I’m coming up to speed on Android development and the distinction between an implicit intent and a broadcast receiver is unclear. I was hoping for help in distinguishing these concepts and when to use the two.
Both receive intents, both react to system messages, so why is a broadcast receiver even needed and when is it used as opposed to an implicit intent and intent filter to accept the implicit intent?
Broadcasts are just that — messages broadcast to anyone listening. They are inherently insecure, and delivery to the intended recipient isn’t guaranteed, because there really isn’t an intended recipient. For example, the
CONNECTIVITY_CHANGE broadcast makes this quite clear: When connectivity changes in an Android device, many apps might be interested. Rather than the
ConnectivityManager having to notify each app via specific
Intent, it sends a broadcast. Any app that has registered interest in this event will be notified. Any app that isn’t running or doesn’t care… won’t.
Intent is “sent” when one app or
Activity wants to launch another to do something very specific. For example, a file-manager might want to launch an image viewer or video player. Your app might want to launch a very specific
Activity within another one of your apps, etc. The communication by specific intents (i.e. including package name and component name) can not easily be intercepted, so it’s somewhat more secure. Most importantly, there’s only and exactly one “receiver” — if none can be found, the
Intent will fail.
BroacastReceiver will be active within an
Service and received broadcasts will generally only change state and/or do minor UI updates… for example, you might disable a few actions if your internet connectivity is dropped. By comparison, a specific Intent will usually launch a new
Activity or bring an existing one to the foreground.
I am going to compile a list here of all the differences between Implicit Intents (sent via
startActivity()) and Broadcasts (sent via
- Broadcasts, by default, can affect multiple applications at once (Ordered Broadcasts have the potential to be disrupted). In contrast, Implicit Intents will only affect one application. Please note that there may be multiple possibilities of applications that could be affected, but eventually only one will be.
- Implicit Intents are handled via Intent-Filters, and Broadcasts are handled via Broadcast Receivers (albeit the intent-filters play a role here too). I have seen in many instances over the web that Broadcasts are compared to Intent-filters and that does not make sense to me.
- An Implicit Intent launches an Activity, or a Service. By contrast, a Broadcast launches a Broadcast Receiver. (This, if you think about it, is the core difference between Intents and Broadcasts. It is because of this reason that Broadcasts aren’t meant to do too much heavy work, and especially not UI work!)
- From the Developers Website:
There is no way for a BroadcastReceiver to see or capture Intents used
with startActivity(); likewise, when you broadcast an Intent, you will
never find or start an Activity. These two operations are semantically
very different: starting an Activity with an Intent is a foreground
operation that modifies what the user is currently interacting with;
broadcasting an Intent is a background operation that the user is not
normally aware of.
I’ll add more if I find anything else.