Processing.instances returns null

Question

I have a webpage running 2 processing sketches, i want to call Processing.instances[0].exit() as suggested in this question: Dynamically "unload" a Processing JS sketch from canvas

But when i call Processing.instances it returns null, and i get no errors on the javascript console - also Processing.instances.length returns (0).

Here the javascript code:

document.onkeydown = function(e) { // or document.onkeypress
e = e || window.event;
if (e.keyCode == 115 || e.keyCode == 83) { //press "s" or "S"
    alert(Processing.instances.length);
}
};

And here the url for the website: http://culturadigital.cc/nuevaweb

Thanks

Also here: `var canvases = getElementsByClassName(document, 'processingsketch'); if(canvases){ for(j=0;j — fartagaintuxedo, Aug 29 '13 at 19:28

score 1 · Accepted Answer · edited May 23 '17 at 12:21

1

As you figured out from the pjs forum, Processing.instances is in uncertain fate. How about this:

document.onkeydown = function(e) { // or document.onkeypress
  e = e || window.event;
  if (e.keyCode == 115 || e.keyCode == 83) { //press "s" or "S"
    var canvases = document.getElementsByClassName("processingsketch");
            window.alert(canvases.length);
    if (canvases) {
      var ps = Array();
      for (j=0;j<canvases.length;j++) {
        ps[j]=Processing.getInstanceById(canvases[j].getAttribute('id'));
      }
      for (j=0;j<canvases.length;j++) {
        window.alert("ps " + ps[j]);
        window.alert(canvases[j].getAttribute('id'));
        if(ps[j]){ps[j].exit();} //per fartagaintuxedo's comment below: to avoid second error because once it exits then there is no longer an instance in that canvas
        canvases[j].width = canvases[j].width; //to obliterate the canvas instead of just freezing it
      }
    }
  }
};

For reference, there might be better ways to clear the canvas here: How to clear the canvas for redrawing

edited May 23 '17 at 12:21

Community

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answered Aug 29 '13 at 22:36

Petros Koutsolampros

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apparently `exit` should make the sketch not visible.. what happens here is that it freezes.. strange.. then the second time i press "s" i get the same error again – fartagaintuxedo Aug 29 '13 at 22:53
but i guess thats just what it has to do.. just freeze, why not. – fartagaintuxedo Aug 29 '13 at 22:59
just a note, to avoid second error *because once it exits then there is no longer an instance in that canvas* just add `if(ps[j]){ps[j].exit();}` – fartagaintuxedo Aug 29 '13 at 23:09
You probably then just have to play with js/html and the canvas. For example you can add `canvases[j].width = canvases[j].width;` after ps[j].exit(); – Petros Koutsolampros Aug 29 '13 at 23:09
yep, great! that will do : ) – fartagaintuxedo Aug 29 '13 at 23:10

score 1 · Answer 2 · answered Aug 30 '13 at 01:06

If anyone else finds this question: don't use Processing.instances - we never wrote it to be accessible. There is a Processing.getInstanceById() function that you pass in your canvas id, and get back the sketch that's running on it.

Get your instance with .getInstanceById(), then call .exit() on that.

Processing.instances returns null

2 Answers2