As of Mendix 4 I don't think this option is configurable. I think you'll need some custom javascript event to grab the Mendix toasters and add a fade out event to them.
See this dojo documentation: http://dojotoolkit.org/reference-guide/1.7/dojo/fadeOut.html
Paul
I don't think you can close those messages automatically. One idea: you could show a popup web form instead and put a microflow timer on that web form that calls a close form microflow after a certain amount of time has elapsed.
Mike
So, I have "a" solution that should be cross-browser supported. Some of the other pieces I saw either drained performance or were not supported across browsers like IE. Let me preface this by saying I'm in no way a good js developer. But if you want to test this out, it worked for me:
(function() {
//Set time to check
var checkInterval = 3000,
lastNumOfToasters = 0;
setInterval(function () {
var toasters = dojo.query('.mendixToaster_message');
if (lastNumOfToasters == toasters.length)
for (var i = 0; i < toasters.length; i++)
toasters[i].click();
lastNumOfToasters = toasters.length;
}, checkInterval);
})();
Save this text as AddMxToasterFade.js in the 'theme' directory of your project. Then load it in your index3.html page with a basic script tag right below mxui.js.
<script type="text/javascript" src="AddMxToasterFade.js"></script>
I have not done a lot of testing - again, this was a 5 minute solution, but feedback would be great.