How to generate module consisting @ContributesAndroidInjector in dagger with kotlin?

Question

I am learning dagger 2, right now I am using dagger-2.25.4 on kotlin, I made a BaseApplication class for dagger given below :

package com.example.demomvvm

import com.example.demomvvm.dagger.DaggerAppComponent
import dagger.android.AndroidInjector
import dagger.android.support.DaggerApplication

class MVVMApplication: DaggerApplication() {

    override fun applicationInjector(): AndroidInjector<out DaggerApplication>? {
        return DaggerAppComponent.builder().application(this).build()
    }
}

And here is my AppComponent class:

package com.example.demomvvm.dagger

import android.app.Application
import com.example.demomvvm.MVVMApplication
import dagger.BindsInstance
import dagger.Component
import dagger.android.AndroidInjector
import dagger.android.support.AndroidSupportInjectionModule

@Component(
    modules = [
        AndroidSupportInjectionModule::class,
        ActivityBuilderModule::class
    ]
)
interface AppComponent: AndroidInjector<MVVMApplication> {

    @Component.Builder
    interface Builder{

        @BindsInstance
        fun application(application: Application): Builder

        fun build(): AppComponent
    }
}

My ActivityBuilderModule is not being genrated correctly, here is my ActivityBuilderModule.kt:

package com.example.demomvvm.dagger

import com.example.demomvvm.ui.auth.LoginActivity
import dagger.Module
import dagger.Provides
import dagger.android.ContributesAndroidInjector

@Module
abstract class ActivityBuilderModule {

    @ContributesAndroidInjector
    abstract fun contributeLoginActivity(): LoginActivity

    @Provides
    fun doSomething(): String = "This is a string"
}

This is the error I am getting on Dagger generated code:

/home/suvodip/AndroidStudioProjects/demoMVVM/app/build/tmp/kapt3/stubs/debug/com/example/demomvvm/dagger/AppComponent.java:7: error: [Dagger/MissingBinding] java.lang.String cannot be provided without an @Inject constructor or an @Provides-annotated method.
public abstract interface AppComponent extends dagger.android.AndroidInjector<com.example.demomvvm.MVVMApplication> {
                ^
      java.lang.String is injected at
          com.example.demomvvm.ui.auth.LoginActivity.dagger
      com.example.demomvvm.ui.auth.LoginActivity is injected at
          dagger.android.AndroidInjector.inject(T) [com.example.demomvvm.dagger.AppComponent → com.example.demomvvm.dagger.ActivityBuilderModule_ContributeLoginActivity.LoginActivitySubcomponent]

I am Injecting this here:

package com.example.demomvvm.ui.auth

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.view.View
import dagger.android.support.DaggerAppCompatActivity
import kotlinx.android.synthetic.main.activity_login.*
import javax.inject.Inject

class LoginActivity : DaggerAppCompatActivity(), AuthListener {

    @Inject
    lateinit var dagger: String

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        Log.d("Dagger", "$dagger")

    }
}

Answer 1

@SuvodipMondal welcome to the community.

The error you are getting is because @Binds and @ContributesAndroidInjector methods must be abstract because they don't have method bodies. That means that they must go on an interface or abstract class. @Provides methods may be static, which means they can go on abstract classes and Java-8-compiled interfaces, but non-static ("instance") @Provides methods don't work on abstract classes. This is explicitly listed in the Dagger FAQ "Why can't @Binds and instance @Provides methods go in the same module?"

For achieving this you must have a static function in your abstract class Annotated with @JvmStatic

You must add this.

@Module
companion object{
  @JvmStatic
  @Provides
  fun doSomething(): String = "This is a string"
}

Then your class will become like this.

package com.example.demomvvm.dagger

import com.example.demomvvm.ui.auth.LoginActivity
import dagger.Module
import dagger.Provides
import dagger.android.ContributesAndroidInjector

@Module
abstract class ActivityBuilderModule {

    @ContributesAndroidInjector
    abstract fun contributeLoginActivity(): LoginActivity

    @Module
    companion object{
     @JvmStatic
     @Provides
     fun doSomething(): String = "This is a string"
   }
}

For more reference 1 & 2