Check for listener

Solar2D General Questions/Discussion
#1

Is it possible to test whether an object is listening for an event? For example, if a group passed into a function is listening for tap events.

#2

Well, if  you set up your listeners like this:

local function onTap( self, event ) end local myGroup = display.newGroup() for i = 1, 10 do local obj = display.newCircle( myGroup, 10 \* i, 10 \* i, 5 ) -- randomly add tap listener to objects. if( math.random(1,2) == 1) then obj.tap = onTap obj:addEventListener( "tap" ) end end

Then, you can simply check for the presence of ‘tap’ on the object and assume that means it is listening.

-- Check for tap listeners and remove for i = 1, myGroup.numChildren do if( myGroup[i].tap ) then print( i, " was listening for tap. Removing...") myGroup[i]:removeEventListener( "tap" ) myGroup[i].tap = nil end end

By the end of the sample code above, you’ve detected the objects that are listening and removed/cleared them so they won’t be seen as listening if checked again later.

#3

Additionally, I think you can dig into objects like this:
 

  1. Checking if obj is using a ‘touch’ table listener:

    if( obj._tableListeners[“touch”] ) then print( “listening for ‘touch’” ) end

  2. Checking if obj is using a ‘touch’ runtime (function) listener:

    if( obj._functionListeners[“touch”] ) then print( “listening for ‘touch’” ) end

I’m sure the tables exist (_functionListeners and _tableListeners), but I’m not 100% sure about the structure of the contents of those tables.

You may want to dump them.  If you have SSK2, you can do this:

table.print\_r( obj.\_functionListeners )  table.print\_r( obj.\_tableListeners) 

or this if print_r crashes:

-- SSK2 2017.010 or later table.xinspect( obj.\_functionListeners ) table.xinspect( obj.\_tableListeners)
#4

I’d like to know if the addEventListener function has been called to attach a particular event, rather than particular event handler, onto an object. The problem being that the handler function does not need to be called, in this case, ‘tap’. I could override addEventListener, but doing that involves overriding all the display.newXxx functions to add the modified function to every display object.

#5

I think I answered that in my second post.

Tip: When I post responses, I usually go through a few edits and even additional posts.  So, if you see that I just answered, give me a few more minutes to clean it up and re-format, plus add any other things that occur to me.

Sorry for the delay in my response-style, but that’s just the way I think.

#6

Nice one. That hadn’t appeared when I posted. Post clash!

#7

Well, if  you set up your listeners like this:

local function onTap( self, event ) end local myGroup = display.newGroup() for i = 1, 10 do local obj = display.newCircle( myGroup, 10 \* i, 10 \* i, 5 ) -- randomly add tap listener to objects. if( math.random(1,2) == 1) then obj.tap = onTap obj:addEventListener( "tap" ) end end

Then, you can simply check for the presence of ‘tap’ on the object and assume that means it is listening.

-- Check for tap listeners and remove for i = 1, myGroup.numChildren do if( myGroup[i].tap ) then print( i, " was listening for tap. Removing...") myGroup[i]:removeEventListener( "tap" ) myGroup[i].tap = nil end end

By the end of the sample code above, you’ve detected the objects that are listening and removed/cleared them so they won’t be seen as listening if checked again later.

#8

Additionally, I think you can dig into objects like this:
 

  1. Checking if obj is using a ‘touch’ table listener:

    if( obj._tableListeners[“touch”] ) then print( “listening for ‘touch’” ) end

  2. Checking if obj is using a ‘touch’ runtime (function) listener:

    if( obj._functionListeners[“touch”] ) then print( “listening for ‘touch’” ) end

I’m sure the tables exist (_functionListeners and _tableListeners), but I’m not 100% sure about the structure of the contents of those tables.

You may want to dump them.  If you have SSK2, you can do this:

table.print\_r( obj.\_functionListeners )  table.print\_r( obj.\_tableListeners) 

or this if print_r crashes:

-- SSK2 2017.010 or later table.xinspect( obj.\_functionListeners ) table.xinspect( obj.\_tableListeners)
#9

I’d like to know if the addEventListener function has been called to attach a particular event, rather than particular event handler, onto an object. The problem being that the handler function does not need to be called, in this case, ‘tap’. I could override addEventListener, but doing that involves overriding all the display.newXxx functions to add the modified function to every display object.

#10

I think I answered that in my second post.

Tip: When I post responses, I usually go through a few edits and even additional posts.  So, if you see that I just answered, give me a few more minutes to clean it up and re-format, plus add any other things that occur to me.

Sorry for the delay in my response-style, but that’s just the way I think.

#11

Nice one. That hadn’t appeared when I posted. Post clash!