollBar, this problem not happen, and the style is perfectly apply. It's even repairing the problem of the vertical scrolling.

Is there a solution for our first problem?

And isn't the second point a bug?

Thank you!

[Pavel Pavlov]

Hello Gerard Kerbourch,

May I see how do you apply the style. In order to avoid such thing happening the routine approach here would be to apply the style in the RowLoaded event via Binding.

When virtualization is turned on , cells are being reused/recycled which may be the reason for the observed strange behavior. The approach described above should solve the issue.
In case you have furhter troubles, just paste me your code and I will try to find a solution for you.

Best wishes,
Pavel Pavlov
the Telerik team

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[Gerard Kerbourch]

Thank you for the answer!

The problem is partly solved, because now, it's applying the style when we scroll with the horizontal bar. But if we use the vertical one, then the horizontal, it's applying the style on every columns, even if they're not concerned by the style...

When the Virtualization is disabled, the problem disappear but the scrolling is really tedious...

I'd like to send you our code, but our application is really big, and build in a very dynamic way so I'll prefer find a solution without having to send the code, because it will be necessarily a really big part of code...If you see what I mean...

[Gerard Kerbourch]

This is when we use RowLoaded and StyleSelector. When we just use RowLoaded, we have to scroll vertically to see the style applying.

[Pavel Pavlov]

Hi Gerard Kerbourch,

Speaking of style selectors- I have prepared a small app with conditional formatting with style selector.
Please find it attached . I have tested it and it seems to behave correctly .
It does not utilize the RowLoaded events , which simplifies things.

Can you use this approach in your application.

Best wishes,
Pavel Pavlov
the Telerik team

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[Gerard Kerbourch]

Thank you for answering,

We already use this approach, but the problem seems to be with the
But when we use StyleSelector, the horizontal scrolling works well, but when we use the vertical one, on the columns that contains dates, the style is applying in a wrong way, and it's reflected on the others columns.

Here is, finally, the interesting parts of our code:

<UserControl xmlns:controls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls"  x:Class="_3GRC.Silverlight.Controls.Common._3GGrille"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:telerik="clr-namespace:Telerik.Windows.Controls;assembly=Telerik.Windows.Controls.GridView"
    xmlns:telerikGridView="clr-namespace:Telerik.Windows.Controls.GridView;assembly=Telerik.Windows.Controls.GridView"
    Width="Auto" Height="Auto" VerticalAlignment="Stretch" HorizontalAlignment="Stretch"
             xmlns:local="clr-namespace:_3GRC.Silverlight.Controls.Common"
    >

    <UserControl.Resources>
        <DataTemplate x:Key="RuntimeContentTemplate">
            <ContentControl Loaded="ContentControl_Loaded"/>
        </DataTemplate>
    </UserControl.Resources>

    <Grid x:Name="LayoutRoot" Background="White" >
        <Grid.Resources>
            <local:MyStyleSelector x:Key="styleSelector" />
        </Grid.Resources>

        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="24" />
        </Grid.RowDefinitions>

        <telerik:RadGridView Name="grd_Main" Grid.Row="0"
            VerticalAlignment="Stretch" HorizontalAlignment="Stretch"
            ItemsSource="{Binding}" AutoGenerateColumns="False"
            ScrollViewer.HorizontalScrollBarVisibility="Visible" ScrollViewer.VerticalScrollBarVisibility="Visible" ScrollMode="RealTime"
            CellValidating="grd_Main_CellValidating" >
        </telerik:RadGridView>


        <telerik:RadDataPager x:Name="radDataPager" Grid.Row="1"
            PageIndexChanged="radDataPager_PageIndexChanged"
            PageSize="1" Source="{Binding}" DisplayMode="First, Last, Next, Previous, Text"
            IsTotalItemCountFixed="True">

        </telerik:RadDataPager>
    </Grid>

</UserControl>

Our StyleSelector:

Imports Telerik.Windows.Controls
Imports Telerik.Windows.Controls.GridView
Imports System.Windows.Markup


''' <summary>
'''
''' </summary>
''' <remarks></remarks>
Public Class MyStyleSelector
    Inherits StyleSelector

    Public Overloads Overrides Function SelectStyle(ByVal item As Object, ByVal container As DependencyObject) As Style

        Dim Style = New Style(GetType(GridViewCell))

        Dim myCell = DirectCast(container, GridViewCell)

        Style.TargetType = GetType(GridViewCell)

