Retrieve Value from a User control using Dependancy property (UWP) - xaml

Question

I have a custom user control like this
<Grid>
<ListView x:Name="LView" SelectedIndex="{Binding SelectedIndex}" ItemsSource="{x:Bind
ItemsSource, Mode=OneWay}" Width="{x:Bind Width}" Height="{x:Bind Height}" VerticalAlignment="Stretch" SelectionMode="Multiple" />
</Grid>
Now in Codebehind, I am trying to get its SelectedIndex using a dependency property
public int SelectedIndex
{
get { return (int)GetValue(SelectedIndexProperty); }
set { SetValue(SelectedIndexProperty, value); }
}
public static readonly DependencyProperty SelectedIndexProperty =
DependencyProperty.Register("SelectedIndex", typeof(int), typeof(CustomControl), new PropertyMetadata(0));
And In my main page, I am accessing that dependency property like this
<local:CustomControl Grid.Column="0" Grid.Row="0" Width="400" Loaded="EditTextControl_Loaded"
x:Name="MultiCombo" ></local:CustomControl>
Codebehind
var selIndex = MultiCombo.SelectedIndex;
but neither an event is getting fired on the selectedIndexChange (in the main page) nor I am getting any value on my main page. How can I make this happen?
Note: I have uploaded complete code here

Answer 1

In your CustomControl page, the mode you bind the SelectedIndex property of ListView with SelectedIndex dependency property is OneWay, when you select other items in ListView, the SelectedIndex dependency property won't change, so the value of MultiCombo.SelectedIndex in main page won't change. In this case, you need to set the mode as TwoWay.
CustomControl.xaml:
<ListView x:Name="LView" SelectedIndex="{x:Bind SelectedIndex,Mode=TwoWay}" ItemsSource="{x:Bind ItemsSource, Mode=OneWay}" Width="{x:Bind Width}" Height="{x:Bind Height}" VerticalAlignment="Stretch" SelectionMode="Multiple" />
In your main page, you subscribe the DataContextChanged event to get the SelectedIndex dependency property, but this event only occurs when the DataContext of current page changes. If you want to trigger method in your main page when the selected index of ListView changes, you can define a dependency property in your main page to bind with the SelectedIndex dependency property of CustomControl and add a static callback method that is automatically invoked whenever a property value change is detected. For example:
MainPage.cs:
public int MPSelectedIndex
{
get { return (int)GetValue(MPSelectedIndexProperty); }
set { SetValue(MPSelectedIndexProperty, value); }
}
public static readonly DependencyProperty MPSelectedIndexProperty =
DependencyProperty.Register("MPSelectedIndex", typeof(int), typeof(MainPage), new PropertyMetadata(0, new PropertyChangedCallback(OnDataChanged)));
private static void OnDataChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
MainPage currentPage = d as MainPage;
int count = currentPage.MultiCombo.SelectedIndex;
}
MainPage.xaml:
<local:CustomControl Grid.Column="0" Grid.Row="0" Width="400" Loaded="EditTextControl_Loaded" x:Name="MultiCombo" SelectedIndex="{x:Bind MPSelectedIndex,Mode=TwoWay}" >
</local:CustomControl>
Note:
Since you set the SelectionMode of ListView is Multiple, when you select the first item, the SelectedIndex is 0 and then you also select the second item, the SelectedIndex is still 0. Only when you unselect the first item, the SelectedIndex will change and the method will be triggered.

Answer 2

I think the issue is that you are not binding the SelectedIndex properly.
Instead of binding to self/ ListView's SelectedIndex, you need to bind it to the CustomControl's SelectedIndex DependencyProperty.
<ListView ... SelectedIndex="{Binding
Path=SelectedIndex,
Mode=TwoWay,
RelativeSource={RelativeSource
Mode=FindAncestor,
AncestorType={x:Type UserControl}}}" .../>
You might need to change the type to your CustomControl's type as necessary (if it is not UserControl).