How is +id valid inside a RelativeLayout?

Question

In a relative layout I see a pattern as:

<TextView 
    android:id=“@+id/txt_id”
    etc
   android:layout_alignBottom="@+id/some_other_txt”
    etc
/>

<TextView
 android:id="@+id/some_other_txt"

 etc
/>

I thought +id is used only when creating an id for a widget. Is this a kind of “trick” to layout a widget relative to another widget declared later in the file?

UPDATE:
This question is specifically about the RelativeLayout possitioning. Not about the difference in syntax in general as the linked question

You reference a View **anticipately** (a View which hasn't yet been created in the xml) by using `@+id`. But I prefer creating the View **before** and then refer it by using `@id`. — Phantômaxx, Mar 30 '15 at 15:17
@DiegoFreniche:I think there is no duplicate. My question is about RelativeLayout and not in general the difference between the syntax — Jim, Mar 30 '15 at 15:18
@DerGolem:Is this somewhere documented? I could not find it somewhere — Jim, Mar 30 '15 at 15:19
Oh, now you are asking too much... I can't remember where did I get this bit of info. Maybe, from a book. — Phantômaxx, Mar 30 '15 at 15:22
In RelativeLayout the order in which you write your widgets it's not the same as they appear on screen. Android Lint needs to check all relationships too, so maybe this is a way to avoid Lint from giving you warnings — Diego Freniche, Mar 30 '15 at 15:24
@DerGolem:I am asking in the sense I could not even google about this trick — Jim, Mar 30 '15 at 15:24
This pdf is in French, but you can always use Google Translate... http://cedric.cnam.fr/~farinone/SETMO/seance2PourSETMO.pdf - Search `@+id > @id` — Phantômaxx, Mar 30 '15 at 15:26

score 0 · Answer 1 · answered Mar 30 '15 at 15:24

0

Its just a reference point for placing the different elements in the layout builder.

answered Mar 30 '15 at 15:24

RifatRashid

45
6

score 0 · Answer 2 · edited May 23 '17 at 12:06

0

From this SO answer

The first time you reference an ID, use the @+ prefix, which tells the resource builder to add the ID,

Here you're making a forward reference to a widget & id that's not already defined:

<TextView 
    android:id=“@+id/txt_id”
    etc
   android:layout_alignBottom="@+id/some_other_txt”
    etc
/>

Here you are defining it:

<TextView
 android:id="@+id/some_other_txt"

More context here

edited May 23 '17 at 12:06

Community

1
1

answered Mar 30 '15 at 15:25

Diego Freniche

5,225
3
32
45

But shouldn't be this declared to the widget that has the id assigned? – Jim Mar 30 '15 at 15:26
And that would be considered the first time you reference it. ;) – Martin Marconcini Mar 30 '15 at 15:29
Being an **anticipated reference**, the id is created **before** the Widget has it **explicitly assigned**. – Phantômaxx Mar 30 '15 at 15:30

How is +id valid inside a RelativeLayout?

2 Answers2