How do you add a generic item to a ComboBox bound to a collection in WPF

Question

I have a ComboBox in a WPF application that is bound to an ObservableCollection of Department objects in a C# ViewModel class. I want to use the combo box to filter another collection by department (And indeed it works for that now) The problem is that I want to add an additional option "All" to the top of the list. Is there a correct way to do this. Making a fake department feels wrong in so many ways.

The ComboBox

<ComboBox ItemsSource="{Binding Path=Departments}" 
          SelectedValue="{Binding Path=DepartmentToShow , Mode=TwoWay}" />

Simon Fox · Accepted Answer · 2010-01-28T20:06:39.563

23

You could use a CompositeCollection as the ItemsSource for the ComboBox to include the "All" option. You need to set the Collection property of the CollectionContainer to your "ObservableCollection of Department objects".

<ComboBox >
    <ComboBox.ItemsSource>
        <CompositeCollection>
            <ComboBoxItem>All</ComboBoxItem>
            <CollectionContainer x:Name="departmentCollection"/>
        </CompositeCollection>
    </ComboBox.ItemsSource>
</ComboBox>

Not sure if this will be suitable for your filtering situation however...

edited Jan 28 '10 at 20:06

answered Jan 28 '10 at 03:32

Simon Fox

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+1 Wow as an experienced WPF programmer I was not even aware of `CompositeCollection`! There are all sorts of workarounds for this when searching the internet, but none mention this! Incredible... – Aviad P. Jan 28 '10 at 07:11
Yeah when i read this i was amazed. I have been doing some looking into it this morning and i think it will do the trick. Right now the filtering is done in the building of the Linq query so I am thinking I can test for 'All' and if that is not selected iterate the peopleCollection. In the future I was planning on refactoring and using a CollectionViewSource to filter the view without requerying; I'm not sure how that would work but for this question I have my answer. Thank You! – Mike B Jan 28 '10 at 16:01
1

@Aviad yes it is a nice solution, one thing that does suck a bit is that you can't bind to the Collection property via DataContext as CompositeCollection is not Freezable. This can be worked around by binding to a static resource... – Simon Fox Jan 28 '10 at 19:59
2

the solution to this question has a an example of how to bind in this manner http://stackoverflow.com/questions/1189052/why-is-compositecollection-not-freezable not particularly pretty IMO but does the trick... – Simon Fox Jan 28 '10 at 20:07
Adding a ComboBoxitem in this manner throws HorizontalContentAlignment and VerticalContentAlignment binding errors. Does anyone have a solution for this? – Julien Oct 21 '13 at 16:06

score 0 · Answer 2 · edited Apr 12 '13 at 14:29

Suppose you have a ComboBox named MyCombo, an entity named MyEntity associated with a DomaineService named MyDomainService.

Do not forget

using System.ServiceModel.DomainServices.Client;

and of course the using working well with your Web site of your entity and DomainService

You call a Proc named :

void LoadEntities()
{
    MyDomainService_Context = new MyDomainService();
    EntityQuery<MyEntity > mQuery = null;

    mQuery = from q in _Context.GetMyDomainServiceQuery()
             select q;

    LoadOperation<MyEntity > loadOpLoadEntities = _Context.Load(mQuery, LoadOpLoadEntitiesCallBack, null);
}

Then in the CallBack function:

void LoadOpLoadEntitiesCallBack(LoadOperation<MyEntity> loadOperation)
{
    if (loadOperation.Entities.Count() > 0)
    {
        List<MyEntity> mList = new List<MyEntity>();
        MyEntity mE = new MyEntity();
        mE.Column1 = -1;
        mE.Column2 = "Default value";
        mList.Add(mE);

        for (int i = 0; i < loadOperation.Entities.Count(); i++)
        {
            mList.Add(loadOperation.Entities.ToList()[i]);
        }

        this.MyCombo.ItemsSource = mList.ToList();
    }
}

This is a MVVM WPF app using Linq to SQL. The Composite COllection solution has been working quite well for a couple years but thanks for the additional input. — Mike B, Apr 12 '13 at 16:43

How do you add a generic item to a ComboBox bound to a collection in WPF

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