Binding background value in wpf datagrid cell

Question

I have a WPF app in VS2015. It's been developed as MVVM with nothing in the code-behind classes.

It has a user control containing a datagrid. I would like the background colour of any edited cell to be changed from white to red. I have a button bound to a method in the view model that applies the changed data to a database.

My problem is the binding of the Background property of the datagrid column.

My ViewModel contains:

private ObservableCollection<ComparisonRec> _piToAccessFilteredRecs;

The ComparisonRec implements ClientEntityBase

public class ComparisonRec : ClientEntityBase

This has an IsDirty property

I have the following ValueConverter class:

public class DirtyToBrushConverter : IValueConverter
    {

        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            Brush ret;

            if ((bool)value == true)
            {
                ret = Brushes.Red;
            }
            else
            {
                ret = Brushes.White;
            } 

            return ret;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotSupportedException();
        }
    }

The data context for my user control is set as follows:

    <UserControl.DataContext>
        <local:CompareUCViewModel />
    </UserControl.DataContext>

In the DataGrid I have the binding:

ItemsSource="{Binding PiToAccessFilteredRecs}"

For the DataGridTextColumn that I need to highlight a change, I have the following binding:

Binding="{Binding Path=Access_Notes, Mode=TwoWay, UpdateSourceTrigger=LostFocus}">

This works fine to display the data. To try and get the highlighting, I added the following:

<DataGridTextColumn.ElementStyle>
                                <Style TargetType="{x:Type TextBlock}">
                                    <Setter Property="Background" Value="{Binding Access_Notes.IsDirty, Converter={StaticResource DirtyToBrushConverter}}" />
                                </Style>
                            </DataGridTextColumn.ElementStyle>

It's not working :( I see the following in the output window for each row displayed:

System.Windows.Data Error: 40 : BindingExpression path error: 'IsDirty' property not found on 'object' ''String' (HashCode=577941586)'. BindingExpression:Path=Access_Notes.IsDirty; DataItem='ComparisonRec' (HashCode=27207830); target element is 'TextBlock' (Name=''); target property is 'Background' (type 'Brush')

Can anyone see where I went wrong please?

EDIT As per @XAMIMAX suggestion, if I change binding to:

<Setter Property="Background" Value="{Binding Access_Notes

The the string value of Access_Notes (the content that would be displayed in the grid cell) is passed to the value converter and an exception is thrown because this can't be cast to (bool)

Can you bind the entire Access_Notes and analyse it in your converter and see what you get? — XAMlMAX
– XAMlMAX, Commented May 5, 2017 at 15:28

Community · Accepted Answer · 2017-05-23 12:10:36Z

1

I found the answer here: binding to a property of an object

Because the DataGridTextColumn was already binding to Access_Notes this meant my setter just needed to bind to the IsDirty property as follows:

Value="{Binding IsDirty

For completeness, my working xaml is as follows:

<DataGridTextColumn x:Name="access_NotesColumn" Width="SizeToHeader" Header="Access Notes" Binding="{Binding Path=Access_Notes, Mode=TwoWay, UpdateSourceTrigger=LostFocus}">
                                <DataGridTextColumn.ElementStyle>
                                    <Style TargetType="{x:Type TextBlock}">
                                        <Setter Property="Background" Value="{Binding IsDirty, Converter={StaticResource DirtyToBrushConverter}}" />
                                    </Style>
                                </DataGridTextColumn.ElementStyle>
                            </DataGridTextColumn>

edited May 23, 2017 at 12:10

CommunityBot

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answered May 6, 2017 at 6:37

Rob Bowman

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