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XAML Markup Extension

The XAML markup extension adds additional functionality thats not defined in the standard XAML spec.

x:Static

The x:Static extension can be used to access any one of the following from XAML:

  • a public static field
  • a public static property
  • a public constant field
  • an enumeration member

Referencing static fields

We can reference any static fields, whether from the .net framework or our own code. In the sample below we will reference a static field from our own class :

MonthsPage.cs

namespace LayoutSample
{
    public partial class MonthsPage : ContentPage
    {
        public static string[] Months = new[]{
                "January",
                "February",
                "March",
                "April",
                "May",
                "June",
                "July",
                "August",
                "September",
                "October",
                "November",
                "December"
            };

        public MonthsPage()
        {
            InitializeComponent();
        }
    }
}

MonthsPage.xaml.cs

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage 
    xmlns="http://xamarin.com/schemas/2014/forms" 
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
    xmlns:local="clr-namespace:LayoutSample"
    x:Class="LayoutSample.MonthsPage">
    <ContentPage.Content>
        <ListView ItemsSource="{x:Static local:MonthsPage.Months}" />
    </ContentPage.Content>
</ContentPage>

Note

To refer to the static member, Months we first have to define the namespace in which the member is found. We define the namespace as follows xmlns:local="clr-namespace:LayoutSample".

We can now use the x:Static extension to refer to the static property Months defined in the MonthsPage.

Add a blank space to a label

We are going to use the Environment.NewLine defined in the System class to add a newline to the contents of the label.

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage 
    xmlns="http://xamarin.com/schemas/2014/forms" 
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
    xmlns:sys="clr-namespace:System;assembly=mscorlib"
    x:Class="DataBindingDemo.SharedResources.MarkupExtensionPage">
    <ContentPage.Content>
        <Label>
            <Label.FormattedText>
                <FormattedString>
                    <Span Text="I am the first line" />
                    <Span Text="{x:Static sys:Environment.NewLine}" />
                    <Span Text="{x:Static sys:Environment.NewLine}" />
                    <Span Text="am separated by a new line" />
                </FormattedString>
            </Label.FormattedText>
        </Label>
    </ContentPage.Content>
</ContentPage>

We define the namespace for System using the xmlns:sys="clr-namespace:System;assembly=mscorlib". Since the property NewLine is static, we can use it in the Span with x:Static extension by using <Span Text="{x:Static sys:Environment.NewLine}" />.

StaticResource Markup Extension

The StaticResource is XAML markup extension is used to retrieve objects defined in the ResourceDictionary.

We can use the ResourceDictionary to keep arbitrary objects referenced by a key. In the following example, we define a color resource and double resource. We use the keys when defining the resources. We can then later on use the StaticResource to retrieve the object by the key.

    <ContentPage.Resources>
        <ResourceDictionary>
            <Color x:Key="ColorPrimary">#ff9900</Color>
            <x:Double x:Key="BorderSize">1</x:Double>
        </ResourceDictionary>
    </ContentPage.Resources>

Use the color resource defined as follows :

<Button 
    Text="Login" 
    BorderColor="{StaticResource ColorPrimary}" 
    BorderWidth="{StaticResource BorderSize}" />

Platform Specific Keys

We can define keys that should be only be available on a specific platform using the OnPlatform. Since the OnPlatform is a generic object, we will need to specify the x:TypeArguments.

<ResourceDictionary>
    <OnPlatform 
        x:Key="PaddingiOS" 
        x:TypeArguments="Thickness" 
        iOS="0,20,0,0" />
</ResourceDictionary>

The object will only be available on iOS, and we can use it the same way.

<StackLayout Padding="{x:StaticResource PaddingiOS}">  
</StackLayout>

Accessing the Resources in Code

We can access the objects defined in the ResourceDictionary by accessing them using the Resources property. Since its a dictionary, we can use the key to retrieve the object.

<Application xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="DataBindingDemo.App">
    <Application.Resources>
        <ResourceDictionary>
            <Color x:Key="ColorPrimary">#CC0033</Color>
        </ResourceDictionary>
    </Application.Resources>
</Application>

We have defined a color in the application resources. The resources defined in the application resources will be available anywhere in the app. We can use both XAML or code to access them.

Let's retrieve the color and apply it to navigation bar :

MainPage = new NavigationPage(new MainTabsPage())
{
    BarBackgroundColor = (Color)Resources["ColorPrimary"],
    BarTextColor = Color.White
};

Since we know the resource object is type color, we were bold as cast it to the Color class.

DynamicResource XAML Markup Extension

The DynamicResource extension is similar to the StaticResource extension with one difference, it maintains a reference to the object. If the resource changes, then the updates are reflected.

If we have the following in the resource dictionary :

<ResourceDictionary>
    <x:String x:Key="CurrentDate">Will show a date if accessed dynamically</x:String>
</ResourceDictionary>

and then use the StatiResource and DynamicResource to access the same key, you will notice that the one accessed using the DynamicResource will update since we have a timer running every second :

<Label Text="{StaticResource CurrentDate}" />
<Label Text="{DynamicResource CurrentDate}" />

and in code we update the resource :

Device.StartTimer(TimeSpan.FromSeconds(1), () =>
{
    Resources["CurrentDate"] = DateTime.Now.ToString("hh:mm:ss");
    return true;
});