Android developer portal states broadcasts which can be registered in manifest itself, but it gives a caution as under
Even though these implicit broadcasts still work in the background,
you should avoid registering listeners for them.
One such broadcast which is exempted is as under:
ACTION_LOCKED_BOOT_COMPLETED, ACTION_BOOT_COMPLETED
Exempted because
these broadcasts are only sent only once, at first boot, and many apps
need to receive this broadcast to schedule jobs, alarms, and so forth.
If we should avoid registering them (as per the above caution), then what is the right approach for ACTION_BOOT_COMPLETED ?
Use case: Sync data with the server and show a notification to user (if any)
If you need your app started at boot time, the only way to do this is to have a manifest-registered BroadcastReceiver.
Related
I have a network change receiver class and it extends from broadcast Receiver, but I’m not pretty sure that it’s working in android Oreo, does Oreo support broadcast receiver, and if it doesn’t support, what’s the other way to do it
Oreo supports Broadcast Receivers but with some restrictions on Implicit broadcast that are declared in manifest.
Implicit vs Explicit Broadcast:
According to the documentation, an implicit broadcast is a broadcast that does not target that app specifically. For example, ACTION_PACKAGE_REPLACED is an implicit broadcast, since it is sent to all registered listeners, letting them know that some package on the device was replaced.
However, ACTION_MY_PACKAGE_REPLACED is not an implicit broadcast, since it is sent only to the app whose package was replaced, no matter how many other apps have registered listeners for that broadcast.
So any broadcast receivers that we have defined statically within our application manifest that are listening for implicit broadcasts will no longer receive those broadcasts.
The reason for this change is that implicit broadcasts would previously trigger any component that was listening for them within the manifest— this could have an adverse effect on application and device performance due to large numbers of applications registered to receive specific broadcasts all being triggered at the same time.
But there is a list of exceptions when it comes to implicit broadcasts — this means that there are still some which you can register to receive broadcasts for. They are all listed below:
So if the broadcast that you have registered receivers for is on this list, then it will still function as it did previously. However, if the broadcast that you have registered to receive is not on this list then you should use some alternative solution like:
Create the receiver at runtime by calling Context.registerReceiver(),
instead of declaring the receiver in the manifest.
Use a scheduled job to check for the condition that would have
triggered the implicit broadcast.
For more information
It's not supported in Oreo as manifest tag, you must have to register it at an Service/ Activity with context.registerReceiver(). Or you use the WorkManager to schedule something for specific network conditions.
I want to know the difference between services and broadcast receivers, can anyone point out an example that can be observed on android mobile devices.
Thanks
Service: If you want to do something in background , this will be running always in background even if the application closed. You can create this in separate process and also you can give your service to other app if you want. Downloading any content or Music is good example
Broadcast Reciever: Usually system will send some info which can be recieved by your app if you would wish to ,by registering. And you can do something what you want when that thing happens by using onReceive method.
Example is the system will send BroadcastReceiver when new sms arrives or Booting done
Here is good article : Service and BroadcastReceiver
Service is used when you want to do something in background, any long running process can be done using Service in Background. For example, you want to play music when your application gets close. In that case service will be running in background with music.
Example of Service
BroadcastReceiver is used when you want to fire some stuff or code during some event. For example, event can be on Boot of Device. If you want to perform something when device Boots, date and time changed etc...
Example of BroadcastReceiver
I think of it possibly a different way. A Service receives intents that were sent specifically to your application, just like an Activity. A Broadcast Receiver receives intents that were broadcast system-wide to all apps installed on the device.
(The reason I say a Service is a bit like an Activity is that: You wouldn't broadcast a message saying "start Activity MyActivity" across all apps installed on the device. It is only for your specific app.)
Of course, as others mentioned, a Service can continue running in the background, whereas a Broadcast Receiver should finish quickly (e.g. if it is running for more than 5 seconds it may be killed by the OS). The Broadcast Receiver can still run in the background (when app is closed) under certain circumstances. For this, it's worth mentioning that there are actually two types of Broadcast Receivers - Manifest-declared, and Context-registered. They have different lifespans and restrictions - the former can receive broadcasts in the background with certain restrictions, while the latter cannot receive broadcasts in the background (app must be running and active) but has no restrictions on the types of intents that can be received.
Both services and broadcast receivers must be specifically invoked (via an intent), but for services this is usually a specific call (e.g. when your app is started or when the user clicks some button) whereas for broadcast receivers they don't need to be explicitly started as they will start anyway when a relevant broadcast is made.
Here's how I would think of it:
Type
Displays UI?
Can continue running for a long time when app is closed?
Can receive intents when app is closed?
Intents must specifically target your app?
Restricted list of intents that can be specified?
Activity
Yes
No
Yes
Yes
No
Service
No
Yes
Yes
Yes
No
Manifest-declared Broadcast Receiver
No
No
Yes
No
Yes1
Context-registered Broadcast Receiver
No
No
No
No
No
1: Only if you target Android 8.0 or above. The restrictions are not applied if the intent specifically targets your app. The restricted list of intents can be found here.
I have written android app which kills background processes. My app looks for running processes lets say if browser opens it will close and kill it. Now it will check again this after some delay.
