WPF ComboBox with CheckBoxes display info about checked items?

Question

Im trying to make a ComboBox that have checkboxes as items and based on what is checked display different things when the combobox is "closed".

The look Im trying achieve can be seen in the image.

Ideally I dont want the user to be able to select the text in the top ( in the image).

Is there a simple solution to this? I've seen solutions where one can display more information when all the items are shown by using DataTriggers to hide different nested controls, but that is not really what Im looking for.

Any ideas?

/Erik

Answer 1

Here is a way to achieve most of what you want using a ComboBox, except that the text can still be selected (using custom text only works when IsEditable is true). It is not editable though because of IsReadOnly="true".

View

<ComboBox
    IsEditable="True"
    IsReadOnly="True"
    ItemsSource="{Binding Items}"
    Text="{Binding Text}">
    <ComboBox.ItemTemplate>
        <DataTemplate
            DataType="{x:Type local:Item}">
            <CheckBox
                Content="{Binding Name}"
                IsChecked="{Binding IsChecked}" />
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>

Viewmodel

// ObservableObject is a custom base class that implements INotifyPropertyChanged
internal class MainWindowVM : ObservableObject
{
    private ObservableCollection<Item> mItems;
    private HashSet<Item> mCheckedItems;

    public IEnumerable<Item> Items { get { return mItems; } }

    public string Text
    {
        get { return _text; }
        set { Set(ref _text, value); }
    }
    private string _text;

    public MainWindowVM()
    {
        mItems = new ObservableCollection<Item>();
        mCheckedItems = new HashSet<Item>();
        mItems.CollectionChanged += Items_CollectionChanged;

        // Adding test data
        for (int i = 0; i < 10; ++i)
        {
            mItems.Add(new Item(string.Format("Item {0}", i.ToString("00"))));
        }
    }

    private void Items_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (e.OldItems != null)
        {
            foreach (Item item in e.OldItems)
            {
                item.PropertyChanged -= Item_PropertyChanged;
                mCheckedItems.Remove(item);
            }
        }
        if (e.NewItems != null)
        {
            foreach (Item item in e.NewItems)
            {
                item.PropertyChanged += Item_PropertyChanged;
                if (item.IsChecked) mCheckedItems.Add(item);
            }
        }
        UpdateText();
    }

    private void Item_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (e.PropertyName == "IsChecked")
        {
            Item item = (Item)sender;
            if (item.IsChecked)
            {
                mCheckedItems.Add(item);
            }
            else
            {
                mCheckedItems.Remove(item);
            }
            UpdateText();
        }
    }

    private void UpdateText()
    {
        switch (mCheckedItems.Count)
        {
            case 0:
                Text = "<none>";
                break;
            case 1:
                Text = mCheckedItems.First().Name;
                break;
            default:
                Text = "<multiple>";
                break;
        }
    }
}

// Test item class
// Test item class
internal class Item : ObservableObject
{
    public string Name { get; private set; }

    public bool IsChecked
    {
        get { return _isChecked; }
        set { Set(ref _isChecked, value); }
    }
    private bool _isChecked;

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

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

If the selectable text is an issue, you may want to create a custom ComboBox control template (default example here). Alternatively, you could use something else instead of a ComboBox, and make it look like a ComboBox.

Screenshot of example: