Clarification on the docs for PendingIntent.FLAG_CANCEL_CURRENT

Question

From the documentation of Pending Intent FLAG_CANCEL_CURRENT in Android:

by canceling the previous pending intent, this ensures that only entities given the new data will be able to launch it. If this assurance is not an issue, consider FLAG_UPDATE_CURRENT

Can anyone explain what this line means?

Answer 1

Once you create a new PendingIntent with FLAG_CANCEL_CURRENT, anything holding a previous PendingIntent for the same Intent will no longer be able to execute that original PendingIntent.

For example, suppose we have this:

Intent i=new Intent(this, Foo.class);

i.putExtra("key", 1);

PendingIntent pi=PendingIntent.getActivity(this, 0, i, 0);

and we use that PendingIntent with, say, a Notification.

Later on, we execute:

Intent i=new Intent(this, Foo.class);

i.putExtra("key", 2);

PendingIntent pi2=PendingIntent.getActivity(this, 0, i, PendingIntent.FLAG_CANCEL_CURRENT);

At this point, the PendingIntent created originally (pi) is no longer valid, and whatever we use pi2 for will see the updated extra value (2).

If, instead, we did:

Intent i=new Intent(this, Foo.class);

i.putExtra("key", 2);

PendingIntent pi2=PendingIntent.getActivity(this, 0, i, PendingIntent.FLAG_UPDATE_CURRENT);

At this point, pi and pi2 both represent the same PendingIntent, and both will see the updated extra value (2).

Or, if we did:

Intent i=new Intent(this, Foo.class);

i.putExtra("key", 2);

PendingIntent pi2=PendingIntent.getActivity(this, 0, i, 0);

At this point, pi and pi2 still represent the same PendingIntent, but the extras are unchanged, as getActivity() returns the original PendingIntent without applying the new extras.

Most times, FLAG_UPDATE_CURRENT is a fine answer when you are trying to replace extras inside a PendingIntent.