What is the purpose of Android's <merge> tag in XML layouts?

Question

I've read Romain Guy's post on the <merge /> tag, but I still don't understand how it's useful. Is it a sort-of replacement of the <Frame /> tag, or is it used like so:

<merge xmlns:android="...."> <LinearLayout ...>     .     .     . </LinearLayout> </merge> 

then <include /> the code in another file?

Answer 1

<merge/> is useful because it can get rid of unneeded ViewGroups, i.e. layouts that are simply used to wrap other views and serve no purpose themselves.

For example, if you were to <include/> a layout from another file without using merge, the two files might look something like this:

layout1.xml:

<FrameLayout>    <include layout="@layout/layout2"/> </FrameLayout> 

layout2.xml:

<FrameLayout>    <TextView />    <TextView /> </FrameLayout> 

which is functionally equivalent to this single layout:

<FrameLayout>    <FrameLayout>       <TextView />       <TextView />    </FrameLayout> </FrameLayout> 

That FrameLayout in layout2.xml may not be useful. <merge/> helps get rid of it. Here's what it looks like using merge (layout1.xml doesn't change):

layout2.xml:

<merge>    <TextView />    <TextView /> </merge> 

This is functionally equivalent to this layout:

<FrameLayout>    <TextView />    <TextView /> </FrameLayout> 

but since you are using <include/> you can reuse the layout elsewhere. It doesn't have to be used to replace only FrameLayouts - you can use it to replace any layout that isn't adding something useful to the way your view looks/behaves.