Extension for sharing ViewModels between Activities with Kotlin Koin. (Extensão para compartilhar ViewModels entre activities com Kotlin Koin).

DIExtension.kt

inline fun <retified VM: ViewModel> AppCompatActivity.viewModelShared(): Lazy<VM>  {
    return lazy(LazyThreadSafetyMode.NONE) {
        val scopeKey = this::class.getActScopeId()
        var scope: Scope = getKoin().getOrCreateScope(
            scopeId = scopeKey,
            qualifier = StringQualifier(scopeKey)
        )
        
        lifecycle.doWhen(
            onCreate = {
                scope = getKoin().getOrCreateScope(
                    scopeId = scopeKey,
                    qualifier = StringQualifier(scopeKey)
                )
            },
            onDestroy = {
                if(scope.isNotClosed()) {
                    scope.close()
                }
            }
            
        scope.get()
    }
    
inline fun <retified VM: ViewModel, retified ACTIVITY: AppCompatActivity> AppCompatActivity.sharedViewModel(): Lazy<VM> {
    return lazy(LazyThreadSafetyMode.NONE) {
        val scopeKey = ACTIVITY::class.getActScopeId()
        val koin = getKoin()
        var scope = koin.getScopeOrNull(scopeKey)
        
        if(scope == null) {
            scope = koin.createScope(
                scopeId = scopeKey,
                qualifier = StringQualifier(scopeKey)
            )
            
            lifecycle.doWhen(
                onDestroy = {
                    if (scope.isNotClosed()) {
                        scope.close()
                    }
                }
            )
        }
    }
}

inline fun <retified ACTIVITY: AppCompatActvity> Module.viewModelSharedScope(
    noninline scopeSet: ScopeDSL.() -> Unit
) {
    scope(
        qualifier = named(ACTIVITY::class.getActScopeId()),
        scopeSet = scopeSet
    )   
}


fun Lifecycle.doWhen(
    onCreate: (() -> Unit)? = null,
    onDestroy: (() -> Unit)
) {
    addObserver ( object: LifecycleEventObserver {
        override fun onStateChanged(source: LifecycleOwner, event: Lifecycle.Event) {
            when(event) {
                Lifecycle.Event.ON_CREATE -> onCreate?.invoke()
                Lifecycle.Event.ON_DESTROY -> onDestroy()
                else -> Unit
            }
        }
    })
}

private fun KClass<*>.getActScopeId(): String = "${this.java.simpleName}-SharedActivityScope"

How to use:

// MyKoinModule.kt
viewModelSharedScope<Activity1> {
    scoped {
        MyViewModel ( ... )
    }
}

// Activity1.kt
val viewModel: MyViewModel by viewModelShared()

//  Activity2.kt
val viewModel: MyViewModel by sharedViewModel<MyViewModel, Activity1>()