Question

When I select (by clicking or by keyboard) blank row on my DataGrid (when I want to add new row), unexpected validation error occurs (but with no exception) – the border of datagrid changes to red color, as you can see on the image below. When I click second time on blank row, the red border dissapears. Everything other works fine, the new row is added. Besides, I don’t have any validation rules. And when I make a row with empty text, value is valid.

I don’t want this behavior and this red border, anybody knows, why this happens and how to fix it? Why and where some validation fails?

Below I append some source code:

DataGrid definition in xaml:

    <DataGrid IsSynchronizedWithCurrentItem="True" DisplayMemberPath="Name" 
 ItemsSource="{Binding Path=ConfigFiles}" SelectedItem="{Binding Path=SelectedConfigFile}" 
              Grid.Column="1" Height="87" Margin="0,26,11,32" Style="{DynamicResource DataGridStyle}">
        <DataGrid.Columns>
            <DataGridTextColumn Width="1*" Binding="{Binding Name}" />
        </DataGrid.Columns>
    </DataGrid>

My ViewModel’s part:

public class ManageModulesVM : BaseVM  // Implements INotifyPropertyChanged
{
    // ...

    public ObservableCollection<ConfigFile> ConfigFiles
    {
        get { return selectedModule == null ? null : selectedModule.ConfigFiles; }
        set
        {
            selectedModule.ConfigFiles = value;
            OnPropertyChanged(() => ConfigFiles);
        }
    }

    public ConfigFile SelectedConfigFile
    {
        get { return selectedModule == null ? null : selectedModule.SelectedConfigFile; }
        set
        {
            if (value != null)
            {
                selectedModule.SelectedConfigFile = value;
            }
            OnPropertyChanged(() => SelectedConfigFile);
            OnPropertyChanged(() => Parameters);
        }
    }

    // ...
}

ConfigFile class:

public class ConfigFile
{
    public string Name { get; set; }
    public IList<Parameter> Parameters { get; set; }

    public ConfigFile() { Name = ""; Parameters = new List<Parameter>(); }
}

Edit:
After further investigation I know, that SelectedItem Binding is causing problems (when I remove this binding, validation error stops to appear), but I still don’t know why and how to fix this.

Answer 1

I’ve found my own solution to this question. I’ve written a value converter and tied it to the binding:

(SelectedItem="{Binding Path=SelectedConfigFile,Converter={StaticResource configFileConverter}}")

The converter class:

namespace Converters
{
    public class SelectedConfigFileConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return value;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if(value is ConfigFile)
                return value;
            return null;
        }
    }
}

Define resource in resources.xaml file (or in any other resources place):

<ResourceDictionary (...) xmlns:conv="clr-namespace:Converters" >
    <conv:SelectedConfigFileConverter x:Key="configFileConverter" />
</ResourceDictionary>

The advantage of this solution is that the SelectedConfigFile property’s type did’t changed (to the general object type) so it is still strongly typed.