Function + Event + Parameter

Solar2D Lua Language
1

Hello,

I have a question regarding passing a parameter to a function from an event listener.

Not sure that it sounds very clear. Basically, in the example below, when i press the magenta (myButton) rectangle, i want to move the grey rectangle (myRectangle) from a Y distance passed from the listener :

local myRectangle = display.newRect(150, 300, 150, 50)  
myRectangle.strokeWidth = 3  
myRectangle:setFillColor(140, 140, 140)  
myRectangle:setStrokeColor(180, 180, 180)  
local myButton = display.newRect(100, 400, 150, 50)  
myButton.strokeWidth = 3  
myButton:setFillColor(140, 0, 55)  
myButton:setStrokeColor(180, 180, 180)  
local function moveY (distance)  
  
 myRectangle.y = myRectangle.y - distance  
  
end  
  
myButton:addEventListener("touch", moveY(20))

i tried also:

myButton:addEventListener("touch", moveY(event, 20))  
myButton:addEventListener("touch", moveY(,20))

Nothing seems to work.

Any idea if it is possible or if there is a workaround?

Thanks for the help!

Dim [import]uid: 100310 topic_id: 24852 reply_id: 324852[/import]

2

You should pass parameter like this
[lua]myButton:addEventListener(“touch”, function() moveY(event, 20) end)[/lua]

or

[lua]local closure = function() moveY(event, 20) end
myButton:addEventListener(“touch”, closure)[/lua]
[import]uid: 64174 topic_id: 24852 reply_id: 100801[/import]

3

YOU ROCK!

Thanks a lot,
Dim [import]uid: 100310 topic_id: 24852 reply_id: 100808[/import]

4

One problem leads to another =)

when i now try to use the phase of the event, i run into an error (showed below).

local myRectangle = display.newRect(150, 300, 150, 50)  
myRectangle.strokeWidth = 3  
myRectangle:setFillColor(140, 140, 140)  
myRectangle:setStrokeColor(180, 180, 180)  
local myButton = display.newRect(100, 400, 150, 50)  
myButton.strokeWidth = 3  
myButton:setFillColor(140, 0, 55)  
myButton:setStrokeColor(180, 180, 180)  
local function moveY (event, distance)  
  
 if event.phase == "ended" then -- I get here an 'attempt to index local 'event' (a nil value)  
 myRectangle.y = myRectangle.y - distance  
 end  
  
  
end  
  
local closure = function() moveY(event, 20) end  
myButton:addEventListener("touch", closure)

Any idea?

Thanks,
Dim
[import]uid: 100310 topic_id: 24852 reply_id: 100811[/import]

5

Is that the only way you want to do it? Here’s another example:

[code]
local myRectangle = display.newRect(150, 300, 150, 50)
myRectangle.strokeWidth = 3
myRectangle:setFillColor(140, 140, 140)
myRectangle:setStrokeColor(180, 180, 180)

local myButton = display.newRect(100, 400, 150, 50)
myButton.strokeWidth = 3
myButton:setFillColor(140, 0, 55)
myButton:setStrokeColor(180, 180, 180)

distance = 20

local function moveY( event )
if event.phase == “ended” then
myRectangle.y = myRectangle.y - distance
end
end
myButton:addEventListener( “touch”, moveY )
[/code] [import]uid: 77199 topic_id: 24852 reply_id: 100820[/import]

6

Hey,

Thanks for jumping in.

Well, in this example, yes. But now consider a graphic keyboard of 4 letters (ABCD).

To show what the user is writing, each of these images representing a letter, when pressed, will add their string (“A”, “B”, etc.) to the existing word.

So they will all need an eventListener each calling for a specific function (for example, addAToTheWord, addBToTheWord, etc).

fine with me.

But now, consider that the keyboard is not only 4 letters, but 1000. In that case, you would like to create a generic ‘addToTheWord’ function that takes the character as parameter.
No?

Using the ‘closure’ solution is fine. But if you also want to use the event parameter (for phases for example), then you can’t pass both (event + the character/index as a parameter)

Maybe i am completely wrong in the approach, i’m pretty new to coding.
How would you do that? [import]uid: 100310 topic_id: 24852 reply_id: 101123[/import]