In WPF, I want to dynamically set the itemsource based on combo box selection

Question

I have a Slider and a Combobox in my view. I have 2 properties in my ViewModel. Based on the selection of the combobox, I want to bind any one of the property to the value of the slider.

 private int _xValue;

    public int XValue
    {
        get { return _xValue; }
        set
        {
            _xValue = value;
            NotifyPropertyChanged();
        }
    }

    private int _yValue;

    public int YValue
    {
        get { return _yValue; }
        set
        {
            _yValue = value;
            NotifyPropertyChanged();
        }
    }

 <StackPanel>
     <ComboBox SelectedIndex="0" Margin="2" Width="100">
        <ComboBoxItem Tag="X">X</ComboBoxItem>
        <ComboBoxItem Tag="Y">Y</ComboBoxItem>
    </ComboBox>

    <Slider Value="{Binding XValue}"></Slider>
</StackPanel>

I want to bind the Slider value to XValue or YValue depending on the selection of the ComboBox

You might be better off creating two sliders, if you only want one to be visible you can bind your `Visibility` to your `ComboBox` selection. — Derrick Moeller, Jan 21 '19 at 13:18

score 1 · Accepted Answer · answered Jan 21 '19 at 12:50

You could use a Style with a DataTrigger that binds to the SelectedItem of the ComboBox:

<ComboBox x:Name="cmb" SelectedIndex="0" Margin="2" Width="100">
    <ComboBoxItem Tag="X">X</ComboBoxItem>
    <ComboBoxItem Tag="Y">Y</ComboBoxItem>
</ComboBox>

<Slider>
    <Slider.Style>
        <Style TargetType="Slider">
            <Setter Property="Value" Value="{Binding XValue}" />
            <Style.Triggers>
                <DataTrigger Binding="{Binding SelectedItem.Tag, ElementName=cmb}" Value="Y">
                    <Setter Property="Value" Value="{Binding YValue}" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Slider.Style>
</Slider>

score 0 · Answer 2 · answered Jan 19 '19 at 06:47

I don't think you can change the binding dynamically (in XAML, at least). However, you can do the following:

<StackPanel>
    <ComboBox SelectedIndex="{Binding SelectedIndex}" Margin="2" Width="100">
        <ComboBoxItem Tag="X">X</ComboBoxItem>
        <ComboBoxItem Tag="Y">Y</ComboBoxItem>
    </ComboBox>

    <Slider Value="{Binding SliderValue}"></Slider>
</StackPanel>

The Slider is now bound to another property (SliderValue). Here are the added properties in your view model:

private int _selectedIndex;
public int SelectedIndex
{
    get { return _selectedIndex; }
    set
    {
        _selectedIndex = value;
        NotifyPropertyChanged();

        if (SelectedIndex == 0)
            SliderValue = XValue;
        else if (SelectedIndex == 1)
            SliderValue = YValue;
    }
}

private int _sliderValue;
public int SliderValue
{
    get { return _sliderValue; }
    set
    {
        _sliderValue = value;
        NotifyPropertyChanged();

        if (SelectedIndex == 0)
            XValue = SliderValue;
        else if (SelectedIndex == 1)
            YValue = SliderValue;
    }
}

The idea is that when the SelectedItem is changed via the ComboBox, the Slider is updated with either XValue or YValue. When the Slider value is changed, the XValue or YValue is updated depending on the ComboBox selection.

In WPF, I want to dynamically set the itemsource based on combo box selection

2 Answers2