Why does my relative layout occupy full screen width

Question

Why does my relative layout occupy full screen width

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="#f00"
    >
    <Button  
        android:id="@+id/Button01"  
        android:text="Press Here"  
        android:layout_alignParentRight="true" 
        android:layout_width="wrap_content"   
        android:layout_height="wrap_content"></Button> 
     <Button  
        android:id="@+id/Button02"  
        android:text="02"  
        android:layout_alignParentLeft="true" 
        android:layout_width="wrap_content"   
        android:layout_height="wrap_content"></Button>  
</RelativeLayout>

I have specified the relative layout to "wrap_content", then why does it occupy full screen space. Out put is same even if i say android:layout_width="fill_parent".

Enlighten me please!

EDIT : I think i was not very clear with my question earlier. Apologies for that. When I have 2 child views in a relative layout and one of them is left aligned to parent and other is right aligned and relative layouts width is WRAP_CONTENT then I expected the layouts width to be just the sum of width of 2 buttons (isn't that's what WRAP_CONTENT means??). I know there are other ways of achieving the UI im looking for but Im just trying to understand these relative layout tags properly.

EDIT 2: I have experimented a bit and it looks like if we using Layout_AlighParentRight with its parent's width as WRAP_CONTENT then the upper layout width is used for calculation (like few answers pointed out below). But we are using just the Layout_alignParentLeft then it works as expected and layout width is not extending to the complete screen. Thanks for the help folks!

Solution 1

cause you have a

        android:layout_alignParentLeft="true" 

width an object , and a

        android:layout_alignParentRight="true" 

width another object , then the layout extends to both side , giving you the full width layout.

But when you use Layout_alignParentXXXXX , and you put in parent WRAP_CONTENT , that makes children to go to the upper layout with a width defined.

Solution 2

This line makes the "Press Here" button (Button01) align to the right:

android:layout_alignParentRight="true" 

That makes your layout fill the parent in width.

Comments

[Santosh]

Thanks for the answer, but its not very clear to me. Are you saying that if we use Layout_alignParentXXXX and the parents width is WRAP_CONTENT, then upper layout (parent's parent) width is used for calculation?? is that true?

[A.Quiroga]

my experience told me that , but you can try it , putting another upper LinearLayout with a width for example of 50dip and see the result :)

[Santosh]

I have experimented a bit and it looks like if we using Layout_AlighParentRight with its parent's width as WRAP_CONTENT then the upper layout width is used for calculation (like you pointed out). But we are using just the Layout_alignParentLeft then it works as expected and layout width is not extending to the complete screen. Thanks for the help Quiroga!