C# – dynamic datatemplate with valueconverter

cdatatemplatevalueconverterwpfxaml

I want to show data in a wpftoolkit datagrid where the data is a collection of

public class Thing
{
    public string Foo { get; set; }
    public string Bar { get; set; }
    public List<Candidate> Candidates { get; set; }
}

public class Candidate
{

    public string Name { get; set; }
    public CandidateType CandidateType { get; set; }
}

public enum CandidateType
{
    Type1,
    Type2,
    Type42
}

where the number of candidates in Candidates list is configurable at runtime.

Desired grid layout looks like this

Foo | Bar | Candidate 1 | Candidate 2 | ... | Candidate N

Thus it seems I cannot create a DataTemplate for the candidates in xaml as the binding expression will change.

I add necessary columns in AutoGeneratedColumns event like so:

private void DataGrid_AutoGeneratedColumns(object sender, EventArgs e)
{
    ViewModel vm = DataContext as ViewModel;

    for (int i = 0; i < vm.LotsOfThings.First().Candidates.Count; i++)
    {
        string assName = Assembly.GetExecutingAssembly().GetName().Name;
        ParserContext ctx = new ParserContext();
        ctx.XamlTypeMapper = new XamlTypeMapper(new string[] { assName });
        ctx.XamlTypeMapper.AddMappingProcessingInstruction("src", "WpfToolkitDataGridTester", assName);
        ctx.XmlnsDictionary.Add("", "http://schemas.microsoft.com/winfx/2006/xaml/presentation");
        ctx.XmlnsDictionary.Add("x", "http://schemas.microsoft.com/winfx/2006/xaml");
        ctx.XmlnsDictionary.Add("src", "clr-namespace:WpfToolkitDataGridTester;assembly=" + assName);
        var template = XamlReader.Parse(@"<DataTemplate>
                                            <DataTemplate.Resources>
                                                <src:FooConverter x:Key='fooConverter' />
                                            </DataTemplate.Resources>
                                            <TextBlock  
                                                Foreground='{Binding Candidates[" + i + @"].CandidateType,Converter={StaticResource fooConverter}}'
                                                Text='{Binding Candidates[" + i + @"].Name}' />
                                        </DataTemplate>", ctx) as DataTemplate;
        dg.Columns.Add(new DataGridTemplateColumn
        {
            Header = "Candidate " + (i + 1),
            CellTemplate = template
        });
    }
}

This however fails with the following exception:
The tag 'FooConverter' does not exist in XML namespace 'clr-namespace:WpfToolkitDataGridTester;assembly=WpfToolkitDataGridTester'. Line '3' Position '54'.

Changing the StaticResource to DynamicResource makes no change.

What am I missing?

FWIW: a hardcoded datatemplate

<DataTemplate x:Key="candidateTemplate">
  <DataTemplate.Resources>
    <src:FooConverter x:Key="fooConverter" />
  </DataTemplate.Resources>
  <TextBlock 
    Foreground="{Binding Candidates[0].CandidateType,Converter={StaticResource fooConverter}}"
    Text="{Binding Candidates[0].Name}" />
</DataTemplate>

and the template column defined like so

<wpftk:DataGridTemplateColumn CellTemplate="{StaticResource candidateTemplate}" />

'works' but obviously does not produce the desired result as Candidates[0] is hardcoded.

Best Answer

For whatever reason, it works as expected if I do like this...

    string assName = Assembly.GetExecutingAssembly().GetName().Name;
    StringBuilder sb = new StringBuilder();
    sb.Append("<DataTemplate ");
    sb.Append("xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation' ");
    sb.Append("xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml' ");
    sb.Append("xmlns:src='clr-namespace:WpfToolkitDataGridTester;assembly=" + assName + "' >");
    sb.Append("<DataTemplate.Resources>");
    sb.Append("<src:FooConverter x:Key='fooConverter' />");
    sb.Append("</DataTemplate.Resources>");
    sb.Append("<TextBlock ");
    sb.Append("Foreground='{Binding Candidates[" + i + "].CandidateType,Converter={StaticResource fooConverter}}' ");
    sb.Append("Text='{Binding Candidates[" + i + @"].Name}' />");
    sb.Append("</DataTemplate>");
    var template = (DataTemplate)XamlReader.Parse(sb.ToString());

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You set the DisplayMemberPath and the SelectedValuePath to "Name", so I assume that you have a class PhoneBookEntry with a public property Name.

Have you set the DataContext to your ConnectionViewModel object?

I copied you code and made some minor modifications, and it seems to work fine. I can set the viewmodels PhoneBookEnty property and the selected item in the combobox changes, and I can change the selected item in the combobox and the view models PhoneBookEntry property is set correctly.

Here is my XAML content:

<Window x:Class="WpfApplication6.Window1"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window1" Height="300" Width="300">
<Grid>
    <StackPanel>
        <Button Click="Button_Click">asdf</Button>
        <ComboBox ItemsSource="{Binding Path=PhonebookEntries}"
                  DisplayMemberPath="Name"
                  SelectedValuePath="Name"
                  SelectedValue="{Binding Path=PhonebookEntry}" />
    </StackPanel>
</Grid>
</Window>

And here is my code-behind:

namespace WpfApplication6
{

    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
            ConnectionViewModel vm = new ConnectionViewModel();
            DataContext = vm;
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            ((ConnectionViewModel)DataContext).PhonebookEntry = "test";
        }
    }

    public class PhoneBookEntry
    {
        public string Name { get; set; }

        public PhoneBookEntry(string name)
        {
            Name = name;
        }

        public override string ToString()
        {
            return Name;
        }
    }

    public class ConnectionViewModel : INotifyPropertyChanged
    {
        public ConnectionViewModel()
        {
            IList<PhoneBookEntry> list = new List<PhoneBookEntry>();
            list.Add(new PhoneBookEntry("test"));
            list.Add(new PhoneBookEntry("test2"));
            _phonebookEntries = new CollectionView(list);
        }

        private readonly CollectionView _phonebookEntries;
        private string _phonebookEntry;

        public CollectionView PhonebookEntries
        {
            get { return _phonebookEntries; }
        }

        public string PhonebookEntry
        {
            get { return _phonebookEntry; }
            set
            {
                if (_phonebookEntry == value) return;
                _phonebookEntry = value;
                OnPropertyChanged("PhonebookEntry");
            }
        }

        private void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
        public event PropertyChangedEventHandler PropertyChanged;
    }
}

Edit: Geoffs second example does not seem to work, which seems a bit odd to me. If I change the PhonebookEntries property on the ConnectionViewModel to be of type ReadOnlyCollection, the TwoWay binding of the SelectedValue property on the combobox works fine.

Maybe there is an issue with the CollectionView? I noticed a warning in the output console:

System.Windows.Data Warning: 50 : Using CollectionView directly is not fully supported. The basic features work, although with some inefficiencies, but advanced features may encounter known bugs. Consider using a derived class to avoid these problems.

Edit2 (.NET 4.5): The content of the DropDownList can be based on ToString() and not of DisplayMemberPath, while DisplayMemberPath specifies the member for the selected and displayed item only.

Best Answer

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