Failing to add different items in combobox on dynamic radiobutton click

Question

I am working on radiobuttons and combobox in my wpf App. Although I am a C++ developer, I recently moved to C#. My app deals with dynamic generation of the above mentioned components. Basically I have created 4 dynamic radiobuttons in my app and on clicking each, i should should add different items to my combobox. Here is the code:

XAML:

<ItemsControl ItemsSource="{Binding Children}">
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Vertical" >
                        <RadioButton Content="{Binding RadioBase}"  Margin="0,10,0,0"  IsChecked="{Binding BaseCheck}" GroupName="SlotGroup"  Height="15" Width="80" HorizontalAlignment="Center" VerticalAlignment="Center"/>                            
                    </StackPanel>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ItemsControl>

<ComboBox Visibility="{Binding IsRegisterItemsVisible}" ItemsSource="{Binding RegComboList}" SelectedItem="{Binding SelectedRegComboList, Mode=TwoWay}" SelectedIndex="0" />

FPGARadioWidgetViewModel Class:

public ObservableCollection<FPGAViewModel> Children { get; set; }

    public FPGARadioWidgetViewModel()
    {
        Children = new ObservableCollection<FPGAViewModel>();
        Children.Add(new FPGAViewModel() { RadioBase = "Base 0x0", ID = 0 });
        Children.Add(new FPGAViewModel() { RadioBase = "Base 0x40", ID = 1 });
        Children.Add(new FPGAViewModel() { RadioBase = "Base 0x80", ID = 2 });
        Children.Add(new FPGAViewModel() { RadioBase = "Base 0xc0", ID = 3 });            
    }

FPGAViewModel Class:

private bool sBaseCheck;
    public bool BaseCheck
    {
        get { return this.sBaseCheck; }
        set
        {
            this.sBaseCheck = value;                
            AddComboItems();
            this.OnPropertyChanged("BaseCheck");
        }
    }    

private ObservableCollection<string> _RegComboList;
    public ObservableCollection<string> RegComboList
    {
        get { return _RegComboList; }
        set
        {
            _RegComboList = value;
            OnPropertyChanged("RegComboList");
        }
    }        

private void AddComboItems()
    {
        int baseRegister = 0x40 * ID;
        ObservableCollection<string> combo = new ObservableCollection<string>();            

        for (int i = 0; i < 0x40; i++)
        {
            int reg = (i * 8) + baseRegister;
            combo[i] = "0x" + reg.ToString("X");
        }

        RegComboList = new ObservableCollection<String>(combo);
        OnPropertyChanged("RegComboList");
    }


private bool isRegisterItemsVisible = false;
    public bool IsRegisterItemsVisible
    {
        get { return isRegisterItemsVisible; }
        set
        {
            isRegisterItemsVisible = value;
            OnPropertyChanged("IsRegisterItemsVisible");                
            OnPropertyChanged("RegComboList");
        }
    }

If you notice, on clicking a particular radiobutton, it should add items with different value in combobox based on ID. It has to be made sure that on clicking any radiobutton only the items of that should be added and previous content of combobox should be cleared. I am trying to do the same thing using my above code but nothing seems to appear in combobox when i debug.

Please help :)

Answer 1

I would associate the ItemsSource of your ComboBox with the selected RadioButton. From your existing model I would make every FPGAViewModel have an ObservableCollection<string> which you have done. Then, as Alex Curtis said, you would create a binding between the selected radio button and the combo box's ItemsSource.

Have a look at this post, it is probably easier to get the selected radio button by changing your ItemsControl to use a ListBox with the existing DataTemplate. You can then bind the IsChecked property to the ListBoxItem.IsSelected.

