Developing Reusable Cross-Platform Plugins for Xamarin

Alan Grgic

@spellgrgicright

code-sharing techniques for creating universal packages

A Little About Me

Sharing is Caring

Why do we love Xamarin?

Xamarin API Landscape

Platform-Specific APIs

Commonalities in Platform-Specifics

- Vibration

- GPS

- Accelerometer

- Local File System

- Battery Info

- Flashlight

- Phone Dialer

- etc.

The Missing Piece?

Shared Non-UI SDK Functionality.

Platorm-Specifics

Xamarin

netstandard

A Review of Some Abstraction Techniques

- Service Locator Pattern
 

- Factory Pattern

Service Locator Pattern

Service Locator Example

Factory Pattern

Factory Pattern Example

We want our code to be reusable in packages across projects though...

Plugin Architecture

- Move all the plugin logic into separate projects

- Platform-specific projects contain only sdk code

- Plugin.Shared is referenced by all other projects

- PluginImpl implements the IPlugin interface

- CrossPlugin is a singleton factory of PluginImpl

Plugin Example

How Can this Possibly Work?

Look closely... Platform Code is never referenced directly!

Native SDK

netstandard business logic

netstandard plugin

???somehow native sdk code executes???

Rules for Creating Xamarin Plugins

• Everything callable from shared code uses the same namespace
   
• All assemblies have the same name
   
• All assemblies have the same version number

The "Bait and Switch" technique

- The netstandard project of your plugin is never actually executed.

- By adding a reference to the platform-specific library, the netstandard output project gets overwritten (switched) at build time since we made the two assemblies have the same name and version number!

Packaging for NuGet

- Create a nuspec file that describes our deliverables and dependencies

- Bundle the netstandard dll and each platform dll all together in one pkg

- Each dll is only installed to its corresponding target platform

- Need to install the NuGet pkg on all projects

- From that point, the "Bait and Switch" trick takes over

Anatomy of a nuspec file

Xamarin.Essentials

- One library that contains several common plugins in one pkg
 

- Linking/tree shaking removes unused plugin code from builds
 

- Currently in preview and active development
 

- Source: https://github.com/xamarin/essentials
 

- Documentation: https://docs.microsoft.com/en-us/xamarin/essentials

Developing Reusable Cross-Platform Plugins for Xamarin

Alan Grgic

@spellgrgicright

Thanks!