function 'for - do - end" / moving object ( Corona Sdk ) - function

Question

I'm beginner for coding, I've questions :
First I'd like know why that code is not moving :
local speed = 5
function cube ()
for i = 1,20,2 do
local rect = display.newRect(50,50,50,50)
rect.x = screenleft-300 + (50*i)
rect.y = _y
rect.x = rect.x - speed
if (rect.x < -450 )then
rect.x = 1200
end
end
end
timer.performWithDelay(1, cube, -1)
Secondly : What's the difference between
Runtime:addEventListener( "enterFrame", cube )
and
timer.performWithDelay(1, cube, -1)
Because I get the same result with both of them
And to be done, Why when I use the function "for" to duplicate something like the square i've done upside, this one put the image behind eachother and not like the square beside eachother ( the image i'm trying to duplicate has more than 4 side )
Thanks for all your reply !
thks a lot dude , I know what you mean by here but my question is little bit weird maybe lol and maybe we can't do it
I try to explain again :
for i=1,10,1 do
local Circle = display.newCircle(50, 20, 20)
Circle.x = _x + (50*i)
Circle.y = _y
end
So here I've a Circle line like that 00000 (imagine 0 are circle ^^)
and I want to make that line moving from the left to the right screen, but when i try to make it move with :
Circle.x = Circle.x - speed
Corona don't recognize the " circle.x " so I can't, maybe because is insert into the"FOR"
SO my question is : "How to move this Circle line if that's possible with the "FOR" ?
I hope I've Been clearer
Anyway, Thanks for all

Answer 1

I'll answer your second question first:
Runtime:addEventListener( "enterFrame", cube )
The function addEventListener adds a listener to the object’s list of listeners. When the named event occurs (in this case "enterFrame"), the listener will be invoked and be supplied with a table representing the event. In your code, the listener will call cube() on every frame (normaly, games run at 60 frames per second).
timer.performWithDelay(delay, listener [, iterations])
performWithDelay does what it says it does: Call a specified function after a delay. The timer function returns an object that can be used with other timer.* functions. In your code timer.performWithDelay(1, cube, -1) the function is calling cube() every 1ms and it is going to do so forever. This is not a good thing to do. There's nothing catching the return of the timer function and it is going to be running forever.
Now, to answer your main question. I believe what you are trying to do is create a square an move it in the screen. If that's correct, here's how you should do it:
local square = display.newRect(100,100,50,50)
local speed = 2
-- called every frame
local function moveSquare()
square.x = square.x + speed
end
Runtime:addEventListener("enterFrame", moveSquare)
The reason your code doesn't do what you want it to do is because you misunderstood a some basic CoronaSDK things.
Hope this little code helps you to understand more about how CoronaSDK works. Don't forget to check the documentation of Corona in http://docs.coronalabs.com/

Answer 2

You're creating an object locally in a loop and trying to move it outside of the loop. This doesn't work due to the way lua uses local variables. See http://www.lua.org/pil/4.2.html for more info about this.
Also, you'll need to place the objects into a single display group in order to move them easily. If you're using Box2D physics at all, I recommend reading up on it more at http://docs.coronalabs.com/api/library/physics/index.html.
Your code:
for i=1,10,1 do
local Circle = display.newCircle(50, 20, 20)
Circle.x = _x + (50*i)
Circle.y = _y
end
Should Be Changed to:
local Circle = display.newGroup(); --Forward declaration of Variable. Place this before any calls for it.
local speed = 2;
for i=1,10,1 do
local object = display.newCircle(50,20,20);
object.x = _x + (50*i);
object.y = _y;
Circle:insert(object); --Insert this local object into the display group
end
function moveCircle()
Circle.x = Circle.x + speed;
end
Runtime:addEventListener( "enterFrame", moveCircle);
This will move the Circle line every frame, on the X-axis, by the speed variable's value.
If you're trying to move it with a for-loop, then we'd need to see more of you code in context.