How to fix a bug in Corona SDK?

Question

Corona SDK

When I added an event listener to the green circle (boostButton) Corona started throwing an error.

Here is the code:

local score = 0
local boost = 1

display.setDefault( "background", 10/225, 10/225, 10/225)
display.setStatusBar(display.HiddenStatusBar)

local circle = display.newCircle(display.contentCenterX, display.contentCenterY, 50 )

local scoreText = display.newText(score, display.contentCenterX, 90, native.systemFont, 24)

local boostButton = display.newCircle(display.contentCenterX, 400, 30 ):setFillColor(40/225, 60/225, 30/225)--зелёный бустер


local function pushCircle()
  score = score + 1*boost
  scoreText.text = score
end
circle:addEventListener("tap", pushCircle);

local function scoreBoost()
  boost = boost + 1
end
boostButton:addEventListener('tap', scoreBoost)

Answer 1

Remove setFillColor, make it a separate line. It turns out that you are assigning to the boostButton variable not a button object, but the result of the setFillColor function, which is nil, which is what the error tells you about.

Answer 2

local boostButton = display.newCircle(display.contentCenterX, 400, 30 )
local test = boostButton:setFillColor(40/225, 60/225, 30/225)

In this case, boostButton now contains the result of newCircle, i.e. button link.
But the test variable contains the result of the setFillColor operation, i.e. nil