How to use a custom font icon for Expander in Xamarin.Forms (SfExpander)

You can customize the expander header icon with font icons in Xamarin.Forms SfExpander. Please follow the steps below to use the font icons in the Expander Header element.

You can also refer the following article.

https://www.syncfusion.com/kb/11469/how-to-use-a-custom-font-icon-for-expander-in-xamarin-forms-sfexpander

Step 1: Place the ttf file in the shared code project and set the Build action as follows,

Project	Location	Build action
Android	Assets	AndroidAsset
iOS	Resources	BundleResource
UWP	Assets	Content

In addition, add the name of the font file in the info.plist file of iOS project.

<key>UIAppFonts</key> 
<array> 
    <string>ExpanderIcons.ttf</string> 
</array> 

You can also refer to the link below to use custom fonts in Xamarin.Forms.

https://xamarinhelp.com/custom-fonts-xamarin-forms/

Step 2: In ResourceDictionary, define the font to use the custom font as StaticResource.

<ContentPage.Resources>
    <ResourceDictionary>
        <OnPlatform x:TypeArguments="x:String" x:Key="ExpanderIcon">
            <On Platform="Android" Value="ExpanderIcons.ttf#ExpanderIcons" />
            <On Platform="UWP" Value="/Assets/ExpanderIcons.ttf#ExpanderIcons" />
            <On Platform="iOS" Value="ExpanderIcons" />
        </OnPlatform>
    </ResourceDictionary>
    <local:ExpanderIconConverter x:Key="ExpanderIconConverter"/>
</ContentPage.Resources>

Step 3: Bind the FontFamily for Label using resource key. Use converter to display platform specific icons and bind the Device platform using RuntimePlatform to specify the platform in the ConverterParameter. Set HeaderIconPosition as None to hide the default Header icon.

<ContentPage.Content>
        <ScrollView BackgroundColor="#EDF2F5" Margin="{OnPlatform iOS='0,40,0,0'}">
            <StackLayout>
                <syncfusion:SfExpander x:Name="expander1">
                    <syncfusion:SfExpander.Header>
                        <Grid HeightRequest="50">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="70"/>
                                <ColumnDefinition Width="*"/>
                                <ColumnDefinition Width="70"/>
                            </Grid.ColumnDefinitions>
                            <Label HorizontalOptions="Center" VerticalOptions="Center"
                                FontFamily="{StaticResource ExpanderIcon}"
                                Text="{Binding Path=IsExpanded,Source={x:Reference expander1}, Converter={StaticResource ExpanderIconConverter}, ConverterParameter={x:Static Device.RuntimePlatform}}"/>
                            <Label Text="Invoice Date" Grid.Column="1" TextColor="#495F6E"  VerticalTextAlignment="Center" />
                            <Label HorizontalOptions="Center" VerticalOptions="Center" Grid.Column="2"
                                FontFamily="{StaticResource ExpanderIcon}"
                                Text="{Binding Path=IsExpanded,Source={x:Reference expander1}, Converter={StaticResource ExpanderIconConverter}, ConverterParameter={x:Static Device.RuntimePlatform}}"/>
                        </Grid>
                    </syncfusion:SfExpander.Header>
                    <syncfusion:SfExpander.Content>
                        <Grid Padding="10,10,10,10" BackgroundColor="#FFFFFF">
                            <Label BackgroundColor="#FFFFFF" HeightRequest="50" Text="Veg pizza is prepared with the items that meet vegetarian standards by not including any meat or animal tissue products." TextColor="#303030" VerticalTextAlignment="Center"/>
                        </Grid>
                    </syncfusion:SfExpander.Content>
                </syncfusion:SfExpander>
            </StackLayout>
        </ScrollView>
    </ContentPage.Content>

Step 4: Converter to display the platform based icons.

namespace ExpanderXamarin
{
 public class ExpanderIconConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if ((bool)value)
            {
                if ((string)parameter == "Android")
                    return "\ue704";
                else if((string)parameter == "iOS")
                    return "\ue700";
                else
                    return "\ue702";
            }
            else
            {
                if ((string)parameter == "Android")
                    return "\ue705";
                else if ((string)parameter == "iOS")
                    return "\ue701";
                else
                    return "\ue703";
            }
        }
 
        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}

Output