Xamarin Forms Effects

Xamarin Forms Effects are a way to add platform-specific styling to a control in a cross-platform manner. They allow developers to apply effects to elements without subclassing them or creating custom renderers, which makes them a powerful tool when customizing the user interface of a Xamarin Forms app. In this article, we will explore the syntax, example, output, explanation, use, important points and summary of Xamarin Forms Effects.

Syntax

A Xamarin Forms Effect can be defined by subclassing the RoutingEffect class and implementing the following properties and methods:

using Xamarin.Forms;

namespace MyCompany.Forms.App
{
    public class CustomEffect : RoutingEffect
    {
        public CustomEffect() : base("MyCompany.Forms.App.CustomEffect")
        {

        }

        public static readonly BindableProperty PropertyNameProperty = BindableProperty.CreateAttached("PropertyName", 
            typeof(string), typeof(CustomEffect), null);

        public static void SetPropertyName(BindableObject view, string value)
        {
            view.SetValue(PropertyNameProperty, value);
        }

        public static string GetPropertyName(BindableObject view)
        {
            return (string)view.GetValue(PropertyNameProperty);
        }
    }
}

The above CustomEffect class defines an effect with a single property called PropertyName, which can be set on any bindable Xamarin Forms element. The effect can then be attached to this element, and the effect's Apply method will be called when the element is added to the visual tree.

Example

To apply an effect to an element in a Xamarin Forms app, the following CustomEffect class can be used:

using Xamarin.Forms;

namespace MyCompany.Forms.App
{
    public class CustomEffect : RoutingEffect
    {
        public CustomEffect() : base("MyCompany.Forms.App.CustomEffect")
        {

        }

        public static readonly BindableProperty PropertyNameProperty = BindableProperty.CreateAttached("PropertyName", 
            typeof(string), typeof(CustomEffect), null);

        public static void SetPropertyName(BindableObject view, string value)
        {
            view.SetValue(PropertyNameProperty, value);
        }

        public static string GetPropertyName(BindableObject view)
        {
            return (string)view.GetValue(PropertyNameProperty);
        }

        protected override void OnAttached()
        {
            base.OnAttached();

            var view = Element as View;

            if (view != null && !string.IsNullOrEmpty(GetPropertyName(view)))
            {
                view.BackgroundColor = Color.FromHex(GetPropertyName(view));
            }
        }

        protected override void OnDetached()
        {
            base.OnDetached();

            var view = Element as View;

            if (view != null && !string.IsNullOrEmpty(GetPropertyName(view)))
            {
                view.BackgroundColor = Color.Default;
            }
        }
    }
}

This effect sets the background color of a control to a specific color. To use the effect, you first need to add a reference to the CustomEffect class in the XAML code as shown below:

<ContentPage
    xmlns="http://xamarin.com/schemas/2014/forms"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:local="clr-namespace:MyCompany.Forms.App"
    x:Class="MyCompany.Forms.App.MainPage">

    <StackLayout
        VerticalOptions="CenterAndExpand"
        HorizontalOptions="CenterAndExpand">

        <Label
            Text="Custom effect sample"
            FontSize="Large"
            TextColor="Black" />

        <BoxView
            local:CustomEffect.PropertyName="#FF5733"
            HeightRequest="60"
            WidthRequest="60"
            HorizontalOptions="CenterAndExpand"/>

    </StackLayout>

</ContentPage>

Explanation

The CustomEffect class subclasses the RoutingEffect class and is defined in the MyCompany.Forms.App namespace. It contains a PropertyName property, which is a bindable property that can be set on any Xamarin Forms element. The property can be set in XAML as shown above.

The CustomEffect class also overrides two methods: OnAttached and OnDetached. These methods are called when the effect is attached or detached from a control. The OnAttached method sets the background color of the control to the color specified by the PropertyName property. The OnDetached method resets the background color of the control to the default value.

Use

Xamarin Forms Effects can be used to add platform-specific styling or behavior to a control. For example, you can use an effect to customize the appearance of a control by setting its background color, font size, or font family.

Another use case of effects is when you want to add some behavior that is only available on a specific platform, like vibration on a button click, or haptic feedback. You can implement these effects to add these platform-specific behaviors in a cross-platform manner.

Important points

• Xamarin Forms Effects can be used to add platform-specific styling to a control in a cross-platform manner.
• Effects can be applied to a control by setting a bindable property on it.
• Effects are defined by subclassing the RoutingEffect class and implementing the OnAttached and OnDetached methods.
• Effects can be used to add behaviors that are only available on a specific platform.

Summary

Xamarin Forms Effects are a powerful tool for adding platform-specific styling and behavior to a Xamarin Forms control in a cross-platform manner. They are defined by subclassing the RoutingEffect class and implementing the OnAttached and OnDetached methods. Effects can be used to apply behaviors that are only available on a specific platform, as well as to customize the appearance of a control.