I’ve develop android application, and one question.
As you know, When we use LiveActivity, we must specify @id/android:list for ListView ID.
But, When I use @+id/android:list instead of @id/android:list, it is working fine.
What is different between @+id/android:list and @id/android:list ??
The fundamental difference between
@+ is that
@+ is signaling that you need to add a new id, the
@ by itself tells the compiler to look for an existing id.
As you know, When we use LiveActivity,
we must specify @id/android:list for
But, When I use @+id/android:list
instead of @id/android:list, it is
No, those will give you compile errors. Colons are not valid characters in Java field names, and so those IDs are illegal.
Switching back to legal Android syntax, if you are declaring your own ID (no
android: in the value), the first time you use the ID in a file, you are supposed to have the
+ sign. The second and subsequent times, the
+ sign is not needed, though it seems to cause no harm if you have in there as well.
It seems that there are two ways to reference to the platform id
@id/android:list. The ListActivity documentation shows both (the first one in text, second in the example) but does not clarify if there’s any difference.
@+id/android:list as the ListView’s id seems to work too. I assume that what happens here is that a copy of the
android.R.id.list identifier is added to the application’s own ID list.
In my opinion
@android:id/list is the clearest way for referencing to
Resource IDs in Android are specific to a package (which is good, or else you’d have lots of conflicts if your app is dealing with several packages at the same time).
@+id/list will create a resource ID in your
app (=your package) with the name
"list" and give it a unique ID. In code, that would be
@android:id/list will use the ID
"list" from the package android (which, in code, would be