Defining Z order of views of RelativeLayout in Android

In Android starting from API level 21, items in the layout file get their Z order both from how they are ordered within the file, as described in correct answer, and from their elevation, a higher elevation value means the item gets a higher Z order.

This can sometimes cause problems, especially with buttons that often appear on top of items that according to the order of the XML should be below them in Z order. To fix this just set the android:elevation of the the items in your layout XML to match the Z order you want to achieve.

I you set an elevation of an element in the layout it will start to cast a shadow. If you don't want this effect you can remove the shadow with code like so:

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
   myView.setOutlineProvider(null);
}

I haven't found any way to remove the shadow of a elevated view through the layout xml.

The easiest way is simply to pay attention to the order in which the Views are added to your XML file. Lower down in the file means higher up in the Z-axis.

Edit: This is documented here and here on the Android developer site. (Thanks @flightplanner)

If you want to do this in code you can do

View.bringToFront();

see docs

Please note, buttons and other elements in API 21 and greater have a high elevation, and therefore ignore the xml order of elements regardless of parent layout. Took me a while to figure that one out.