[Solved] Setting properties of cell content

[Ubaldo]

Hi there, I'm just starting with first rehearsing with your controls and WPF, and I would like to change the color (or any other property) of the text displayed in a bound data column, using a simple ValueConverter that return a Black/Red SolidColorBrush based on the passed value:

MyPublic Function Convert(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object, _
                        ByVal culture As Globalization.CultureInfo) As Object _
                      Implements IValueConverter.Convert
  Dim myColor As New SolidColorBrush(System.Windows.Media.Colors.Black)
  Try
    Dim cur As Decimal = CDec(value)
    If cur < 0 Then myColor = New SolidColorBrush(System.Windows.Media.Colors.Red)
  Catch ex As Exception
  End Try
  Return myColor
End Function

and then in the XAML use an expression like this:

xxxx.ForecolorPropertyName={Binding Path=DataColumnName, Converter=MyClassConverter}

Is this possible ? Or what other way to keep it at simplest ?
regards
Ubaldo

[Maya]

Hello Ubaldo,

The easiest way would be to create a Style targeting the GridViewCell:

<Window.Resources>
    <Style TargetType="telerik:GridViewCell">
        <Setter Property="Foreground" Value="HotPink"/>
    </Style>
</Window.Resources>

In this case the style will be applied to all the cells in the grid. However, you may define the Style explicitly:

<Window.Resources>

    <Style x:Key="MyCellStyle" TargetType="telerik:GridViewCell">

        <Setter Property="Foreground" Value="HotPink"/>

    </Style>   

</Window.Resources>

 

 

<telerik:GridViewDataColumn DataMemberBinding="{Binding Name}"
           CellStyle="{StaticResource MyCellStyle}"/>

You may take a look at our online documentation for further reference. 

Greetings,
Maya
the Telerik team

[Ubaldo]

Hi Maya, thanks for your quick reply.
Probably I don't get very well the concept, due to my inexperience, but what I'm trying to do is to have the fore color of the text that changes in relation to the value of the text. Is less than zero, the color should be Red, otherwise Black.
I know that the quickest way to achieve this in wpf is to create a ValueConverter class that return the color, so that in the binding expression of the value you can add the Converter= parameter that takes is value from the custom converter class.

You suggest to use Styles... so do u mean that I should use a style with a trigger inside ? Well, for sure less straightforward than the Converter used directly in a binding expression.

I would really appreciate a complete sample (easy goal: render the text of a cell in Red if the value of that text is less than zero, otherwise standard Black)

TIA
Ubaldo

[Maya]

Hi Ubaldo,

In this case you may use a CellStyleSelector as described in our online documentation and illustrated in our demos.
 

Regards,
Maya
the Telerik team

[Ubaldo]

Ok, got it. It works, but with some issues that I would like to clarify. First, here the code (my GridView is bound to a CollectionViewSource generated by a standard ADO DataSet, and so returns a DataTable)  

Public Class NumberColorStyle
  Inherits StyleSelector

  Public Property PositiveStyle() As Style
  Public Property NegativeStyle() As Style
  Public Property ColumnName() As String

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

    If TypeOf item Is System.Data.DataRowView Then
      Dim drow As System.Data.DataRowView = CType(item, System.Data.DataRowView)
      If _ColumnName <> "" Then
        Try
          Dim cval As Decimal = CDec(drow.Item(_ColumnName))
          If cval < 0 Then
            Return NegativeStyle
          Else
            Return PositiveStyle
          End If
        Catch ex As Exception
        End Try
      End If
    End If
    Return Nothing

  End Function

End Class

I've tried to make the StyleSelector the more generic as possible, accepting a ColumnName parameter in order to select the column of which to test the value.
In the resources I've defined the two style colors, and the StyleSelector:

<Style x:Key="ForeColorBlackStyle" TargetType="telerik:GridViewCell">
  <Setter Property="Foreground" Value="Black"></Setter>
</Style>
<Style x:Key="ForeColorRedStyle" TargetType="telerik:GridViewCell">
  <Setter Property="Foreground" Value="Red"></Setter>
</Style>
<local:NumberColorStyle x:Key="NumberColorStyle" ColumnName="importo"
                        PositiveStyle="{StaticResource ForeColorBlackStyle}"
                        NegativeStyle="{StaticResource ForeColorRedStyle}"></local:NumberColorStyle>

Now, in the GridWiev xaml, I've referenced the StyleSelector:

<telerik:GridViewDataColumn Header="Importo (EUR)" DataMemberBinding="{Binding importo}"
                            UniqueName="importo" DataFormatString="{} {0:C}"
                            TextAlignment="Right"
                            CellStyleSelector="{StaticResource NumberColorStyle}">

Q1: a lot of xaml for a simple task as this
Q2: if I want to apply this style selector to 20 different columns, should I define 20 different NumberColorStyle static resources so that each one of them can set the ColumnName ? How can I pass the ColumnName directly from the GridViewDataColumn tag ?
TIA
Ubaldo

[Maya]

Hello Ubaldo,

Generally, when you have a lot of items and columns defined, using a IValueConverter is not an optimized solution as it may lead to some performance issues. As for taking the right column in the StyleSelector class, you may use the container argument which will be of type GridViewCell and find the column it belongs to by its Column property:

var cell = container as GridViewCell;
var myColumn = cell.Column as GridViewDataColumn;

Once you get the myColumn variable, you may get its UniqueName property.

Regards,
Maya
the Telerik team