fbpx
billiger.de Mobile App Case Study

billiger.de Mobile App Case Study

Arne Jans

Arne Jans

Software Developer, solute

Vivien: Hi Arne, great to talk with you today. Let’s get started by learning more about you and billiger.de.

Arne: Hi Vivien. I’ve been doing software development for more than 10 years, and API design for the last 5 years. I am currently responsible for mobile development for billiger.de, the most widely used and award-winning price comparison portal in Germany. We’re especially proud of our data security, which was just recently awarded too.

The company behind billiger.de is solute GmbH, which is based in Karlsruhe. They also have a few other brands: shopping.de, an online shopping platform for men and women, and friends communication, an online marketing agency. At billiger.de we’re about 150 employees.

Some of our stats:

300,000+

active daily users on billiger.de

500,000+

app downloads

70 Million

prices in the database

22,500 Shops

comparing 1M products

So clearly, the database and its performance on the server side is very important. Companies update their prices all the time, and on top there are all kinds of vouchers that can be applied. All of these are changing frequently – and you never know who updates their prices when. So, you can see the challenges – from a technical standpoint but also for consumers. It is hard to get the best price.

V: Tell me more about the billiger.de app – why did you decide to go for a native app?

A: Well, to be honest there was an existing native app when I came into the company. But aside from that, it’s essential for UX. We also need some offline capability for features like the notepad function or when users are in the store without an Internet connection and scan barcodes. Once they are online again, the query goes to the cloud – and the user gets his result.

V: So are most of your users on the app? Or rather web?

A: We definitely still have more web users, but user numbers are shifting to mobile more and more. Also, our web users are often one time users only. Our loyalty rate is much higher with app users, so we are trying to increase app installs. We’re seeing that – even on the web – the majority of users are coming from mobile devices. Therefore, we relaunched the website a couple of years ago to be responsive and mobile optimized. So we are focusing more and more on mobile, on both the website and through the app. 

V: Why did you need to implement a local database? How is it implemented in your solution?

A: We need data persistence mainly for certain features. We’re still using SQLite, but it’s too much boilerplate code and too little fun. We have been using an ORM on top of SQLite until recently, but it didn’t work well in combination with Proguard on some Android versions anymore. So it resulted in lost data. We’re currently using ObjectBox in the billiger.de Pro version and in a fun new project called PricePretzel, which gives users the best price actively and tracks savings. In these projects, ObjectBox has proven its worth, so we want to migrate the billiger.de app too. 

V: Yes, SQLite with an ORM can get very messy. So, why did you choose ObjectBox as the alternative?

A: I looked at several SQLite alternatives and ObjectBox looked interesting. The main decision factors were: ease of integration, stability, and performance. But ease of use and integration were really the most important factors. Stability and enough performance were rather basic necessities. We found ObjectBox really easy to use – we did the migration and everything and because ObjectBox handles that automatically, it was really simple.

We found ObjectBox really easy to use – we did the migration and everything and because ObjectBox handles that automatically, it was really simple.

V: So did performance matter to you at all?

A: For our needs, performance was secondary. Obviously the performance needs to be good enough, but we do not have super high requirements regarding performance.

V: Do you do any sort of synchronization

A: Synchronization obviously is a super interesting feature and we are keeping an eye on it once it is publicly released. From the setup we have, we would need to do it with a connector to our existing database. Currently the web data and app data are separated and we are working on integrating them. So, this needs synchronization. 

V: Which other tools do you use in your solution/are you excited about?

A: Retrofit from Square, a networking library, we recommend it to everyone and it works super well with ObjectBox. Both libraries work well together with our business objects. Retrofit fetches the fresh data from our servers and deserializes it into our business objects, which are then persisted with ObjectBox without any additional boilerplate code.

V: billiger.de has over 500.000 downloads and about 4 stars on average – how many daily users does the billiger.de app have? Do you have peak times?

