Problem with Gear tutorial: "Attempt to index global "background" <a nil value>

Getting Started Newbie Questions
#1

Hi guys

I am learning Corona. I learn from Corona tutorial video. I was in Gear Animation #6. The tutorial is about to make my pictures fitting on the Android’s screen (which is bigger)

this is the link to the video
http://www.youtube.com/watch?v=MYIAHR1CbBs

everything was correct until I typed these four code lines

background.xScale = display.contentWidth / background.contentWidth
background.yScale = display.contentHeight / background.contentHeight
background.x = centerX
background.y = centerY

The purpose is to make the background fits on the screen. But my result was not the same as the tutorial. The background became bigger but it was hidden at the left top of the screen. I can see only part of it.

this is the mistake reported

<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers error> …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: attempt to p
erform arithmetic on global ‘rotateAmount’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:40: in function
<…ers>Copyright © 2009-2010 A n s c a , I n c .
Version: 2.0.0
Build: 2011.484
Runtime error
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:16: attempt to i
ndex global ‘background’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:16: in main chun
k
Runtime error: …ers\Public\Documents\CoronaPratice2\lesson8\main.lua:16: attem
pt to index global ‘background’ (a nil value)
stack traceback:
[C]: ?
…ers\Public\Documents\CoronaPratice2\lesson8\main.lua:16: in main chun
k

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Anyone can help me?
[import]uid: 54857 topic_id: 10308 reply_id: 310308[/import] </…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers></…ers>

#2

Wow - you’ve posted a lot of errors.

OK, so let’s take a look…

All your errors until close to the end relate to rotateAmount being a nil value. Is it a nil value? Have you defined it?

If you comment out any code relating to the background, are you error free?

Let me know :slight_smile:

Peach [import]uid: 52491 topic_id: 10308 reply_id: 37759[/import]

#3

with looking at ur errors i can tell that u are using enterFrame or timer which is calling repeatedly or any recursive function

ahhh i am so smart

ok now my guess

case 1 if you are getting this error from starting then may be spelling mistake with ur object and hence the object is no there

case 2 in between you are removing the object and thats why u are getting errors
more case soon
[import]uid: 12482 topic_id: 10308 reply_id: 37782[/import]