Question

I’ve read through much of the Android documentation and I’ve yet to find any statement that says what an id value prefix of “@+id” means. I know what “@string” and variations of that mean, but not the variation with the “+”. Besides giving me the answer, can you show me where in the Android docs this is documented?

Answer 1

The plus sign simply indicates that the ID should be created if it doesn’t exist.

It’s common practice to use @+id/foo when defining a new View in a layout, and then use @id/foo to reference the View from another part of the layout (say, in a RelativeLayout hierarchy) or R.id.foo to reference it from code.

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UPDATE: Docs are here: Declaring Layout – Attributes – ID