Error: attempt to call method (a nil value)

Solar2D General Questions/Discussion
#1

Hi,

I have an “enterframe” listener to constantly set the speed of a falling display object. On collision this display object is destroyed. When the object is destroyed my call to “setLinearVelocity” returns nil and I get an error dispite having checks to see if the object exists before I call “setLinearVelocity”. Below is my code:

function setspeed(e)  
 if (bangflag == false) then  
 if (b ~= nil) then  
 vx, vy = b:getLinearVelocity()   
 b:setLinearVelocity( vx, 110 + (level \* 10) )  
 end  
 end  
end  
  
Runtime:addEventListener("enterFrame", setspeed);

“bangflag” is a flag I set whenever a collision is detected so this should not fire during a collision. “b” is a var used to hold display objects and I check to make sure it is not nil before calling “setLinearVelocity”. Please note removing the event listener is not an option as I need it for other display objects. [import]uid: 31694 topic_id: 24155 reply_id: 324155[/import]

#2

What is the error?

You say it occurs on the setLinearVelocity line.

Now, that is AFTER the getLinearVelocity line, so that suggests that B is OK

In the line
b:setLinearVelocity( vx, 110 + (level * 10) )

you also use variables vx , and level

Assuming vx worked because no error on the line above, what is the value of level at that point?
ps, you can also test for b like this

if b then
…

[import]uid: 108660 topic_id: 24155 reply_id: 97471[/import]

#3

Sorry “getLinearVelocity” doesn’t work either. I had it commented out.

if b then doesn’t seem to make any difference. [import]uid: 31694 topic_id: 24155 reply_id: 97483[/import]

#4

OK.
b is not nil.
But maybe it isn’t what you expect it to be.

if it was an Apple, you would not expect it to be able to Eat()
>> “b” is a var used to hold display objects <<

Objects plural?
Are they all physics bodies?
Is b an array or table?

try this:

local bb = event.target  
  
 if (bangflag == false) then  
  
 vx, vy = bb:getLinearVelocity()   
 bb:setLinearVelocity( vx, 110 + (level \* 10) )  
  
 end

[import]uid: 108660 topic_id: 24155 reply_id: 97485[/import]

#5

Here is how my spawn function works:

function spawn()  
 b = bean.newBean(oldColour);  
 function b:collision(e)  
 --Code here to remove display objects that collide  
 end  
 b:addEventListener("collision", b);  
 beans[#beans + 1] = b;  
end

I would like to set the speed of only the last bean created. I tried “beans[#beans]:setLinearVelocity( vx, 110 + (level * 10) )” but then when a the last spawned bean is removed I had it altering the speed of beans I wasn’t intending to alter. [import]uid: 31694 topic_id: 24155 reply_id: 97491[/import]

#6

This seems to have worked:

if (b and b == beans[#beans]) then [import]uid: 31694 topic_id: 24155 reply_id: 97510[/import]

#7

I’d like to see the remove code.

If you do something like:

bean:removeSelf()

and do not do:

bean = nil

Then bean still exists as a table just with the display object removed which removes all of the :functions with it. You have to set it to nil to make sure the table reference is gone too.
[import]uid: 19626 topic_id: 24155 reply_id: 97524[/import]