App crashes on device whenever I remove a snapshot

[evanspro]

My app crashes everytime it tries to remove a snapshot. It happens on the device (android), but not while running on Simulator.

-- Invalidates snapshot at every frame
local function invalidateSnapshot()
	snapshot.invalidate()
end

-- Called when removing the snapshot
function removeSnapshot()
	
	-- Stopping the update of the snapshot
	Runtime:removeEventListener("enterFrame", invalidateSnapshot)
	
	-- Removing the snapshot
	if snapshot ~= nil then
		if snapshot.group ~= nil then
			snapshot.group:removeSelf()
			snapshot.group = nil
		end
		snapshot:removeSelf()
		snapshot = nil
	end

end

Here’s the error:
WARNING: script.lua:18: the ‘group’ property of snapshot objects is read-only

snapshot:removeSelf() seems to be the reason it crashes. There’s a function that invalidates that snapshot onEnterFrame, but I do stop it right before removing the snapshot.

Weird thing is that I can’t find a single thing on google about “snasphot boject being read-only”.

[Kan98]

This is referring to Group in snapshot

Solar2D Documentation — API Reference | type | SnapshotObject | group

[evanspro]

Wow, I can’t believe I missed this documentation page

But then, what would be the proper way to remove/clear a snapshot? Should I move the content of snapshot.group to something else and simply then set snapshot = nil?

So far, I’ve removed this part:

if snapshot.group ~= nil then
	snapshot.group:removeSelf()
	snapshot.group = nil
end

Unfortunately, the app still crashes and goes instantly back to the launcher but this time, without returning any error on the Corona Console.

EDIT: It seems to work now and doesn’t crash (don’t know since I haven’t updated anything, but well…). My question still remaines: what’s the propert way to remove/clear a snapshot?

[Kan98]

I always do this with both canvas and snapshots.

local snap = display.newSnapshot(display.actualContentWidth, display.actualContentHeight);

snap.x = display.contentCenterX

snap.y = display.contentCenterY

snap.clearColor = {0, 1, 0}

local rects = {}

for i = 1, 10, 1 do

    local rect = display.newRect(math.random(-100, 100), math.random(-100, 100), math.random(10, 32), math.random(10, 32))

    rect:setFillColor(math.random(), math.random(), math.random(), 1);

   

    rects[i] = rect

    snap.group:insert(rect)

end

timer.performWithDelay(200, function ()

    local idx = #rects

    local rect=  rects[idx]

    display.remove(rect)

    rect = nil

    table.remove(rects, idx)

    snap:invalidate()

    print(snap.group.numChildren)

   

    if snap.group.numChildren <= 0 then

        snap:removeSelf()

        snap = nil

    end

    print(tostring(snap))

end, 10);

Put all children into tables, and remove them if snapshots need to be deleted.

    for i = #rects, 1, -1 do
        local rect = rects[i]
        if rect then
            rect:removeSelf()
            table.remove(rects, i)
        end
    end

    snap:removeSelf()
    snap = nil

    rects = nil

[evanspro]

Thank you a lot for your replies, helps a lot!

Just one more question about your way: do you really need to remove every rectangle inserted into snap.group as the group should behave like a normal group? As far as I know, removing a group also remove every other item inserted into it (… please, tell me it does or I’m gonna have a very bad week lol).

[Kan98]

Yeah, snap group will remove all children together.
My way is to make sure in case you need to change the drawn child objects.