A: Obviously holidays like Christmas and Easter are busier. During the day, early evenings get the most traffic – about 1000-2000 daily active users in the billiger.de app, 200 in our Pro-app, and iOS is similar. As I shared before, we get about 300k daily users on the website.

V: Thanks for sharing, and for talking with me today. Any last words?

A: Thank you for having me! I am looking forward to do more with ObjectBox and am very excited about what comes next!

App Bundle and Sideloading: how to prevent crashes

App Bundle and Sideloading: how to prevent crashes

Sideloading can cause crashes when used with Android App Bundle. Google is pushing Android developers to publish their apps to Google Play using the new Android App Bundle format. While it comes with benefits, it can also cause your app to crash, if users sideload your app. We’ll explore why this happens and how to fix it.

Android App Bundle (AAB) enables smaller app downloads and updates, increasing the chances that more people will install your app. Developers benefit as well by only having to build a single artifact instead of multiple APKs tailored to various types of devices.

App Bundle and Sideloading

The Play Store will take care of installing the right set of split APKs from the App Bundle for each user’s device configuration. But what happens, if users bypass Google Play and sideload the app? Sideloading has been popular (APKMirror anyone?) to get early access to new versions of an app or to not waste expensive data volume on app downloads (relevant e.g. in various parts of Africa and India).

To explain how sideloading can break your app, let’s first have a look at what Google Play would actually install onto a device when you publish an App Bundle. For this we use bundletool, which Android Studio and Google Play also use, to convert an App Bundle to a set of APKs for a specific device. We’ll build an App Bundle for our ObjectBox Kotlin example app and start an emulator running Android Pie (you can connect a real device as well). Then we can run the command:

If we extract the created connected.apks file (e.g. using unzip or 7-Zip) we find three split APKs. A master APK containing the app’s manifest and all of its code. An x86 APK containing the ObjectBox native library. And a xxhdpi APK with some resources specific for the screen density of the emulator device. Depending on your app (if it uses dynamic feature modules or includes translations) and connected device there might be more or less split APKs. But let’s stick with these three.

Out of the three only the master APK can be installed on its own. The others will fail to install. You can try this yourself by dropping the APKs onto an emulator.

Crashing with LinkageError

Now how does this affect sideloading? You can probably already see the issue: due to lack of awareness that you are using the cool new App Bundle format, users only share the master APK. And as mentioned it installs just fine. However, at runtime your app might access a native library like ObjectBox or some density-specific resources. As these are not part of the master APK your app will crash. Bummer.

Detecting and fixing broken installations

But fret not! To make sure your users can enjoy a working app Google provides the Play Core library that can detect incorrect installs (since version 1.6.0). Simply add the dependency:

And add a check in your Application class:

If you do not have an Application class or are using content providers check the full documentation. To see this as part of a working app look at the ObjectBox Kotlin example.

Et voilà, instead of your app crashing users will see a dialog asking them to reinstall the app from the Google Play Store (or “an official store” if the library can’t detect it).

How it works

So how does Play Core know if parts of your app are missing? The library is obfuscated – as most Play libraries are. However, decompiling (just open the class files in Android Studio) allows some basic analysis.

At first, it verifies that the device is API level 21 or higher. Older versions of Android do not support split APKs, so no need to check on these devices.

Then it makes sure that the currently installed version of your app actually requires APK splits. After all, you might still distribute your app as a full blown APK to some devices. This check just looks for a special meta-data manifest tag. This tag is added by bundletool (read Play Store) when converting an App Bundle to a set of split APKs (drop the master APK onto Android Studio and check AndroidManifest.xml).

Now that it is certain your app requires multiple APKs for installation it asks PackageManager for the PackageInfo of your app. Starting with API level 21 this has a splitNames property which has the names of any installed split APKs for your app package. If it is empty one or more APKs were not installed and the user is warned to reinstall the app. Straightforward.

Curiously it also warns you, if there is only one entry with an empty name. Please let us know in the comments why you think that is.

And that is it. Make sure to add the Play Core detection if your app is using ObjectBox and App Bundle to avoid sideloading crashes and keep your users happy.