What is @ in "@+id/idname" format mean in android?

Question

They say:

The at sign (@) is required when you're referring to any resource object from XML. It is followed by the resource type (id in this case), a slash, then the resource name (edit_message).

I'm not quite understand what @ mean, who can give a more specific explanation?

@PareshMayani I dont think this is a duplicate both questions have different context — SMR, Feb 19 '15 at 06:33
Thank you. at original it is a little duplicate on description but I reedit later. @SMR — Peter Zhu, Feb 19 '15 at 06:36
It was a duplicate question earlier but now updated details has made it more clear and unique! — Paresh Mayani, Feb 19 '15 at 06:39

TheLostMind · Accepted Answer · 2015-02-19T06:28:56.827

3

If the ID is not already created, then + will create it. You will need it only the first time you refer to that id.

From docs :

The plus sign (+) before the resource type is needed only when you're defining a resource ID for the first time. When you compile the app, the SDK tools use the ID name to create a new resource ID in your project's gen/R.java file that refers to the EditText element. With the resource ID declared once this way, other references to the ID do not need the plus sign.

Like the docs say, the @ symbol means you are referring to an xml resource. For example : @string/edit_message means you are trying to refer to a string with the id edit_message defined in an xml file.

edited Feb 19 '15 at 06:28

answered Feb 19 '15 at 06:21

TheLostMind

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um, then, what is the `@` mean? – Peter Zhu Feb 19 '15 at 06:23
so the `@+id/idname` mean I create a resource which id is "idname" and `@` means I refer to the resource id name after I just create it? – Peter Zhu Feb 19 '15 at 06:31
Actually, - *you try to refer to the resource using "@" and create it (thats why you have the "+") if it is not already present* – TheLostMind Feb 19 '15 at 06:34
I get it, I have accept your answer and you can add your last comment into your answer, to make it clear. – Peter Zhu Feb 19 '15 at 06:38

score 2 · Answer 2 · answered Feb 19 '15 at 07:13

@ sign means you are referring to a resource under res folder.

@drawable

refer to a .png or button state images.

@anim

refer to animation

@id/anyID

refer to any pre Created id

@+id/createNewID

+ create a new id and name it createNewID and

+sign only works with id. you cannot use it with anim,drawable.

Note

You can not create any Resource programatically other than id.

SMR · Answer 3 · 2015-02-19T07:45:44.733

In each android project there is a gen folder inside src where R.java is created automatically and all the IDs of resources used/created in XMLs belong here.

As the docs say:

The at sign (@) is required when you're referring to any resource object from XML.

This means that you are going to refer an ID from R.java if you add + then the corresponding id will be created if it does not exists in R.java already. As the docs say:

The plus sign (+) before the resource type is needed only when you're defining a resource ID for the first time. When you compile the app, the SDK tools use the ID name to create a new resource ID in your project's gen/R.java file that refers to the EditText element. With the resource ID declared once this way, other references to the ID do not need the plus sign.

So + sign is required only when you want to create a new id for the view. If it is already created in the same file then it will simply reuse that id instead of creating a new id with the same name.

NOTE: you can use + with IDs only.

@ has so many uses. The one which are used mostly are:

@id/ to reference from R.id
@string/ references R.string similarly...
@drawable/ -> R.drawable
@array/ -> R.array
@color/ -> R.color

Finally you can use @android to refer resources defined in the android SDK.

score 1 · Answer 4 · answered Feb 19 '15 at 09:08

@ is used to give identity or to refer to the existing resource in XML File.

'@' specifies what kind of resource you are about to access. if you use @id, it will refer to any resources in layout of project. if you use @string, it will locate to a string that you may usually specify in Strings.XML

there are so many other resources like : @drawable, @color, @style, @array, @dimen, @layout & @xml..

you can use according to your requirement.

What is @ in "@+id/idname" format mean in android?

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