Dagger inject interface into private fields

Question

I want inject interface implementation in abstract class constructor and use it in child class.

I have compile time errors:

Error:Gradle: Dagger does not support injection into private fields
Error:Gradle: Example.A cannot be provided without an @Provides-annotated method.
Error:Gradle: Example.B cannot be provided without an @Inject constructor or from an @Provides-annotated method.
Error:Gradle: Execution failed for task ':app:compileDemoDebugJavaWithJavac'.
> Compilation failed; see the compiler error output for details.

Example in kotlin.

   object Example {
    interface IData {

        fun foo() {
        }
    }

    class Data : IData {

    }

    @Module
    class DataModel {
        @Provides
        fun data(): IData = Data()
    }

    @Singleton
    @Component(modules =
    arrayOf(DataModel::class)
    )
    interface Injector {
        fun inject(a: A)
        fun inject(b: B)
    }

    val graph: Injector = DaggerInjector.builder().
            dataModel(DataModel()).
            build()

    abstract class A {

        @Inject var data: IData ? = null

        public open fun setUp() {
            graph.inject(this)
        }
    }

    open class B : A() {

        override fun setUp() {
            super.setUp()
            data!!.foo()
        }
    }

    fun bar() {
        val a = B()
        a.setUp()
    }
}

versions:

• com.android.tools.build:gradle:2.1.2
• ext.kotlin_version = '1.0.3'
• compile 'com.google.dagger:dagger:2.4'
• provided 'org.glassfish:javax.annotation:10.0-b28'
• kapt 'com.google.dagger:dagger-compiler:2.4'

---

Here is case. Decompiled java

  public static class A {
  @Inject
  @Nullable
  private Example.IData data;

  @Nullable
  protected final Example.IData getData() {
     return this.data;
  }

  protected final void setData(@Nullable Example.IData <set-?>) {
     this.data = <set-?>;
  }

  public void setUp() {
     Example.INSTANCE.getGraph().inject(this);
  }

}

Answer 1

From the error message, I think the problem is with this line:

@Inject var data: IData ? = null

The backing field for this property is private, and this is what the error says. Usually the lateinit keyword is used for such cases:

@Inject lateinit var data: IData

lateinit is one of several modifiers that expose the backing field directly with the property's access level (public here), making it visible to Dagger-generated classes.