Romman Sabbir
Romman Sabbir | Official

Romman Sabbir | Official

Dependency Injection (Android): Implementation with Examples (Hilt) [PART 3]

Dependency Injection (Android): Implementation with Examples (Hilt) [PART 3]

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Romman Sabbir
·Sep 30, 2022·

2 min read

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Table of contents

Examples

Before you get started with the examples, check out PART 1 and PART 2

Install Hilt on Application

  • Add dependencies
  • Annotate YouApplicationClass with @HiltAndroidApp
  • Code:
@HiltAndroidApp
MyApplication : Application()

To Provide Dependency to Activity/Fragment

  • To @Inject any object to Activity or Fragment, we need to annotate Activity or Fragment with @AnroidEntryPoint
  • Code:
@AndroidEntryPoint
SampleActivity : BaseActivity(){
      @Inject
      lateinit var somethingObject : SomethingObject
}

To Provide Dependency to ViewModel

  • To @Inject any object to ViewModel, we need to annotate ViewModel with @HiltViewModel and @Inject the constructor.
  • Code:
@HiltViewModel
SomethingViewModel @Inject constructor() : BaseViewModel(){
      @Inject
      lateinit var somethingObject : SomethingObject
}

ViewModel Constructor Injection

  • To @Inject objects to ViewModel, we need to annotate ViewModel with @HiltViewModel and @Inject the constructor.
  • Code:
@HiltViewModel
SomethingViewModel @Inject constructor
(private val somethingObject : SomethingObject) 
: BaseViewModel(){...}

Provide Foreground Activity Context to any Injectable Class

  • To provide ActivityContext to any Injectable Class, @Inject class constructor and annotate context with @ActivityContext and register in ActivityComponent module to provide the Context.
  • Code:
// Lets see how to inject a custom dialog object to an activity or fragment

// First, create a CustomDialog class and inject the constructor with Context object
class CustomDialog @Inject constructor(@ActivityContext private val context : Context){....}

// Second, Register the CustomDialog to any ActivityComponent module
@Module
@InstallIn(ActivityComponent::class)
object ActivityModule{
    @Provide
    fun provideCustomDialog(@ActivityContext context : Context) : CustomDialog = CustomDialog(context)
}

// Third, Inject the CustomDialog to any activity or fragment
@AndroidEntryPoint
class Activity/Fragment : BaseActivity/BaseFragment{
    @Inject
    lateinit var customDialog : CustomDialog
}

How to Inject Interface or Abstract Class

  • To provide an instance of Interface or Abstract Class to any dependent object, we can't directly inject any interface or abstract class becuase there is no way to initialize interface or abstract class. So, we have to provide an Implementation of the interface or abstract class.
  • Code:
// Define an interface
interface SomethingObject{
    fun doSomething()
}

// Define the implementation
class SomethingObjectImpl @Inject constructor() : SomethingObject{
    @override
    fun doSomething(){...}
}

// Register the SomeObject to any *Component module
@Module
@InstallIn(SingletonComponent/ActivityComponent/ViewModelComponent::class)
object SomethingModule{    
    @Provide
    fun provideSomethingObject() : SomethingObject = SomethingObjectImpl()
}

That's it for this series. Happy Coding...

 
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