<merge/> in custom View xml layout

Merge useful for LinearLayout and FrameLayout its not suitable for RelativeLayout.

Obviously, using works in this case because the parent of an activity's content view is always a FrameLayout. You could not apply this trick if your layout was using a LinearLayout as its root tag for instance. The can be useful in other situations though.

check this:

For anyone that might still be struggling with this, you should specify the parentTag attribute inside the merge tag. You will also need to specify layout_height and layout_width to make it work.

    <merge
        tools:parentTag="android.widget.RelativeLayout"
        tools:layout_width="match_parent"
        tools:layout_height="match_parent"
    >
    // Child Views
    </merge>

The editor should display everything properly now.