The thing annoying me is that I have to refresh it again and again, I need to catch any app launched on phone or something else and see whether lets say 'is a browser' then close and kill it.
Any efficient method to solve this problem ??
You can use a broadcast receiver, this sits and waits for the system to send it a prompt. Standard actions at the moment are:
Standard Broadcast Actions
These are the current standard actions that Intent defines for receiving broadcasts (usually through registerReceiver(BroadcastReceiver, IntentFilter) or a tag in a manifest).
ACTION_TIME_TICK
ACTION_TIME_CHANGED
ACTION_TIMEZONE_CHANGED
ACTION_BOOT_COMPLETED
ACTION_PACKAGE_ADDED
ACTION_PACKAGE_CHANGED
ACTION_PACKAGE_REMOVED
ACTION_PACKAGE_RESTARTED
ACTION_PACKAGE_DATA_CLEARED
ACTION_UID_REMOVED
ACTION_BATTERY_CHANGED
ACTION_POWER_CONNECTED
ACTION_POWER_DISCONNECTED
ACTION_SHUTDOWN
There is also:
ACTION_PACKAGE_FIRST_LAUNCH
but I think this is only sent to the Package that start's the app. (and is API 12)
So yeah instead of polling us a Listener.
Take a look at ACTION_PACKAGE_RESTARTED
Broadcast Action: The user has restarted a package, and all of its processes have been killed. All runtime state associated with it (processes, alarms, notifications, etc) should be removed.
Example Implementation
Perhaps you can use this?
Another function may be useful to you, getRecentTasks.
What is a BroadcastReceiver? What are its uses and how can I use it?
Start by reading the documentation. Also, copying from Application Fundamentals:
Broadcast receivers
A broadcast receiver is a component that responds to system-wide
broadcast announcements. Many
broadcasts originate from the
system—for example, a broadcast
announcing that the screen has turned
off, the battery is low, or a picture
was captured. Applications can also
initiate broadcasts—for example, to
let other applications know that some
data has been downloaded to the device
and is available for them to use.
Although broadcast receivers don't
display a user interface, they may
create a status bar notification to
alert the user when a broadcast event
occurs. More commonly, though, a
broadcast receiver is just a "gateway"
to other components and is intended to
do a very minimal amount of work. For
instance, it might initiate a service
to perform some work based on the
event.
A broadcast receiver is implemented as a subclass of
BroadcastReceiver and each broadcast
is delivered as an Intent object. For
more information, see the
BroadcastReceiver class.
Finally, read in Common Tasks how you can utilize BroadcastReceivers to listen for messages and set alarms.
A broadcast is generated by android on occurrence of some action , BroadcastReceiver class enables the developer to handle the situation on occurence of the event/action . Action can be arrival of msg or call , download complete , boot completed , etc.
Broadcast Receivers simply respond to broadcast messages from other applications or from the system itself. These messages are sometime called events or intents. For example, applications can also initiate broadcasts to let other applications know that some data has been downloaded to the device and is available for them to use, so this is broadcast receiver who will intercept this communication and will initiate appropriate action.
I like this slide, because it focuses on Broadcast Receiver and offers simple description. The minor problem is that the updated date was a little bit old ( in 2011 ).
Link
Android Application Component: BroadcastReceiver Tutorial
(retrieved from the slide)
Broadcast Receiver
Receives and Reacts to broadcast Intents
No UI but can start an Activity
Extends the BroadcastReceiver Base Class
BroadCastReciever is an Android Component that helps you to know handle registered System Events or Application Events.
For Example:
System Events Such us : the screen has turned off, the battery is low, or a picture was captured.
Applications can also initiate broadcasts—for example, to let other applications know that some data has been downloaded to the device and is available for them to use... etc
In simple terms
A broadcast receiver is basically an interface that you can implement so that your app can subscribe to system changes like when the system has finished booting, or a charger is connected/disconnected or airplane mode is switched on/off etc.
Can anybody tell what is the use of a BroadcastReceiver and give an example in Android?
Can someone give a time zone change example using a BroadcastReceiver?
I think the android developers documentation explains it pretty good:
A broadcast receiver is a component that does nothing but receive and react to broadcast announcements. Many broadcasts originate in system code — for example, announcements that the timezone has changed, that the battery is low, that a picture has been taken, or that the user changed a language preference. Applications can also initiate broadcasts — for example, to let other applications know that some data has been downloaded to the device and is available for them to use.
(see developer.android.com)
On your android system broadcasts are used as an instrument of notifications. As the name suggests, they are broadcastet through your whole system. With a broadcast receiver you can catch these broadcast notifications.
Think about the broadcast receiver as a normal listener. If you listening for free beer and someone yells "free beer here", than you will react on that :) Thats your real life broadcast receiver example :D
A broadcast receiver is a component which allows us to register for system or application events. All registered receivers for an event will be notified by Android once this event happens.
Android system periodically broadcast messages about things that are happening, such as the battery status changed, the Wi-Fi came on, or the phone’s orientation changed. You can pick up these state changes and perform actions after intercepting them and all this is done using broadcast receivers. Broadcast receivers receive and react to broadcasts generated by system or apps .