Tab icons in a Xamarin.Forms UWP TabbedPage? - xamarin.forms

Question

When putting together a TabbedPage in Xamarin.Forms, how do I get UWP to use the page's Icon property?
It looks like UWP could support this just fine, if I configure my Forms attributes/files correctly.
Here's my TabbedPage XAML. The icons are all set up and working for iOS and Android, and even the on-page Image in UWP renders fine (meaning the files are likely in the project correctly).
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:tabbed"
x:Class="tabbed.MainPage">
<TabbedPage.Children>
<local:InitialPage Title="Tab1" Icon="star.png" />
<ContentPage Title="Tab2" Icon="gear.png">
<ContentPage.Content>
<StackLayout>
<Label Text="A nice label." />
<Image Source="star.png" /><!-- works here -->
</StackLayout>
</ContentPage.Content>
</ContentPage>
</TabbedPage.Children>
</TabbedPage>

Answer 1

I outlined how this is possible here http://depblog.weblogs.us/2017/07/12/xamarin-forms-tabbed-page-uwp-with-images/
In short, you need to change the default HeaderTemplate that is being used by UWP. But due to the way Xamarin forms is started, this is not straightforward.
So you need to inject a custom template into the resource dictionary.
Example project is up on Github here https://github.com/Depechie/XamarinFormsTabbedPageUWPWithIcons
Longer detail:
You need to supply your own TabbedPageStyle and switch out the one that Xamarin is using for their UWP rendering.
So the new style contains an Image where we data bind the Source to the Xamarin Icon property.
<Style x:Key="TabbedPageStyle2" TargetType="uwp:FormsPivot">
<Setter Property="HeaderTemplate">
<Setter.Value>
<DataTemplate>
<StackPanel Orientation="Vertical">
<Image Source="{Binding Icon, Converter={StaticResource IconConverter}}" Width="15" Height="15" />
<TextBlock Name="TabbedPageHeaderTextBlock" Text="{Binding Title}"
Style="{ThemeResource BodyTextBlockStyle}" />
</StackPanel>
</DataTemplate>
</Setter.Value>
</Setter>
</Style>
The actual style switching is done in the App.Xaml.cs like this
((Style)this.Resources["TabbedPageStyle"]).Setters[0] = ((Style)this.Resources["TabbedPageStyle2"]).Setters[0];
You'll also need a converter to be sure the Image control understands the Icon source giving by Xamarin
public class IconConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, string language)
{
if (value != null && value is Xamarin.Forms.FileImageSource)
return ((Xamarin.Forms.FileImageSource)value).File;
return null;
}
public object ConvertBack(object value, Type targetType, object parameter, string language)
{
throw new NotImplementedException();
}
}

Answer 2

As it is currently, the UWP TabbedPage renderer does not use the Icon property at all, so getting tab icons will require a custom renderer. Even the official UWP samples don't actually seem to have this baked-in, requiring a custom UserControl.
The Android TabbedPageRenderer and iOS TabbedRenderer, and even the macOS TabbedPageRenderer, use the Icon property to adjust the tab UI, but the UWP renderer would need updating to make this work.