WPF Combobox SelectedItem Problem

Question

Hello,

I am failing in achieving a very simple functionality from a WPF ComboBox.

My ComboBox needs to list a collection of values. This works fine. The value id is also saved succesfully in the database. The problem is that when i want to open the window in edit mode, the combo stays empty. Here is the code :

            <ComboBox Height="28" 
                  HorizontalContentAlignment="Center" 
                  Name="cmbActivity"
                  ItemsSource="{Binding Path=Unit.UnitActivities}"
                  SelectedValuePath="Id"
                  SelectedValue="{Binding Path=UnitActivityId}"
                  Style="{StaticResource comboBoxInError}" 
                  Width="200" 
                  Margin="6" 
                  HorizontalAlignment="Left">
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock FlowDirection="LeftToRight" Text="{Binding Path=ActivityTime.Name}" />
                </DataTemplate>
            </ComboBox.ItemTemplate>
            <ComboBox.SelectedItem>
                <Binding ElementName="cmbActivity" Path="UnitActivityId" UpdateSourceTrigger="PropertyChanged">
                    <Binding.ValidationRules>
                        <ExceptionValidationRule />
                        <val:NotEmptyValidationRule />
                        <val:UnitResTimeOverlapValidationRule />
                    </Binding.ValidationRules>
                </Binding>
            </ComboBox.SelectedItem>
        </ComboBox>

I understand my problem is somewhere in the SelectedItem section, but i just could not figure where and why.

Please help..

Thanks,

Answer 1

Try changing

<Binding ElementName="cmbActivity" Path="UnitActivityId" UpdateSourceTrigger="PropertyChanged">

to:

<Binding Path="UnitActivityId" UpdateSourceTrigger="PropertyChanged">

by removing the ElementName. It makes no sense to set the binding source to itself because the data context will infer this by default.

Answer 2

I am posting the answer for the original problem. This is idenctical to : http://stackoverflow.com/questions/3865738/wpf-cloned-detached-object-edit-problem-what-is-the-standard

1. First implement your cloneable object container :

   public class ClonableObjectContainer : Object , ICloneable
   {
       private Object data;
   
   
   public ClonableObjectContainer(Object obj)
   {
       data = obj;
   }
   
   
   public Object Data
   {
       get { return data; }
   }
   
   
   public object Clone()
   {
       return (ClonableObjectContainer)this.MemberwiseClone();
   }
   
   
   }
   

2. Then use this object with its Clone method to create your detached edit object:

            ClonableObjectContainer coc = new ClonableObjectContainer(actor);
            EntityObject editEntity = (EntityObject)coc.Data;
   

3. After performing changes, detach the original object from the ObjectContext , attach the cloned object, change its state to EntityState.Modified and gracefully save:

           ContextManager.CurrentObjectContext.Detach(oldItem);
           ContextManager.CurrentObjectContext.Attach((IEntityWithKey)item);
           ContextManager.CurrentObjectContext.ObjectStateManager.ChangeObjectState(item, EntityState.Modified); 
           ContextManager.Save();
   

Hope it helps... Oran