How do I move an existing display object behind another in Corona Lua?

Question

If I have two existing display objects in Corona, lets say do1 and do2. Assume do1 is drawn first then do2, so do2 will be on top.

Is there a way to say "put do2 behind do1" in corona Lua? If yes can you give me an example?

Answer 1

If do1 and do2 are in a display group they appear in the order you insert them as:

local group = display.newGroup()
group:insert(do1)
group:insert(do2)

Groups are also numerically indexed and the objects are in display order based on the index:

assert(group[1] == do1) -- do1 is on the bottom
assert(group[2] == do2) -- do2 is on the top (front)

If you happen to add your items out of order, you can move another item to the top in a number of ways:

local group = display.newGroup()
group:insert(do2) -- do2 is on the bottom
group:insert(do1) -- do1 is on the top (front)

-- Move do2 to front by re-inserting it - only one instance will exist in group
group:insert(do2)

assert(group[1] == do1) -- do1 is on the bottom
assert(group[2] == do2) -- do2 is on the top (front)

-- Move do2 to the front

do2:toFront()

assert(group[1] == do1) -- do1 is on the bottom
assert(group[2] == do2) -- do2 is on the top (front)

-- Move do2 to the back

do2:toBack()

assert(group[1] == do2) -- do2 is on the bottom
assert(group[2] == do1) -- do1 is on the top (front)

See also toFront() and toBack().

You an only put items in the front or back. As far as I know there's no way to arbitrarily place items. You can however maintain display order in another list and insert them based on that order.

Answer 2

Just Googled this question and since it's still unanswered, here's the way to do it for others in need:

local group = display.newGroup()
group:insert(do1)

for n = 1, group.numChildren do
    if group[n] == do1 then
        group:insert(n, do2) -- this puts do2 behind do1
        break
    end
end