New to android need to understand "?android:attr/actionBarSize"

Question

I was going through Lars Vogel's tutorial on using Fragments and I came across the following code:

android:layout_marginTop="?android:attr/actionBarSize"

I am not sure what ?android:attr means, especially the question mark.

Phantômaxx · Accepted Answer · 2014-06-10T07:59:16.853

53

android:attr

is an attribute.

In specific,

android:layout_marginTop="?android:attr/actionBarSize"

means: "the size (height) of the action bar".
? is a special character that means it's an Android internal feature.

edited Jun 10 '14 at 07:59

answered Dec 25 '13 at 13:34

Phantômaxx

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answer includes some mystery. More detail needed. – oiyio Mar 21 '19 at 15:16
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@oiyio **?android** indicates a *system* feature. Not a customized/customizable one. Mystery solved. – Phantômaxx Mar 21 '19 at 15:20

score 12 · Answer 2 · edited Mar 17 '21 at 09:08

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Instead of write Numerical number in value of android:layout_marginTop , you can use the height specified by actionBarSize like an Example in Android Training .

You can use ?android:attr or ?attr [ in case support library ] If you need to use any android attributes[ attr ] can be found in R.attr

For More Description about ?android:attr Question 1 ,Question 2

edited Mar 17 '21 at 09:08

Vadim Kotov

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answered May 11 '14 at 18:16

ahmed hamdy

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Is there a built in 2 x ?attr/actionBarSize? – Martin Erlic Nov 21 '16 at 18:07
@santafebound Do you mean multiple action bar size value?? – ahmed hamdy Nov 22 '16 at 11:15
@ahmedhamdy Yes – Martin Erlic Nov 22 '16 at 11:59
I think there isn't built in for multiple action bar size value or setting it as `2x actionBarSize`. I think you need to setting numerical value into `values.xml` file. – ahmed hamdy Nov 22 '16 at 12:42

score 2 · Answer 3 · edited Dec 25 '13 at 15:18

2

While building android apps, one requires to know the properties of the Android client. Such as screen size etc. One such method is by using android:attr which is android attributes. Here you have mentioned to return a specific attribute by mentioning the keyword after / symbol. Here the keyword is actionBarSize.

The ? symbol is an operator which is used to access system configurations and properties in Android

edited Dec 25 '13 at 15:18

Veger

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answered Dec 25 '13 at 13:50

Aniruddha Sarkar

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Where can you get a list of all of those configurations and properties, using the same method? – android developer Mar 31 '14 at 09:19

New to android need to understand "?android:attr/actionBarSize"

3 Answers3

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