           <ListBox ItemsSource="{Binding Children}" SelectedItem="{Binding YourSelectedItem}">
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <StackPanel Orientation="Vertical" >
                            <RadioButton Content="{Binding RadioBase}"  Margin="0,10,0,0"  GroupName="SlotGroup"  Height="15" Width="80" HorizontalAlignment="Center" VerticalAlignment="Center">
                                <RadioButton.IsChecked>
                                    <Binding Path="IsSelected"
                                     RelativeSource="{RelativeSource AncestorType=ListBoxItem}" Mode="TwoWay" />
                                </RadioButton.IsChecked>
                            </RadioButton>                            
                        </StackPanel>
                    </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>


<ComboBox Visibility="{Binding YourSelectedItem.IsRegisterItemsVisible}" ItemsSource="{Binding YourSelectedItem.RegComboList}" SelectedItem="{Binding YourSelectedItem.SelectedRegComboList, Mode=TwoWay}" SelectedIndex="0" />

Then in the ViewModel that contains the Children collection you need to have a:

    private FPGAViewModel _yourSelectedItem;

    public FPGAViewModel YourSelectedItem
    {
        get { return _yourSelectedItem; }
        set { _yourSelectedItem = value;
        OnPropertyChanged("YourSelectedItem");}
    }

To populate your items I would change the constructor of FPGAViewModel to accept the Base and ID as parameters so you can call AddComboItems() in the constructor.

public FPGAViewModel(string radioBase, int id)
{
    RadioBase = radioBase;
    ID = id;
    AddComboItems();
}

Now

Children.Add(new FPGAViewModel() { RadioBase = "Base 0x0", ID = 0 });

should become

Children.Add(new FPGAViewModel("Base 0x0", 0));

Answer 2

That is because the combobox has been bound to a different reference of strings. Every radio click changes the items and returns a new reference to a list. Try reusing the current RegComboList by removing the existing items within it and then add the new ones. If that fails to update the combobox, make the binding to RegComboList two way.

Edit: Here is a working example .Net 4.5, don't worry the concepts are the same.

Here the combo box is loaded initially with 5 words. Then every time a user clicks the button, a new set of words is put into the list, changing the combo box. Note the clear done for the collection.

The picture is after the initial "Lorem Ipsum" load...

<Window x:Class="WPFCombo.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">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="50*" />
            <RowDefinition Height="50*" />
            <RowDefinition Height="172*" />
        </Grid.RowDefinitions>
        <Button Content="Button"
                HorizontalAlignment="Center"
                VerticalAlignment="Center"
                Width="75"
                Click="Button_Click_1" />
        <ComboBox HorizontalAlignment="Center"
                  Grid.Row="1"
                  ItemsSource="{Binding RegComboList}"
                  VerticalAlignment="Center"
                  Width="120" />
    </Grid>
</Window>

Code behind

public partial class MainWindow : Window,  INotifyPropertyChanged
{
    private const string cLorem = @"Lorem ipsum dolor sit amet consectetur adipiscing elit Maecenas
                                   et lacinia nisl Aenean nec aliquet risus Phasellus dui purus 
                                   sollicitudin nec cursus vitae cursus id purus Nam quis risus 
                                   velit Sed aliquam tellus in odio pulvinar tincidunt Sed bibendum mi";



    private int Skip { get; set; }
    private ObservableCollection<string> _RegComboList;
    public event PropertyChangedEventHandler PropertyChanged;

    public ObservableCollection<string> RegComboList
    {
        get { return _RegComboList; }
        set
        {
            _RegComboList = value;
            OnPropertyChanged();
        }
    }


    public MainWindow()
    {
        InitializeComponent();
        RegComboList = new ObservableCollection<string>();
        GenerateWords(5);

        DataContext = this;
    }

    private void GenerateWords(int toTake)
    {
        RegComboList.Clear();

        Regex.Split(cLorem, @"\s+").Skip(Skip)
             .Take(toTake)
             .ToList()
             .ForEach(word => RegComboList.Add( word ));

        Skip += toTake;

    }

    protected virtual void OnPropertyChanged( [CallerMemberName] string propertyName = "" )
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            handler( this, new PropertyChangedEventArgs( propertyName ) );
        }
    }

    private void Button_Click_1(object sender, RoutedEventArgs e)
    {
        GenerateWords(new Random().Next(1, 10));
    } 
}