CODEWITHSUNDEEP
c#wpfmvvmcomboboxobservablecollection
iop
iop

Reputation: 312

C# WPF ComboBox - Allow item to be selected only once per list

I use C#, WPF and try to use MVVM. So I have an ObservableCollection of MyObjects. The list is rendered into a DataGrid, and one property of MyObject is a static list of items which is shown in a ComboBoxes in each row.

Now I would like to select an item in one row in this combobox, and if it was selected in another row before, the last selection has to be removed to the default value. How can I manage this? My MyObjectViewModel knows about the change of its 'own" combobox but how can it tell the MainViewModel (which holds the ObservableCollection of MyObjects) to change the last selected ComboBox item from another MyObject object?

Upvotes: 3

Views: 1809

Answers (1)

Barracoder
Barracoder

Reputation: 3764

The best way to do this is to change your binding focus to ListCollectionViews as this will allow you to manage the cursor. An example is below:

ViewModel

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Data;

    namespace BindingSample
    {
        public class ViewModel
        {
            private string[] _items = new[] { "Item 1", "Item 2", "Item 3", "Item 4", "Item 5" };

            public ViewModel()
            {
                List1 = new ListCollectionView(_items);
                List2 = new ListCollectionView(_items);
                List3 = new ListCollectionView(_items);

                List1.CurrentChanged += (sender, args) => SyncSelections(List1);
                List2.CurrentChanged += (sender, args) => SyncSelections(List2);
                List3.CurrentChanged += (sender, args) => SyncSelections(List3);
            }

            public ListCollectionView List1 { get; set; }

            public ListCollectionView List2 { get; set; }

            public ListCollectionView List3 { get; set; }

            private void SyncSelections(ListCollectionView activeSelection)
            {
                foreach (ListCollectionView view in new[] { List1, List2, List3 })
                {
                    if (view != activeSelection && view.CurrentItem == activeSelection.CurrentItem)
                        view.MoveCurrentTo(null);
                }
            }
        }
    }

View

<Window x:Class="ContextMenuSample.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <StackPanel Orientation="Vertical">
        <ListBox ItemsSource="{Binding List1}" />
        <ListBox ItemsSource="{Binding List2}" />
        <ListBox ItemsSource="{Binding List3}" />        
    </StackPanel>
</Window>

This will allow you to only have one item selected. It's hard-coded for now but can be easily made more flexible for additional lists.

Upvotes: 1

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