what does the "@+android:id/title" mean?

Question

In normal, we should use @+id/ to define an id and use @id to reference an id. Today I found @+android:id/title in apps/settings/res/layout/preferenc_progress.xml.

How to understand it and how to use it?

Answer 1

It is used for resources that are shipped with the SDK.

You can take a look at them by browsing to

[PATH TO ANDROID SDK]/platforms/android-[VERSION]/data/res

By using the android in android.R.whatever you just specify the R file to look up. For more information you should read Accessing Platform Resources.

Answer 2

That belongs to the app preferences activity screen definition. title and summary are standard Android fields of a TextView preference item.