Failed to load AppCompat ActionBar with unknown error in android studio

The solution to this problem depends on the version of the Android support library you’re using:

Support library 26.0.0-beta2

This android support library version has a bug causing the mentioned problem

In your Gradle build file use:

compile 'com.android.support:appcompat-v7:26.0.0'

with:

buildToolsVersion '26.0.0' 

and

classpath 'com.android.tools.build:gradle:3.0.0-alpha8'

everything should work fine now.


Library version 28 (beta)

These new versions seem to suffer from similar difficulties again.

In your res/values/styles.xml modify the AppTheme style from

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">

to

<style name="AppTheme" parent="Base.Theme.AppCompat.Light.DarkActionBar">

(note the added Base.)

Or alternatively downgrade the library until the problem is fixed:

implementation 'com.android.support:appcompat-v7:28.0.0-alpha1'

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