Expecting a table? - lua

Question

I started learning Corona yesterday so sorry for my ignorance. Can someone please explain why it is "expecting table" on line 108 (physics.addBody( newBalloon, "dynamic", { radius=70, bounce=0.8 } )). All I want it to do is take the image from the object sheet and display it.
local composer = require( "composer" )
local scene = composer.newScene()
local physics = require( "physics" )
physics.start()
-- Configure image sheet
local sheetOptions =
{
frames =
{
{
x = 0,
y = 0,
width = 112,
height = 142
},
{
x = 0,
y = 142,
width = 112,
height = 284
},
{
x = 0,
y = 284,
width = 112,
height = 568
},
{
x = 0,
y = 568,
width = 112,
height = 710
},
{
x = 0,
y = 710,
width = 112,
height = 852
},
{
x = 0,
y = 852,
width = 112,
height = 994
},
{
x = 0,
y = 994,
width = 112,
height = 1136
},
{
x = 0,
y = 1136,
width = 112,
height = 1278
},
{
x = 0,
y = 1278,
width = 112,
height = 1420
},
},
}
local objectSheet = graphics.newImageSheet( "gameObjects.png", sheetOptions )
local tapCount = 0
local platform
local balloon
local balloon2
local balloon3
local tapText
local function createBalloon()
newBalloon = display.newImageRect( mainGroup, objectSheet, 1, 112, 142 )
physics.addBody( newBalloon, "dynamic", { radius=70, bounce=0.8 } )
newBalloon.myName = "Bigballoon"
local whereFrom = math.random( 3 )
if ( whereFrom == 1 ) then
-- From the left
newBalloon.x = 30
newBalloon.y = math.random( display.contentHeight )
elseif ( whereFrom == 2 ) then
-- From the top
newBalloon.x = 60
newBalloon.y = math.random( display.contentHeight )
elseif ( whereFrom == 3 ) then
-- From the right
newBalloon.x = 90
newBalloon.y = math.random( display.contentHeight )
end
end
local function pushBalloon()
-- balloon:applyLinearImpulse( 0.2, -2, balloon.x, balloon.y )
-- tapCount = tapCount + 1
-- tapText.text = tapCount
balloon.gravityScale = 10
balloon:applyLinearImpulse( 0.1, 0, balloon.x, balloon.y )
end
local function pushBalloon2()
-- balloon:applyLinearImpulse( 0.2, -2, balloon.x, balloon.y )
-- tapCount = tapCount + 1
-- tapText.text = tapCount
balloon2.gravityScale = 10
balloon2:applyLinearImpulse( 0.1, 0, balloon2.x, balloon2.y )
end
local function pushBalloon3()
-- balloon:applyLinearImpulse( 0.2, -2, balloon.x, balloon.y )
-- tapCount = tapCount + 1
-- tapText.text = tapCount
balloon3.gravityScale = 10
balloon3:applyLinearImpulse( -0.1, 0, balloon3.x, balloon3.y )
end
-- -----------------------------------------------------------------------------------
-- Scene event functions
-- -----------------------------------------------------------------------------------
-- create()
function scene:create( event )
local sceneGroup = self.view
-- Code here runs when the scene is first created but has not yet appeared on screen
physics.pause()
local background = display.newImageRect( "background.png", 360, 570 )
background.x = display.contentCenterX
background.y = display.contentCenterY
local platform = display.newImageRect( "platform.png", 300, 50 )
platform.x = display.contentCenterX
platform.y = display.contentHeight-25
balloon = display.newImageRect( "balloon.png", 112, 112 )
balloon.x = display.contentCenterX
balloon.y = display.contentCenterY
balloon.alpha = 0.8
balloon2 = display.newImageRect( "balloon.png", 112, 112 )
balloon2.x = display.contentCenterX-100
balloon2.y = display.contentCenterY
balloon2.alpha = 0.8
balloon3 = display.newImageRect( "balloon.png", 112, 112 )
balloon3.x = display.contentCenterX+100
balloon3.y = display.contentCenterY
balloon3.alpha = 0.8
createBalloon()
tapText = display.newText( tapCount, display.contentCenterX, 20, native.systemFont, 40 )
tapText:setFillColor( 0, 0, 0 )
physics.addBody( platform, "static" )
physics.addBody( balloon, "dynamic", { radius=50, bounce=0.6 } )
physics.addBody( balloon2, "dynamic", { radius=50, bounce=0.6 } )
physics.addBody( balloon3, "dynamic", { radius=50, bounce=0.6 } )
balloon:addEventListener( "tap", pushBalloon )
balloon.gravityScale = 0
balloon:setLinearVelocity( 0, -10 )
balloon2:addEventListener( "tap", pushBalloon2 )
balloon2.gravityScale = 0
balloon2:setLinearVelocity( 0, -10 )
balloon3:addEventListener( "tap", pushBalloon3 )
balloon3.gravityScale = 0
balloon3:setLinearVelocity( 0, -10 )
end
-- show()
function scene:show( event )
local sceneGroup = self.view
local phase = event.phase
if ( phase == "will" ) then
-- Code here runs when the scene is still off screen (but is about to come on screen)
elseif ( phase == "did" ) then
-- Code here runs when the scene is entirely on screen
physics.start()
end
end
-- hide()
function scene:hide( event )
local sceneGroup = self.view
local phase = event.phase
if ( phase == "will" ) then
-- Code here runs when the scene is on screen (but is about to go off screen)
elseif ( phase == "did" ) then
-- Code here runs immediately after the scene goes entirely off screen
physics.pause()
end
end
-- destroy()
function scene:destroy( event )
local sceneGroup = self.view
-- Code here runs prior to the removal of scene's view
end
-- -----------------------------------------------------------------------------------
-- Scene event function listeners
-- -----------------------------------------------------------------------------------
scene:addEventListener( "create", scene )
scene:addEventListener( "show", scene )
scene:addEventListener( "hide", scene )
scene:addEventListener( "destroy", scene )
-- -----------------------------------------------------------------------------------
return scene

Answer 1

You should declare newBalloon as local when you initialize it in createBalloon(). Also, mainGroup == nil when you pass it as the parent group to display.newImageRect(). For these reasons, newBalloon is probably nil when you pass it to physics.addBody() instead of being a DisplayObject, which is what that method requires as its first argument.
For safety, in createBalloon(), you could do this:
local newBalloon = display.newImageRect( ... )
if newBalloon then
physics.addBody( newBalloon, ... )
else
print("WARNING: newBalloon is nil in createBalloon")
end
By the way, if you want all the balloons to be in the same GroupObject, you could add this:
local balloonGroup -- forward declaration
...
local function createBalloon()
local newBalloon = display.newImageRect( balloonGroup, ... )
...
end
local scene:create()
...
balloonGroup = display.newGroup()
sceneGroup:insert( balloonGroup )
balloonGroup:toFront()
...
balloonGroup:insert( balloon )
balloonGroup:insert( balloon2 )
...
end