Using listeners and signals with Nasal: Difference between revisions

Using listeners and signals with Nasal (view source)

10 bytes added , 27 January 2021

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 <tt>setlistener()</tt> returns a unique listener id on success, and <tt>nil</tt> on error. The id is nothing else than a counter that is 0 for the first Nasal listener, 1 for the second etc. You need this id number to remove the listener. Most listeners are never removed, so that one doesn't assign the return value, but simply drop it.
-Listener callback functions can access up to four values via regular function arguments, the first two of which are property nodes in the form of a <tt>props.Node()</tt> object hash. The third is a indication of the operation: 0 for changing the value, -1 for removing a child node, and +1 for adding a child. The fourth indicates whether the event occurred on the node that was listened to and is always 0 if the previous argument is not 0.
+'''Listener callback functions''' can access up to four values via regular function arguments.
+The first two of which are property nodes in the form of a <tt>props.Node()</tt> object hash.
+The third is a indication of the operation: 0 for changing the value, -1 for removing a child node, and +1 for adding a child.
+The fourth indicates whether the event occurred on the node that was listened to and is always 0 if the previous argument is not 0.
 Here is the syntax supposing you have set a callback function named ''myCallbackFunc'' via <tt>setlistener</tt> (''setlistener(myNode, myCallbackFunc)''):