The Xamarin platform for building and testing apps catapulted to the forefront of the industry in just a few years to command the attention and ultimate purchase by no less an authority than Microsoft, and the company routinely partners with major corporations that are involved with coding technology. Based on C#, Xamarin.Forms offers developers extraordinary tools for writing code for apps that can shared among iOS, Android and Windows platforms to speed time-to-market, to test app functionality on more than 2,000 devices and to customize controls to give them new capabilities and native user interfaces. Programmers can simplify customizing UIs for each operating system with built-in Xamarin renderers or use custom renderers when the UI requirements can't be designed using simpler tools.

Xamarin.Forms generates UIs that are customized for platforms so that they demonstrate the native abilities and best features of each device. Custom renderers let developers substitute their own instructions to customize the functions and appearance of apps that are made with Xamarin.Forms.

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Creating Custom Controls with Renderers

Using custom renderers expands what creative developers can do and differentiates apps from those of competitors who aren't comfortable customizing app logic with renderers that mimic the look and feel of native apps in cross-platform development. Changing a control or view without a renderer in Xamarin.Forms involves two steps for each platform for which programmers are coding. For example, if changing the default background color from gray to blue, developers would create a custom control or element by changing the subclass information and consuming the custom control instead of the original. The programmers would have to perform this two-step process for each variable.


Benefits of Using Custom renderers in Xamarin.Forms

Custom renderers simplify the process by automatically customizing Labels, ListViews, Buttons and other features for each platform. Although it's not guaranteed that renderer APIs will work in future versions of Xamarin, programmers can update their renderers with relatively simple modifications. Xamarin.Forms uses the same process for rendering platform-specific instructions when developers use the utility to create cross-platform apps. The Xamarin platform has a renderer for each platform that compiles a native UIViewController control and every other app element. For example, when Xamarin.Forms creates a ContentPage, the following platform-specific renderers work in the following way:

  • In Windows Phone, the PageRenderer class instantiates a FrameworkElement control.
  • In iOS applications, PageRenderer class discovers a UIViewController control.
  • In Android, the renderer compiles a ViewGroup control.

This same rendering process can be used by developers to create specific customizations for each app element by creating a Xamarin.Forms page, consuming the page and designing a custom renderer for each platform. The benefits of this approach include:

  • Increasing code-sharing capabilities because the View layer code can be shared
  • Better access to each device's native features
  • Providing developers with the ability to extend existing controls
  • Mitigating performance issues
  • Enhancing native look and feel with native views and controls
  • Enjoying all the Xamarin platform's other intuitive design features such as TestCloud, fantastic support, debugging capabilities and strong documentation of the app development process

Creating Custom Renderers

The process for creating a custom platform renderer works like this:

  • Create a subclass for each element.
  • Override OnElementChanged, which renders the native page, and substitute logic to customize the page.
  • When the Xamarin.Forms control is called, the OnElementChanged method is called.
  • Adding an ExportRenderer attribute specifies that the new logic will be used; otherwise, the OnElementChanged method is called.

Understanding Custom Renderer Limitations

The process of writing custom renderers for each platform can become burdensome for small customizations but saves an incredible volume of coding when the needed changes are extensive. Developers can use their own property implementations for minor changes. Some of the limitations of using custom renderers include:

  • Container classes perform poorly because view measurement invalidation occurs too often.
  • There are performance constraints when XAML views are parsed -- especially when data templating is used.
  • Some features might not be mapped, so developers need to write more extensive code for renderers in these cases.
  • Inexperienced programmers can easily get overwhelmed when working with large applications and multiple renderers.
  • Standard shells limit developers as to what it is possible to do to create complex UIs.

Custom Renderer Classes

Xamarin.Forms offers strong cost-value benefits for developing cross-platform apps, customizing UIs, debugging apps, accessing libraries of resources and collaborating with multiple partners on development projects. The defaults for converting code into platform-specific control classes allow developers to create native performance across feature classes -- for Page, View, Layout and Cell. The renderers -- except for the MapRenderer class -- for each of the following operating systems and their name designations include:

  • iOS: Xamarin.Forms.Platform.iOS
  • Universal Windows Platform: Xamarin.Forms.Platform.UWP
  • WinRT: Xamarin.Forms.Platform.WinRT
  • Windows Phone 8: Xamarin.Forms.Platform.WinPhone
  • Android: Xamarin.Forms.Platform.Android
  • Android (AppCompat): Xamarin.Forms.Platform.Android.AppCompat

When developers need to customize their apps beyond what Xamarin.Forms renderers can achieve, there are two options: adding a custom element that extends the existing instructions and capabilities or adding a custom renderer for each platform. If the changes are small and relatively limited, use the former; if extensive customization is required, adding custom renderers is the better option.


Using Custom Renderers for eCommerce

Differentiation is the key to building an app that eCommerce customers will use on their devices of choice. In today's competitive global markets, designing apps that look and feel native on each customer's device could be the critical difference in winning that customer's business. Market trend analyses predict that B2B eCommerce will surpass sales of $12 trillion by 2020, which more than doubles the $5.5 trillion in sales that involved electronic data exchanges. Mobile eCommerce sales totaled $104.05 billion in 2015, and mobile sales are expected to outpace other shipping methods by 258 percent.[1] Kissmetrics reports that 44 percent of Internet minutes are spent on mobile phones, and an additional 11 percent of total shopping time is done on tablets.[2] Designing apps with Xamarin.Forms and custom renderers has become almost mandatory for eCommerce companies to stay competitive.


Registering Custom Renderers

Building an app that looks and performs like a native and takes advantage of each device's capabilities is the reward of using custom renderers, but there are some additional requirements for application developers. Using the appropriate render kit, developers must register their custom renderers.[3] This allows developers to implement their own renderer classes that can be added to each project. If the effects aren't needed or wanted in other places, developers can use the default behavior for other platforms.


How Clarity Helps with Xamarin App Development

Clarity works like a custom renderer that renders custom renderers in Xamarin.Forms. Our brilliant and experienced team of app development specialists can help you through every step of using the Xamarin platform to build and test apps and to customize UIs for each operating system in cross-platform development. Your can save on app development costs, debug your app and speed distribution to the Apple App Store, Google Play or alternative Android App Stores by sharing large volumes of code. Clarity's functional and responsive website designs can be customized to complement native UIs, and the company's professional support, design team, back-end operations and secure eCommerce programming platform eliminate many operating challenges. Call or contact Clarity today for a free price quote or consultation on Xamarin.Forms app development.
References:
[1] Internetretailer.com: Mobile commerce is now 30% of all U.S. e-commerce www.internetretailer.com
[2] KissMetrics.com: Surprising Mobile Ecommerce Statistics that Will Change the Way You Do Business blog.kissmetrics.com
[3] Docs.oracle.com: Registering a Custom Renderer with a Render Kit docs.oracle.com


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