Customization with Xamarin Custom Renderer

Xamarin Custom Renderer is a powerful architecture used to make platform-specific visual and functional customizations beyond the default controls when developing mobile applications with Xamarin.Forms. Standard Xamarin.Forms controls meet most needs; however, when you want to use all the possibilities offered by platforms or present a custom user interface, the Custom Renderer concept comes into play. In this article, we will examine the concept of Xamarin Custom Renderer in detail and show how to use it with a code sample.

What is Xamarin Custom Renderer?

Xamarin Custom Renderer is a structure used to customize a Xamarin.Forms control specifically for a platform (such as Android, iOS). For each control, we define a renderer class in the relevant platform layer. This way, for example, we can add a special background color, rounded corners, or native features to an Entry control. To write a Custom Renderer, we first define our control on the Xamarin.Forms side and then we write a special class in the platform-specific projects.

Example: Creating a Custom Renderer for the Entry Control

Below, with a simple example, you can see step by step how to write a Xamarin Custom Renderer that paints the background of the Entry control red on the Android side.

1. Creating a Custom Control in Xamarin.Forms

using Xamarin.Forms;

namespace CustomRendererDemo.Controls
{
    public class RedEntry : Entry
    {
        // You can add extra properties here
    }
}

2. Writing the Custom Renderer in Android

using Android.Content;
using CustomRendererDemo.Controls;
using CustomRendererDemo.Droid.Renderers;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;

[assembly: ExportRenderer(typeof(RedEntry), typeof(RedEntryRenderer))]
namespace CustomRendererDemo.Droid.Renderers
{
    public class RedEntryRenderer : EntryRenderer
    {
        public RedEntryRenderer(Context context) : base(context) { }

        protected override void OnElementChanged(ElementChangedEventArgs<Entry> e)
        {
            base.OnElementChanged(e);
            if (Control != null)
            {
                Control.SetBackgroundColor(Android.Graphics.Color.Red);
            }
        }
    }
}

3. Usage

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:controls="clr-namespace:CustomRendererDemo.Controls"
             x:Class="CustomRendererDemo.MainPage">
  <controls:RedEntry Placeholder="Entry with red background" />
</ContentPage>

Conclusion

Thanks to the Xamarin Custom Renderer technique, you can customize the applications you develop with Xamarin.Forms to take advantage of the full power of the platforms. Especially for custom design requirements, integration with native components, or operations requiring performance, Custom Renderer is indispensable. By providing the desired level of control on both iOS and Android, you can develop professional applications and offer unique experiences to your users. Open the way for platform-specific customization with Xamarin Custom Renderer!