Update Your Fake AndroidInjector

Using Dagger 2 for dependency injection means that you can inject fake / mock objects for testing. I had been using a fake AndroidInjector to do this in my Espresso tests for an old Android app I was updating, but found that on updating Dagger to a more recent version (from 2.14 to 2.21) the custom AndroidInjector no longer compiled.

The fake AndroidInjector I was using was based on these blogs that were written a couple of years ago:

Another version of that idea can be found here:

This is a quick post on how this can be fixed for anyone who is still using the code from these articles (also a  belated thank- you to these authors for coming up with these ideas).

It Does Not Compile …

The problem came with these internal changes to the Dagger code in version 2.19.


Simple Fixes

Based on the code from the articles mentioned above, just need some simple changes (that unfortunately took me a while to work out!).
1. Replace the deprecated annotation




2. The generic typing for AndroidInjector.Factory and other classes used in the AndroidInjector code have changed from

<? extends Activity> // java
<out Activity> // kotlin


<?> // java
<*> // kotlin

3. The DispatchingAndroidInjector  has changed it’s  constructor signature. Instead of having a single parameter of a Map of the Provider  of the AndroidInjector.Factory keyed by class, there is now an additional parameter of a Map using a String (class name) as the key

So in the Dagger generated code (and in the fake AndroidInjector), the method DispatchingAndroidInjector_Factory.newDispatchingAndroidInjector() also needs this extra parameter (even if just an empty Map).

// java (pseudo-code)

Map<Class<?>, Provider<AndroidInjector.Factory<?>>> classMap = new HashMap<>(1);
// create a custom AndroidInjector.Factory and add it to the provider
Provider<AndroidInjector.Factory<?>> provider = ...
map.put(MyActivity.class, provider);

// empty map to satisfy method signature for newDispatchingAndroidInjector()
Map<String, Provider<AndroidInjector.Factory<?>>> stringMap = new HashMap<>();

return DispatchingAndroidInjector_Factory.newDispatchingAndroidInjector(classMap, stringMap);
// kotlin

val classMap : Map<Class<*>, Provider<AndroidInjector.Factory<*>>> = mapOf(
Pair<Class<*>, Provider<AndroidInjector.Factory<*>>>(T::class.java, Provider { factory }))

// empty map to satisfy method signature for newDispatchingAndroidInjector()
val stringMap : Map<String, Provider<AndroidInjector.Factory<*>>> = emptyMap<String, Provider<AndroidInjector.Factory<*>>>()

return DispatchingAndroidInjector_Factory.newDispatchingAndroidInjector<Activity>(classMap, stringMap)

Why use a fake AndroidInjector?

The more common way to have Dagger inject test dependencies is to maintain a parallel universe of test components and test modules to provide the fake dependencies. This works fine and has the advantages that it shouldn’t break due to internal changes in the Dagger code. However it also means more boilerplate code to maintain.


Gradle Dependencies for Java, use compile or implementation?

While I was explaining to a colleague about using Gradle for Java projects (he was moving away from Maven), we came across various code samples. Some of the examples were using the compile configuration for dependencies, while others were using implements and api.

dependencies {
compile 'commons-httpclient:commons-httpclient:3.1'
compile 'org.apache.commons:commons-lang3:3.5'

dependencies {
api 'commons-httpclient:commons-httpclient:3.1'
implementation 'org.apache.commons:commons-lang3:3.5'

This post was a summary based on the documentation and StackOverflow questions to explain to him which configurations to use.

New Dependency Configurations

Gradle 3.4 introduced the Java-library plugin, which included the then new configurations implementation and api (amongst others). These were meant to replace the compile configuration which was deprecated for this plugin. The idea was that the new configurations would help to prevent leaking of transitive dependencies for multi-module projects.

Please note that in this post I am just using the compile vs implementation/api configurations as an example. Other new replacement configurations were introduced as well, please read the documentation for further information.


For a Java project using Gradle 3.4+, then it depends on whether you are build an application or a library.

For a library project or a library module in a multiple module project, it is recommended to use the Java-library plugin, so in build.gradle use this

apply plugin: 'java-library'

instead of

apply plugin: 'java'

Then you would use either implementation or api, depending on whether you want to expose the dependency to consumers of the library.

For a plain application project, you can stick with the java plugin and continue to use the compile configuration. Having said that, I have tried using the Java-library plugin for an app project and it seems to work fine.


For an Android project, the new configurations came with the Android Gradle Plugin 3.0. So unless you are still using the 2.x version of Android Studio / Android Gradle plugin, the use of compile is deprecated. So you should use implementation, even for an app.

In fact, when I recently upgraded my Android Studio, it came up with the message:

Configuration ‘compile’ is obsolete and has been replaced with ‘implementation’.
It will be removed at the end of 2018

I think this also applies if you use Kotlin instead of Java.


How about a project with Groovy as well as Java? This can be for a mixed Groovy / Java project, or for a Java project which needs Groovy for some support tools (such as Spock or Logback configuration).

In the past I have used the Groovy plugin instead of the Java plugin for mixed projects. The Groovy plugin extends the Java plugin and will handle the compilation for Java sources as well as Groovy sources.

apply plugin: 'groovy'

You can continue to do this for Java application modules, but the documentation states that the Groovy plugin has compatibility issues with the Java-library plugin so will need a work around for library modules.

Of course this short post is for newbies, and has only scratched the surface in terms of learning about all the new dependency configurations.