        If myCell.Value.Equals("01/01/1900") Then
            Style.Setters.Add(New Setter(GridViewCell.ForegroundProperty, New SolidColorBrush(Colors.LightGray)))
        Else
            Style.Setters.Add(New Setter(GridViewCell.ForegroundProperty, New SolidColorBrush(Colors.Black)))
        End If

        Return (Style)
    End Function
    Private Shared Function InlineAssignHelper(Of T)(ByRef target As T, ByVal value As T) As T
        target = value
        Return (value)
    End Function
End Class

 
And here, the way we are filling the RadGridView grd_Main

    Public Sub SetDataSource(ByVal data As String)

        Try

            table = New DataTable

            Dim cultureInfo As New CultureInfo("fr-FR")

            For Each item In lst_columns

                Dim ocol As DataColumn = New DataColumn

                With ocol

                    .ColumnName = item.Value.Tag

                    Select Case item.Value.Type
                        Case Is = "adDBTimeStamp"
                            .DataType = System.Type.GetType("System.DateTime")
                            If item.Value.Format.Equals("") Then
                                '.DataType = System.Type.GetType("System.DateTime")
                                DirectCast(grd_Main.Columns(item.Value.Tag), GridViewDataColumn).DataFormatString = "{0:dd/MM/yyyy}"
                            Else
                                DirectCast(grd_Main.Columns(item.Value.Tag), GridViewDataColumn).DataFormatString = "{0:" + item.Value.Format + "}"
                            End If
                            grd_Main.Columns(item.Value.Tag).CellStyleSelector = Me.LayoutRoot.Resources("styleSelector")

                        Case Is = "adBoolean"
                            .DataType = System.Type.GetType("System.Boolean")

                        Case Else
                            .DataType = System.Type.GetType("System.String")

                    End Select

                End With

                table.Columns.Add(ocol)

            Next

            Dim doc = XDocument.Parse(data)
            Dim lng_cptRows As Long = 0

            ' on parse le document XML
            For Each root As XElement In doc.Descendants("Table").Descendants("Table")

                Dim row = New DataRow
                For Each elem As XElement In root.Descendants
                    For Each item In lst_columns
                        If item.Value.Tag.Equals(elem.Name.ToString.Replace(".", "_").Replace(" ", "_")) Then
                            Select Case item.Value.Type

                                Case "adDBTimeStamp"
                                    If elem.Value IsNot Nothing Then
                                        Dim str_DateTemp As String = ""
                                        Dim dt As DateTime = New DateTime()
                                        'DateTime.TryParse(elem.Value.ToString(cultureInfo), cultureInfo, DateTimeStyles.None, dt).ToString()
                                        dt = DateTime.ParseExact(elem.Value.ToString, "MM/dd/yyyy", cultureInfo)
                                        row(item.Value.Tag) = dt
                                    End If
                                Case "adBoolean"
                                    row(item.Value.Tag) = Boolean.Parse(elem.Value)

                                Case Else
                                    row(item.Value.Tag) = elem.Value.ToString

                            End Select
                            Exit For
                        End If
                    Next
                Next
                table.Rows.Add(row)
                Dim str_test As String = ""
                Dim color As Color = New Color
                ' Pour chaque colonne de la datatable
                For Each col In table.Columns
                    ' Si la lng_cptRows-ième colonne de la datatable ne contient pas la colonne courante,
                    If Not table.Rows(lng_cptRows).Keys.Contains(col.ColumnName) Then
                        ' Si cette colonne est de type DateTime
                        If col.DataType Is GetType(DateTime) Then
                            ' On met la valeur "01/01/1900" qui est la date par défaut
                            table.Rows(lng_cptRows).Item(col.ColumnName) = DateTime.Parse("01/01/1900")
                        End If
                    End If
                Next
                lng_cptRows = lng_cptRows + 1
            Next

            grd_Main.ItemsSource = table.ToList()

            ' On passe à False l'a virtualisation de la grille (rafraîchissement des données à chaque scrolling vertical)
            'grd_Main.EnableColumnVirtualization = False

        Catch ex As Exception
            Dim err As ChildErrorBox = New ChildErrorBox(2, New Diagnostics.StackFrame(), , ex.Message)
            err.Show()
        End Try
    End Sub

[Pavel Pavlov]

Hi Gerard Kerbourch,

Both our online samples and the project attached have no problems with vertical scrolling . therefore I am unable to reproduce the issue and provide further assistance .

Can you please open a support ticket and attach your project so we can step trough it  and find what is causing the problem

Regards,
Pavel Pavlov
the Telerik team

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