C# WPF binding - Combobox selecteditem to Listbox?

Question

I am trying to bind a ComboBox, which have two categories (Letters and Numbers), to a Listbox.

Here is the C# Code:

 class LibraryViewModel
{
    public LetterOrNumberList lib { get; }

    public LibraryViewModel()
    {
        lib = new LetterOrNumberList();
    }
}


public class LetterOrNumberList : ObservableCollection<LettersAndNumbers>
{
    public LetterOrNumberList()
    {
        LettersAndNumbers Letters = new LettersAndNumbers();
        Letters.Title = "Letters";
        ObservableCollection<IExample> letters = new ObservableCollection<IExample>();
        letters.Add(new LetterA());
        letters.Add(new LetterB());
        Letters.LetterOrNumber = letters;

        LettersAndNumbers Numbers = new LettersAndNumbers();
        Numbers.Title = "Numbers";
        ObservableCollection<IExample> numbers = new ObservableCollection<IExample>();
        numbers.Add(new Number1());
        numbers.Add(new Number2());
        Numbers.LetterOrNumber = numbers;

        this.Add(Letters);
        this.Add(Numbers);
    }
}

public class LettersAndNumbers
{
    public string Title { get; set; }
    public ObservableCollection<IExample> LetterOrNumber { get; set; }
}

public class LetterA : PropertyChangeClass, IExample
{
    public string value
    {
        get
        {
            return _value;
        }

        set
        {
            _value = value;
            OnPropertyChanged(nameof(value));
        }
    }

    public LetterA()
    {
        value = "A";
    }

    private string _value;
}
public class LetterB : PropertyChangeClass, IExample
{
   //principial the same like class Letter A
   //...
}
public class Number1 : PropertyChangeClass, IExample
{
    //principial the same like class Letter A
    //...
}
public class Number2 : PropertyChangeClass, IExample
{
    //principial the same like class Letter A
    //...
}
public class PropertyChangeClass
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string PropertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(PropertyName));
    }
}
public interface IExample
{
    string value { get; set; }
}

And in XAML I tried it as following:

<ComboBox Width="100" Name="cBox" Text="Bitte auswählen" ItemsSource="{Binding lib}" DisplayMemberPath="Title"/>
<ListBox Grid.Row="2" ItemsSource="{Binding cBox}" DisplayMemberPath="value"/>

The ComboBox binding works but I dont know how to bind the nested "value" property in dependency of the selecteditem.

ComboBox

Maybe someone know how to solve. Thanks!

EDIT:

I've a library of different products. Each product is to a category assigned. At the end the user should select a category and the products of it will be dynamically displayed (in a ListBox). I ve sorted it in a observablecollection that Ive the same structure like the code above.

Maybe a better question would be what exactly do you need with this binding? What will be the final result? — ΩmegaMan

user23623447 user23623447 · Accepted Answer · 2019-12-08T13:30:29

I finally get it:

<ListBox Grid.Row="2" ItemsSource="{Binding ElementName=cBox, Path=SelectedItem.LetterOrNumber, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">
        <ListBox.ItemTemplate>
            <DataTemplate>
                <Grid>
                    <TextBlock Text="{Binding Path=value}"/>
                </Grid>
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>

C# WPF binding - Combobox selecteditem to Listbox?

1 Answers