Hello, quick question about the SAM converter and live data : Why do I have to write

liveData.observe(this, Observer { })

when I can write

mediatorLiveData.addSource(liveData) {  }

? In both case, the 2d param of the

observe

or

addSource

is a

android.arch.lifecycle.Observer

and this interface has only 1 method ... I'm confused

I'm puzzled by this too, and ended up writing an extension in a library to get the nicer syntax: https://github.com/LouisCAD/Splitties/blob/master/arch-lifecycle/README.md#observe-and-observenotnull-extension-functions-on-lifecycleowner

Just spitballing, but my guess is it's due to the difference in type parameters. In

MediatorLiveData.addSource

, both the source parameter and the lambda share a generic parameter, while in

LiveData.observe

the generic is only on the lambda. I'm guessing this means that the compiler can infer the generic type on the

MediatorLiveData

method but not the

LiveData

one, so you must use a syntax that specifies it.

See https://stackoverflow.com/questions/46542037/cant-replace-sam-constructor-with-lambda-when-first-argument-is-a-class-with-on