Question

I am wondering what’s the difference between @+id/android:list and @+id/list. I know the last one which is a regular id assignment but the first looks different. What makes it special?

Where I saw it:
I was studying on ListView, ListAdapter and things like that and the author define the ListView in layout xml file as below :

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:orientation="vertical"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   >
<ListView
    android:id="@+id/android:list"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    />
<TextView
    android:id="@+id/android:empty"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:text="@string/main_no_items"/>
</LinearLayout>

and also let me mention @+id/android:empty id as well.

And he also extends ListActivity class.

Here is the source of the article.

And also what’s in my mind as questions are :

1. Should we extend ListActivity? Maybe I want an Activity which also contains other Views.
2. We use @+id/android:list just because we extend ListActivity or we can use the same convention if we extend Activity?

Thanks.

Answer 1

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 R.id.list.

@android:id/list will use the ID “list” from the package android (which, in code, would be android.R.id.list.

EDIT: Need to add the corrections David Hedlund pointed out: The proper reference would be @android:id/list. Also, + indicates you’re defining a new ID – you obviously don’t need that when you’re referencing something that was defined in the Android API.