19. September 2019

Xamarin Visual Studio – Error ADB0020 Android ABI mismatch

Following error message might pop-up when you to run Xamarin app on Android:

Error ADB0020: Android ABI mismatch. You are deploying an app supporting ‘armeabi-v7a’ ABIs to an incompatible device of ABI ‘x86’. You should either create an emulator matching one of your app’s ABIs or add ‘x86’ to the list of ABIs your app builds for.

Here is how you can resolve it.

In Solution Explorer select your project.

Right-click and select Properties or press Alt+Enter.

Select Android Options, scroll down. In right bottom corner click Advanced button.

From the drop down menu select desired architecture, e.g. x86_x64.

Note: After changing any checkbox it is necessary to wait a bit so that Visual Studio syncs the preferences.

Now you should be able to run the project.

8. June 2019

How to add custom mapping of a hostname to IP address in Android Emulator

There is a simple trick which allows your application to resolve a hostname to IP address defined by you even in cases when you do not have access to DNS server. This trick could be also used when you’re connected via VPN and the emulator is not able to resolve DNS record available only in private network.

Let’s add following hostname record which should be resolved by application on Android: test.georgik.rocks

First of all, you need to start your AVD with parameter ‘-writable-system’, because emulator’s filesystem is by default read-only.

Let’s get names of available AVDs.

Example for macOS:

cd ~/Library/Android/sdk/tools
./emulator -avd -list

The output might look like:


Start the emulator:

./emulator -avd "Pixel_2_API_23" -writable-system

You should see the following warning:

emulator: WARNING: System image is writable

The emulator will start. Now you need to remount the filesystem so it will become writable. This could be done via adb tool which is in platform-tools directory.

Version for macOS:

cd ~/Library/Android/sdk/platform-tools
./adb remount

Now you can start the shell and append the line with configuration to /etc/hosts:

./adb shell 'echo " test.georgik.rocks" >> /etc/hosts'

Now you can test the configuration by ping:

root@generic_x86_64:/etc # ping test.georgik.rocks
PING test.georgik.rocks ( 56(84) bytes of data.

7. June 2019

How to solve Android Emulator java.io.FileNotFoundException open failed: EACCES (Permission denied)

Following error in Android application is very annoying and you may waste several hours by hunting the root cause:

D/file: java.io.FileNotFoundException: /storage/emulated/0/Download/20190604_084533.jpg: 
open failed: EACCES (Permission denied)

It might occur even when the manifest is correct and contains proper permission:

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

Here is sample code which will pass on file existence check, but the execution will fail on readBytes:

var file:File = File("/storage/emulated/0/Download/20190604_084533.jpg")
if (file.exists()) {
    val content:ByteArray;
    Log.d("file", "exist")
    try {
        content = f.readBytes()
     } catch (FileNotFoundException) {
        Log.d("file", e.toString())

} else {
     Log.d("file", "does not exist")

To fix this problem it is necessary to go to Settings – Apps – My App – Permission.

Access to Storage is probably disabled. Tap Storage to enable it:

With enabled Storage option, the application was able to read the file.

To solve this problem in a proper way, it’s necessary to add a request for permission to the code. Here is a sample in Kotlin:

if (checkSelfPermission(
    Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
        requestPermissions(arrayOf(Manifest.permission.READ_EXTERNAL_STORAGE), MY_READ_EXTERNAL_REQUEST)

You can find more details about requesting permissions in Android documentation.

23. April 2019

Android Studio Unresolved reference: activity_main – R.layout and R.id

You can easily run into mysterious errors with Android Studio. Here is one.

Suddenly all references related to R.layout or R.id stopped to work and build failed with a message like this:

Compilation error. See log for more details
Unresolved reference: activity_main
Unresolved reference: url_edittext
Unresolved reference: update_button

The code looked like this:

    override fun onCreate(savedInstanceState: Bundle?) {

I tried clean, builds, rebuilds. Nothing helped. The problem was caused by simple import which accidentally occurred in Activity file:

import android.R

After removing this line the whole project was working again and even code hinting was correct.

15. April 2019

Android Emulator application crash: Chromium WebView package does not exist

Android application with WebView might crash with a strange error in Android Emulator:

E/WebViewFactory: Chromium WebView package does not exist
    android.webkit.WebViewFactory$MissingWebViewPackageException: Failed to load WebView provider: No WebView installed
        at android.webkit.WebViewFactory.getWebViewContextAndSetProvider(WebViewFactory.java:334)
        at android.webkit.WebViewFactory.getProviderClass(WebViewFactory.java:398)
        at android.webkit.WebViewFactory.getProvider(WebViewFactory.java:211)

Check the definition of Virtual Device. It’s very likely that your device is using plain Android target which does not contain the WebView. You have to create Virtual Device which contains Google APIs.

Click Create Virtual Device. Select an image with “Google APIs“:

Now you can start the application in the newly created emulator with Google APIs.

The application should run without a problem.