Programming, Xamarin.Forms, Xamarin.Forms.Android

Obtaining a Google Maps API Key

I recently observed an issue when debugging my Xamarin.Forms.Android solution which uses Xamarin.FormsMaps in two different development environments.

The problem was, that I received an error stating that I was missing authentication with the Google Maps API in only one development environment.

Solving the issue

This guide assumes that you have already succesfully established a connection with the Google Maps API in at least one development environment. If you havn’t already worked with Xamarin.FormsMaps before, here is a guide on how to get started, and here is a detailed list of the required permissions in your Android project.

Anywho, on to the issue at hand:

  1. First, obtain the SHA1 fingerprint from your debug key by following this guide
    1. While you’re at it, grab the SHA1 fingerprint for your release key as well by following the same process, but by select the certificate you use for release
  2. Open the Google Developers Console
  3. Select your project and navigate to “APIs & auth” => “Credentials”
  4. In here, click “Edit allowed Android applications”
  5. For each key you have (I’ve got 3 in total: 2 development enviroments, and 1 release certifcate) add a new line with the following contents:
    1. <SHA1-fingerprint>;com.your.packagename
  6. Click “Update”

By now, your “Key for Android applications” should resemble that of the screenshot below. If it does, the Google Maps API has been succesfully registered with both your development and release certficates.

Android SHA1 Fingerprints

Android SHA1 Fingerprints

// Dave


Resolving “Compile to dalvik: Unexpected top-level error” under Xamarin.Android

If you are using the following configuration under Xamarin.Android, you may experience an issue (Compile to dalvik: Unexpected top-level error) which prevents your build from succeeding:

  • Xamarin.Forms
  • Xamarin.Forms.Maps
  • Deploying to release

Resolving the issue

To resolve this issue, simply do the following:

  1. Right-click on your Xamarin.Android project
  2. Select “Properties”
  3. Open “Android Options” => “Advanced”
  4. Set “Java Max Heap Size” to 1G

Now, you should be able to build your Xamarin.Android project in release mode once more.

// Dave


Json.NET crashes when releasing an Xamarin.Android Application

So, after I published my last post, some users reported that the Android app I’m developing didn’t contain any content.

This seemed weird to me, as I knew for a fact, that the iOS version worked just fine.

Fortunately, I am using Xamarin.Insights, which allows me to monitor issues that may arise.

Apperently, the users whom had installed the Android app experienced a lack of content due to a JSON serialization issue which meant that no data was shown – ofcourse, this should be handled by presenting an error message in the UI as well.

The reason was, apparently, that Json.NET crashes in release mode under Xamarin.Android, but not when debugging, which is why I didn’t initially experience the issue myself.

The solution

What you need to do if you experience this issue is to follow these simple steps:

  1. In Visual Studio / Xamarin Studio, right click on your Android project and select “Properties”
  2. Go to “Android Options” => “Linker”
  3. In the field “Skip linking assemblies” enter “System.Core” (without the quotes)
    1. Note: if you have already omitted other assemblies, seperate them using “;” (quotes omitted)
  4. Save

Now, you can release your Android app once more without having Json.NET crashing.’

Testing the solution

If you want to be sure that the solution works before publishing your app to the Google Play Store, you can:

  1. Set your “Solution Configuration” to “Release”
  2. In Visual Studio, open the “Debug” menu
  3. Now click “Start Without Debugging”

Doing so allows the application to be installed in release-mode on your emulator/device.

// Dave


Publishing Xamarin.Forms.Android Application to Google Play

So, I recently had to publish a Xamarin.Forms.Android Application to Google Play. I experienced a few bumps along the way, but finally succeeded this very evening.

Preparing the .APK

First of all, you want to make sure that you disable debugging, specifiy an application icon, version the application and configure your linker.

Afterwards, you’ll need to build the package in Release mode. No problem, right?

Well, I personally experienced a “COMPILETODALVIK : UNEXPECTED TOP-LEVEL” error while doing so, which, apparently was related to Xamarin.Forms.Maps.

If you experience this issue, it can either be due to missing permissions in your Android Manifest or the Heap Size. This is all explained in the previous forum discussion.

After resolving the error, I was finally able to clean & rebuild the solution.

Signing the .APK

Now, for signing the .APK, instead of using the command line tools, you can simply use the tools provided in Visual Studio.

Simply navigate to “Tools” –> Android” –> “Publish Android App…” in the Visual Studio menu, and select “Create new keystore”.

After you have created your keystore, select where you want your signed .apk to be built to and click “Publish”.

Publishing the .APK

Now, in your “bin/Release” folder, you will have two .apk files generated.

So, here I was, thinking to myself, that I could simply upload the signed version of the .APK.

But alas, when I tried to do so, I was told (no matter what I did) that the .APK was, to my amazement, not zipaligned correctly.

I also did try to upload the aligned .APK which was generated from the publishing process, but to no avail.

So, before I was able to publish, I needed to zipalign the signed version of the .APK.

So, what I did was to grab a copy of the .APK which said “Signed” under “bin/Release”.

I then navigated to where my Androd SDK was located, and jumped into “android-sdk\build-tools\<version>” and for ease, pasted my .APK here.

Note: if you are unable to locate this folder, you probably havn’t insstalled the build tools. You can install the build tools in Visual Studio under the Android SDK Manager.

I then popped open a terminal and navigated to the build tools folder, and typed in the followng command (I, ofcourse, replaced “helloworld” with the name of my application):

Afterwards, I was finally able to upload my .APK to the Google Play Store.


// Dave