Xamarin.Forms: How can I load ResourceDictionary from another file?

Question

I wrote following code, but XamlParseException has bean thrown. ("StaticResource not found for key CustomColor")

MyPage.xaml

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="XFApp11.MyPage">
    <ContentPage.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="CustomResource.xaml" />
            </ResourceDictionary.MergedDictionaries> 
        </ResourceDictionary>
    </ContentPage.Resources>

    <ContentPage.Content>
        <BoxView Color="{StaticResource CustomColor}" />
    </ContentPage.Content>
</ContentPage>

CustomResource.xaml (build action = EmbeddedResource)

<?xml version="1.0" encoding="UTF-8" ?>
<ResourceDictionary xmlns="http://xamarin.com/schemas/2014/forms"
                    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml">
    <Color x:Key="CustomColor">#004B86</Color>
</ResourceDictionary>

Answer 1

From Xamarin.Forms 3.0 MergedWith has been deprecated and should not be used.

Now you can use either Source or MergeDictionaries.

MyResource.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ResourceDictionary xmlns="http://xamarin.com/schemas/2014/forms"
                    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
                    x:Class="UI.MyResource">
    <Style TargetType="Label">
        <Setter Property="TextColor" Value="Blue" />
    </Style>
</ResourceDictionary>

So, if MyResource.xaml is in the same assembly you can use directly:

<?xml version="1.0" encoding="utf-8" ?>
<ResourceDictionary xmlns="http://xamarin.com/schemas/2014/forms"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    x:Class="UI.AnotherResource"
    Source="MyResource.xaml">
</ResourceDictionary>

Otherwise (MyResource.xaml is on another assembly):

<?xml version="1.0" encoding="utf-8" ?>
<ResourceDictionary xmlns="http://xamarin.com/schemas/2014/forms"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:otherresources="clr-namespace:OtherAssembly.UI.Resources"
    x:Class="UI.AnotherResource">
    <ResourceDictionary.MergedDictionaries>
        <otherresources:MyResource />
    </ResourceDictionary.MergedDictionaries>
</ResourceDictionary>

Some things to take into consideration:

• Source: It can only be used in XAML, and the value is the path to the xaml file (always in same assembly)
• MergeDictionaries: It can be used regardless of the assembly where the resource reside

More info in Xamarin Forms Resource Dictionaries