Question

I have a FlipView with some controls in the DataTemplate. Since it’s in a FlipView, it will generate multiple copies of those controls. If I want to find the control that is in the current FlipView view (i.e. on screen / visible), how can I do it?

I can check the loaded event on the control inside but it will be called multiple times and I won’t know which one is being shown.

Answer 1

Create an Attached Dependency Property that you can bind to the RichTextBlock from the ViewModel, such as:

public static class MyStaticClass
{
    public static readonly DependencyProperty IsVisible = DependencyProperty.RegisterAttached("IsVisible", typeof(bool), typeof(MyStaticClass), new PropertyMetadata(false, OnVisibilityChanged));

    private static void OnVisibilityChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var rtb = (RichTextBlock)d;
        var isVisible = (bool)e.NewValue;

        // Do something to rtb.Inlines  
    }
}

With this property, you can bind it to the ViewModel’s IsSelected property:

<FlipView ItemsSource="{Binding SomeList}" SelectedItem="{Binding SelectedVM, Mode=TwoWay}">
    <FlipView.ItemTemplate>
        <DataTemplate>
            <RichTextBlock ns:MyStaticClass.IsVisible="{Binding IsSelected}" />
        </DataTemplate>
    </FlipView.ItemTemplate>
</FlipView>

When the SelectedItem is changed, you can set IsSelected on the child View Model to true, and that triggers the MyStaticClass.OnVisibilityChanged event.