MediaElement Control the infromation about currently playing media file audio or video

It really depends on your model: Do you use data binding? The easiest way might be to bind to the SelectedItem property of your playlist and use a Converter:

<AppBarButton Label="Fullscreen" IsEnabled="{Binding ElementName=playlistListBox, Path=SelectedItem.Type, Converter="{StaticResource ContextualConverter}, ConverterParameter=fullscreenIsEnabled}" />

And the Converter:

using System;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Data;

...

    public class SampleConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, string culture)
        {
            switch (parameter as string)
            {
                 case "fullscreenIsEnabled": return ((value as MediaType) == MediaType.Video);//return true for video files
            }
            return null;
        }

        public object ConvertBack(object value, Type targetType, object parameter, string culture)
        {
            throw new NotImplementedException();
        }
    }

happy new year!

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Life is unsure - always eat the dessert first!