Changing ItemSource with SelectedValue binding

[Chad]

If I have a class such as:

class Table
{
    public string Name;
    public string GroupBy;
    public ColumnList Columns;
}

I have a listbox bound to a list of Table objects.  When a table is selected, I want to show a combobox that will let the user pick from the list columns and set Table.GroupBy to the SelectedColumn.Name.

<telerik:RadComboBox DisplayMemberPath="DisplayName" SelectedValuePath="Name"
SelectedValue="{Binding SelectedTable.GroupBy, Mode=TwoWay}"
ItemsSource="{Binding SelectedTable.Columns}"></telerik:RadComboBox>

Sets the selected value before the ItemsSource is loaded, so the value is not displayed.


<telerik:RadComboBox DisplayMemberPath="DisplayName" SelectedValuePath="Name"
ItemsSource="{Binding SelectedTable.Columns}"
SelectedValue="{Binding SelectedTable.GroupBy, Mode=TwoWay}" ></telerik:RadComboBox>

When SelectedTable is changed, the ItemsSource is cleared out first and GroupBy is set to null.


What is the correct way to handle this scenario?

[George]

Hello Chad,

Could you please give us some details about ColumnList type? If you send us a sample project that reproduces your scenario, it would be very helpful.

I am glad to assist you further. 

Best wishes,
George
the Telerik team

[Chad]

ColumnList is an observable collection of Columns:

class Column
{
    public string DisplayName;
    public string Name;
}

All of my properties implement INotifyPropertyChanged.  The silverlight combobox has the same bug:  https://connect.microsoft.com/VisualStudio/feedback/details/523394/silverlight-forum-combobox-selecteditem-binding

The workaround that works for me is:

public class ComboBox : System.Windows.Controls.ComboBox
{ 
    protected override void OnItemsChanged(System.Collections.Specialized.NotifyCollectionChangedEventArgs e) 
    { 
        var bindingExpression = GetBindingExpression(SelectedValueProperty); 
        base.OnItemsChanged(e); 
        if (bindingExpression != null) 
        { 
            var binding = bindingExpression.ParentBinding; 
            SetBinding(SelectedValueProperty, bindingExpression.ParentBinding); 
        } 
    }
}

This workaround doesn't work if I inherit from telerik's RadComboBox.

[George]

Hello Chad,

Could you please send us a sample project that reproduces this problem? This will definitely helps us in further pinpointing the problem. 

Best wishes,
George
the Telerik team

[Chad]

MainPage.zaml:

<UserControl x:Class="ShowColumnsOutsideTheGrid.MainPage"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation"
             xmlns:my="clr-namespace:ShowColumnsOutsideTheGrid"
             mc:Ignorable="d" d:DesignHeight="700" d:DesignWidth="700">
    <UserControl.Resources>
        <my:MyViewModel x:Key="MyViewModel"/>
    </UserControl.Resources>
    <Grid DataContext="{StaticResource MyViewModel}">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>

        <ListBox ItemsSource="{Binding Tables}" DisplayMemberPath="Name"
                 Grid.Column="0" x:Name="tableList"></ListBox>

        <Grid DataContext="{Binding SelectedItem,ElementName=tableList}"
              Grid.Column="1">
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"></RowDefinition>
                <RowDefinition Height="Auto"></RowDefinition>
                <RowDefinition Height="Auto"></RowDefinition>
            </Grid.RowDefinitions>

            <StackPanel Orientation="Horizontal" Grid.Row="0">
                <TextBlock Text="Table Name:" VerticalAlignment="Center"></TextBlock>
                <TextBox Text="{Binding Name, Mode=TwoWay}"></TextBox>
            </StackPanel>

            <StackPanel Orientation="Horizontal" Grid.Row="1">
                <TextBlock Text="Group table by column:" VerticalAlignment="Center"></TextBlock>
                <telerik:RadComboBox ItemsSource="{Binding Columns}" DisplayMemberPath="DisplayName" SelectedValuePath="Name"
                                     SelectedValue="{Binding GroupBy, Mode=TwoWay}"></telerik:RadComboBox>
            </StackPanel>
        </Grid>
    </Grid>
</UserControl>

MyViewModel.cs:

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.ComponentModel;
using System.Collections.ObjectModel;

namespace ShowColumnsOutsideTheGrid
{
    public class Table: PropertyChangedBase
    {
        private string vName;
        public string Name
        {
            get { return vName; }
            set
            {
                vName = value;
                OnPropertyChanged("Name");
            }
        }


        private string vGroupBy;
        public string GroupBy
        {
            get { return vGroupBy; }
            set
            {
                vGroupBy = value;
                OnPropertyChanged("GroupBy");
            }
        }


        private ObservableCollection<Column> vColumns;
        public ObservableCollection<Column> Columns
        {
            get { return vColumns; }
            set
            {
                vColumns = value;
                OnPropertyChanged("Columns");
            }
        }
    }

    public class Column: PropertyChangedBase
    {
        private string vDisplayName;
        public string DisplayName
        {
            get { return vDisplayName; }
            set
            {
                vDisplayName = value;
                OnPropertyChanged("DisplayName");
            }
        }

        private string vName;
        public string Name
        {
            get { return vName; }
            set
            {
                vName = value;
                OnPropertyChanged("Name");
            }
        }
    }


    public class PropertyChangedBase : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged(PropertyChangedEventArgs args)
        {
            PropertyChangedEventHandler handler = this.PropertyChanged;
            if (handler != null)
            {
                handler(this, args);
            }
        }

        protected void OnPropertyChanged(string propertyName)
        {
            this.OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
        }
    }

    public class MyViewModel : PropertyChangedBase
    {
        private ObservableCollection<Table> vTables { get; set; }
        public ObservableCollection<Table> Tables
        {
            get { return vTables; }
            set
            {
                vTables = value;
                OnPropertyChanged("Tables");
            }
        }

        public MyViewModel()
        {
            LoadData();
        }

        private void LoadData()
        {
            Tables = new ObservableCollection<Table>();
            for (int t = 0; t < 10; t++)
            {
                Table table = new Table();
                table.Name = "Table " + t.ToString();
                table.Columns = new ObservableCollection<Column>();

                for (int c = 0; c < 5; c++)
                {
                    Column column = new Column();
                    column.DisplayName = "Field " + c.ToString();
                    column.Name = "table " + t.ToString() + ", Column " + c.ToString();
                    table.Columns.Add(column);
                }

                // pick column 3 for the group by
                table.GroupBy = table.Columns[3].Name;

                Tables.Add(table);
            }
        }
    }
}

It's quick and dirty code, but it shows the bug.  Pick table 1 in the listbox on the left and notice how Field 3 is selected in the combobox.  Now, select table 2 in the listbox and Field 3 will be selected in the combobox.  Select, table 1 in the listbox again and notice that nothing is selected in the combobox!

[George]

Hi Chad,

 
Thank you sending us the code. We are aware of this issue with RadComboBox. Unfortunately, there is no workaround at this stage. We will fix this issue in our future releases.

Best wishes,
George
the Telerik team

[Christophe]

Hi,

We have the same problem. When will you fix this issue ?

BR
Christophe

[Valeri Hristov]

Hello Christophe,

I cannot commit to a specific date for this feature, but we will do our best to provide a solution for this problem by the Q2 2011 release, which is expected in the summer.

Regards,
Valeri Hristov
the Telerik team