ViewModel init call

Hi, I get your sample code for ViewModel

class BackpackViewModel : ViewModel() {
    val backpack: Backpack by inject()
}

and add an initialization block like here

class BackpackViewModel : ViewModel() {
    val backpack: Backpack by inject()
    init {
        backpack.doSomething()
    }
}

But I got this exception

java.lang.IllegalStateException: The dependency has not be injected yet.

If i call backpack.doSomething() after init call everything is working.

How I fix it?

[mrgaric]

I think an example will be enough. thx.

[dlemures]

@afaucogney is right (thx for the answer!), creation happens before injection. The process is divided into 2 steps:

1. When you use installViewModelBinding on your scope, we create the viewmodel using the right APIs under the hood.
2. When you start the injection, for example calling KTP...inject() inside your activity, it’s when we inject the dependencies of the viewmodel.

The issue is that you are trying to access to those dependencies on the first step, when they are not ready yet. This is similar to when you wanna access injected fields inside a constructor. If you are curious, I could explain more about the reasons why we designed it that way.

Nevertheless, there is a way to solve it: using a ViewModel Factory to create the viewmodel using Toothpick.

val scope = KTP.openScopes(xxx)
scope.installViewModelBinding<MyViewModel>(activity, InjectedViewModelProvider(scope))
...

// This provider can be reused for any ViewModel
class InjectedViewModelProvider(private val scope: Scope) : ViewModelProvider.Factory {
    override fun <T : ViewModel?> create(modelClass: Class<T>): T {
        return scope.getInstance(modelClass)
    }
}

class BackpackViewModel(private val backpack: Backpack) : ViewModel() {
    init {
        backpack.doSomething()
    }
}

By doing so, you can use constructor and field injection within your viewmodel.

Same, if you are curious, I can provide more info about why we don’t provide that functionality out-of-the-box.