Xamarin and the Magical Quest to Bind a Java Native Library

Hello folks! Did you ever think about how cool it would be to re-use an already working and tested Java library to save a couple of months of development time? Well, you’re not alone. The third-party library ecosystem for Android is vast and had the potential to save app developers a lot of time. Most essential features for an Android application have almost certainly already been coded. Because of this, it is appealing to try and reuse these existing libraries when creating a Xamarin.Android application.

Using JAR Files in Xamarin.Forms

Today, we will be showing you a quick example of how to use a native .jar library in your Xamarin.Forms application! For example, what would you do if you needed to use some methods from the old Joda Time Library in a Xamarin.Forms app? Below are the steps to make that work:

  1. Start by create a small Xamarin.Forms project (the default one is perfect). Add an Android Bindings Library to the Solution. Just like this:
  2. You will see 3 directories in the new project. Download the Joda .jar file from GitHub here. Go to the Jars directory and paste the jar file into it. Then add it to the project. You can have multiple .jar files here, but only a single .aar (you can check this page for more info)
  3. Change the jar file Build Action property to EmbeddedJar. This is important. (If you are binding a .aar file, use the LibraryProjectZip Build Action instead)
  4. Build it!
  5. Whoops! Something went wrong. As you might have expected, there are some differences between both programming languages that need to be resolved manually. If you click on each error, they will show you the objects in the library are missing an implementation, a method, or a whole class. The easiest approach is to remove the properties and methods you know you won’t be using. So, for now, let’s hide them under the rug ;). Each generated object has a “Path” you can use to make the compiler handle that object however you want.
  6. Go to the Metadata.xml file inside the Transforms directory and add a <remove-node path=”<path string generated by the compiler here>”/> for each class that is giving you trouble and rebuild your binding project. Just like this:
  7. Success! Now we’re ready to use our library! Go to your Xamarin.Android project and add a reference to the BindingLibrary project
  8. For simplicity, we will use the library in the OnCreate method of the MainActivity class, but you’re free to create your own helper class to let Xamarin.Forms access your methods. From the Xamarin.Android app we can access the Joda Time Library methods
  9. But, what if we want to use a property that we had to remove in step 6? Well, you need to have some knowledge about the library and the programming language used to build it. Let’s assume we would like to use the DateTime class within the Joda library. Let’s remove the <remove-node> tag for it and try to build it.
  10. In this scenario, the compiler is telling you it can’t build the DLL, because it can’t find any GetValue method to override. Let’s get rid of that method because we won’t be using it. Copy the  path right above the error and use it to add a <remove-node> tag in the Metadata.xml file:
  11. Rebuild your BindingLibrary project and go back to the MainActivity in Xamarin.Android. This time, you should be able to access the DateTime class and it’s methods.

And that’s all, folks! You’ve now referenced a Java JAR library in your Xamarin.Forms app.
If you need further guidance about how to deal with bindings in Android, you can check JonDouglas’s Github here and here for some useful information.
Happy coding!!
 

Related Blog Posts

We hope you’ve found this to be helpful and are walking away with some new, useful insights. If you want to learn more, here are a couple of related articles that others also usually find to be interesting:

Our Gear Is Packed and We're Excited to Explore With You

Ready to come with us? 

Together, we can map your company’s software journey and start down the right trails. If you’re set to take the first step, simply fill out our contact form. We’ll be in touch quickly – and you’ll have a partner who is ready to help your company take the next step on its software journey. 

We can’t wait to hear from you! 

Main Contact

This field is for validation purposes and should be left unchanged.

Together, we can map your company’s tech journey and start down the trails. If you’re set to take the first step, simply fill out the form below. We’ll be in touch – and you’ll have a partner who cares about you and your company. 

We can’t wait to hear from you! 

Montage Portal

Montage Furniture Services provides furniture protection plans and claims processing services to a wide selection of furniture retailers and consumers.

Project Background

Montage was looking to build a new web portal for both Retailers and Consumers, which would integrate with Dynamics CRM and other legacy systems. The portal needed to be multi tenant and support branding and configuration for different Retailers. Trailhead architected the new Montage Platform, including the Portal and all of it’s back end integrations, did the UI/UX and then delivered the new system, along with enhancements to DevOps and processes.

Logistics

We’ve logged countless miles exploring the tech world. In doing so, we gained the experience that enables us to deliver your unique software and systems architecture needs. Our team of seasoned tech vets can provide you with:

Custom App and Software Development

We collaborate with you throughout the entire process because your customized tech should fit your needs, not just those of other clients.

Cloud and Mobile Applications

The modern world demands versatile technology, and this is exactly what your mobile and cloud-based apps will give you.

User Experience and Interface (UX/UI) Design

We want your end users to have optimal experiences with tech that is highly intuitive and responsive.

DevOps

This combination of Agile software development and IT operations provides you with high-quality software at reduced cost, time, and risk.

Trailhead stepped into a challenging project – building our new web architecture and redeveloping our portals at the same time the business was migrating from a legacy system to our new CRM solution. They were able to not only significantly improve our web development architecture but our development and deployment processes as well as the functionality and performance of our portals. The feedback from customers has been overwhelmingly positive. Trailhead has proven themselves to be a valuable partner.

– BOB DOERKSEN, Vice President of Technology Services
at Montage Furniture Services

Technologies Used

When you hit the trails, it is essential to bring appropriate gear. The same holds true for your digital technology needs. That’s why Trailhead builds custom solutions on trusted platforms like .NET, Angular, React, and Xamarin.

Expertise

We partner with businesses who need intuitive custom software, responsive mobile applications, and advanced cloud technologies. And our extensive experience in the tech field allows us to help you map out the right path for all your digital technology needs.

  • Project Management
  • Architecture
  • Web App Development
  • Cloud Development
  • DevOps
  • Process Improvements
  • Legacy System Integration
  • UI Design
  • Manual QA
  • Back end/API/Database development

We partner with businesses who need intuitive custom software, responsive mobile applications, and advanced cloud technologies. And our extensive experience in the tech field allows us to help you map out the right path for all your digital technology needs.

Our Gear Is Packed and We're Excited to Explore with You

Ready to come with us? 

Together, we can map your company’s tech journey and start down the trails. If you’re set to take the first step, simply fill out the contact form. We’ll be in touch – and you’ll have a partner who cares about you and your company. 

We can’t wait to hear from you! 

Thank you for reaching out.

You’ll be getting an email from our team shortly. If you need immediate assistance, please call (616) 371-1037.