ComboBox绑定-接收有关ComboBox项更改的通知

Question

I want to display a list of ComboBoxes , each ComboBox gets its master list from its parent DataContext but its value is bound to list that drives the list of ComboBoxes

Essentially I have a master list of items ( AvailableRegisters ). I then display a list of ComboBoxes which basically equate to the currently selected Register s

What works

• I can see the correct number of ComboBoxes per SelectedRegisters

What doesnt work

• When I select another item from the combobox I do not receive a CollectionChanged event

ViewModel Code: Here is my (shortened) ViewModel code

public class DialogViewModel : ViewModelBase
{
    public ObservableCollection<IOViewModel> InputOutputList { get; set; }
    public ObservableCollection<AvailableRegister> AvailableRegisters { get; set; }
}

public class IOViewModel
{
    public ObservableCollection<AvailableRegister> SelectedRegisters { get; set; }

    public IOViewModel()
    {
        this.Registers = new ObservableCollection<AvailableRegister>();
        this.Registers.CollectionChanged += Registers_CollectionChanged;
    }

    void Registers_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        // Never hit when changing combo box
    }
}

XAML

<ItemsControl Grid.Column="4" ItemsSource="{Binding SelectedRegisters, Mode=TwoWay}" ItemTemplate="{StaticResource ItemTemplate}"></ItemsControl>

<DataTemplate x:Key="ItemTemplate">
    <ComboBox SelectedValue="{Binding Path=DataContext, RelativeSource={RelativeSource Self},Mode=TwoWay}" ItemsSource="{Binding DataContext.AvailableRegisters, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=UserControl}, Mode=TwoWay}">
        <ComboBox.ItemTemplate>
            <DataTemplate><!-- Display it here --></DataTemplate>
        </ComboBox.ItemTemplate>
    </ComboBox>
</DataTemplate>

Answer 1

The problem is you are only selecting an item from the ComboBox from your ObservableCollection. You aren't changing the collection itself.

If you want, create a property on your ViewModel called SelectedItem then bind your SelectedItem to it.

public class IOViewModel
{
    public ObservableCollection<AvailableRegister> SelectedRegisters { get; set; }

    private AvailableRegister _selectedRegister;
    public AvailableRegister SelectedRegister { get { return _selectedRegister; } set { _selectedRegister = value; } }

    public IOViewModel()
    {
        this.Registers = new ObservableCollection<AvailableRegister>();
        this.Registers.CollectionChanged += Registers_CollectionChanged;
    }

    void Registers_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        // Never hit when changing combo box
    }
}

---

<DataTemplate x:Key="ItemTemplate">
    <ComboBox SelectedItem="{Binding DataContext.SelectedItem, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=UserControl}}" ItemsSource="{Binding DataContext.AvailableRegisters, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=UserControl}, Mode=TwoWay}">
        <ComboBox.ItemTemplate>
            <DataTemplate><!-- Display it here --></DataTemplate>
        </ComboBox.ItemTemplate>
    </ComboBox>
</DataTemplate>