Kotlin context as Activity

Question

I came across this in a Kotlin code

val activity = context as Activity

Can someone explain this to me or direct me to the appropriate documentation?

Answer 1

That's a very dangerous piece of code, and likely to be wrong most of the time. In Android every Activity is a Context, Activity is a child class of Context. The reverse is not true- not every context is an Activity. This code is assuming one is and is casting it. If they're wrong in that assumption, it will crash. While this is sometimes an ok thing to do, it is far more common to see it in beginner's code who don't understand exactly what a context is and make mistakes. Treat this as a code smell and be very cautious of code where you see this, it likely comes with an incomplete understanding of what they're doing.

Answer 2

In Android, Context is used as a reference to information about the app, maybe the device, or other types of shared Android level information, this answer here is a good explanation: Context Description

Activities, are a single view within an application, and contain all the tools necessary to render information on a screen.

The code you shared, is saying, take my context and treat it as if it is an object of Activity

There are multiple types of Context in Android, the most common being ApplicationContext, and ActivityContext.

There are times where you need one over the other, but in many cases the ActivityContext is going to be sufficient.

We can cast an ActivityContext to an Activity, and this will allow us to treat the Context as that Activity it came from.

Another reference for more information around Context and Activities in Android would be: Using Context