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!

Answer 1

The other answers have correctly pointed out that when your relative layout’s width is set to wrap_content, and its children are aligned to both left and right, the relative layout takes the width of its parent – in this case, the entire screen. If, however, both children were aligned to one side, the relative layout would be as wide as the widest child.

Now if you want the two buttons to be placed next to each other, and the relative layout to be as wide as the sum of the widths of the buttons, a slightly different approach is needed. Instead of positioning both buttons relative to the parent, do that with one button only (e.g, the first one). Let’s say its positioning is left unchanged (android:layout_alignParentRight="true"). Now the button is floated to the right, so the second button, in order to be position next to it, has to be aligned to the first button’s left side. Thus, we just add android:layout_toLeftOf="@id/Button01" (and remove the android:layout_alignParentLeft="true" part).

For more, I suggest you check out a very friendly tutorial on relative layouts.