Difference between Activity Context and Application Context

Question

This has me stumped  I was using this in Android 2 1-r8 SDK   ProgressDialog show getApplicationContext             and also in   Toast t   Toast makeText getApplicationContext            using getApplicationContext   crashes both ProgressDialog and Toast      which lead me to this question   What is the actual differences between a activity context and application context  despite sharing the wording  Context

User · Answer

You can see a difference between the two contexts when you launch your app directly from the home screen vs when your app is launched from another app via share intent.

Here a practical example of what "non-standard back stack behaviors", mentioned by @CommonSenseCode, means:

Suppose that you have two apps that communicate with each other, App1 and App2.

Launch App2:MainActivity from launcher. Then from MainActivity launch App2:SecondaryActivity. There, either using activity context or application context, both activities live in the same task and this is ok (given that you use all standard launch modes and intent flags). You can go back to MainActivity with a back press and in the recent apps you have only one task.

Suppose now that you are in App1 and launch App2:MainActivity with a share intent (ACTION_SEND or ACTION_SEND_MULTIPLE). Then from there try to launch App2:SecondaryActivity (always with all standard launch modes and intent flags). What happens is:

if you launch App2:SecondaryActivity with application context on Android < 10 you cannot launch all the activities in the same task. I have tried with android 7 and 8 and the SecondaryActivity is always launched in a new task (I guess is because App2:SecondaryActivity is launched with the App2 application context but you're coming from App1 and you didn't launch the App2 application directly. Maybe under the hood android recognize that and use FLAG_ACTIVITY_NEW_TASK). This can be good or bad depending on your needs, for my application was bad.
On Android 10 the app crashes with the message
"Calling startActivity() from outside of an Activity context requires the FLAG_ACTIVITY_NEW_TASK flag. Is this really what you want?".
So to make it work on Android 10 you have to use FALG_ACTIVITY_NEW_TASK and you cannot run all activities in the same task.
As you can see the behavior is different between android versions, weird.
if you launch App2:SecondaryActivity with activity context all goes well and you can run all the activities in the same task resulting in a linear backstack navigation.

I hope I have added some useful information

User · Answer

I think when everything need a screen to show   button  dialog layout     we have to use context activity  and everything doesn t need a screen to show or process   toast  service telelphone contact     we could use a application context

User · Answer

I found this table super useful for deciding when to use different types of Contexts      An application CAN start an Activity from here  but it requires that a new task be created   This may fit specific use cases  but can create non-standard back stack behaviors in your application and is generally not recommended or considered good practice  This is legal  but inflation will be done with the default theme for the system on which you are running  not what   s defined in your application  Allowed if the receiver is null  which is used for obtaining the current value of a sticky broadcast  on Android 4 2 and above    Original article here

User · Answer

The reason I think is that ProgressDialog is attached to the activity that props up the ProgressDialog as the dialog cannot remain after the activity gets destroyed so it needs to be passed this ActivityContext  that also gets destroyed with the activity whereas the ApplicationContext remains even after the activity gets destroyed

User · Answer

They are both instances of Context  but the application instance is tied to the lifecycle of the application  while the Activity instance is tied to the lifecycle of an Activity  Thus  they have access to different information about the application environment   If you read the docs at getApplicationContext it notes that you should only use this if you need a context whose lifecycle is separate from the current context  This doesn t apply in either of your examples   The Activity context presumably has some information about the current activity that is necessary to complete those calls   If you show the exact error message  might be able to point to what exactly it needs     But in general  use the activity context unless you have a good reason not to

User · Answer

This obviously is deficiency of the API design  In the first place  Activity Context and Application context are totally different objects  so the method parameters where context is used should use ApplicationContext or Activity directly  instead of using parent class Context   In the second place  the doc should specify which context to use or not explicitly

User · Answer

Use getApplicationContext   if you need something tied to a Context that itself will have global scope   If you use Activity  then the new Activity instance will have a reference  which has an implicit reference to the old Activity  and the old Activity cannot be garbage collected

[android] Difference between Activity Context and Application Context

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