Assuming you are using the url sidebar property to load your sidebar's HTML (i.e. a hosted web page), you can use the extension's Run in Iframe feature to communicate between the iframe extension and the parent window's extension.
To achieve this, first enable the extension to run in iframes (Settings > Run in Iframes) and then you can use the extension.js to load your sidebar and handle messaging. For example, the following code loads a page that has a button with identification btnSave:
Hosted web page file:
<html>
<head>
</head>
<body>
<div id="mySidebar">
My sidebar form
<br />
<button id="btnSave">Save</button>
</div>
</body>
</html>
extension.js file:
appAPI.ready(function($) {
// Check if running in iframe and the sidebar page loaded
if (appAPI.dom.isIframe() && $('#mySidebar').length) {
// Set click handler for button to send message to parent window
$('#btnSave').click(function() {
appAPI.message.toCurrentTabWindow({
type:'save',
data:'My save data'
});
});
// End of Iframe code ... exit
return;
}
// Parent window message listener
appAPI.message.addListener(function(msg) {
if (msg.type === 'save') {
console.log('Extn:: Parent received data: ' +
appAPI.JSON.stringify(msg.data));
}
});
// Create the sidebar
var sidebar = new appAPI.sidebar({
position:'right',
url: 'http://yourdomain.com/sidebar_page.html',
title:{
content:'Sidebar Title',
close:true
},
opacity:1.0,
width:'300px',
height:'650px',
preloader:true,
sticky:true,
slide:150,
openAction:['click', 'mouseover'],
closeAction:'click',
theme:'default',
scrollbars:false,
openOnInstall:true,
events:{
onShow:function () {
console.log("Extn:: Show sidebar event triggered");
},
onHide:function () {
console.log("Extn:: Hide sidebar event triggered");
}
}
});
});
However, if you are using the html sidebar property to load your sidebar's HTML, then this solution will not work since the extension does not run in this context. However, you may be able to utilize the methods described in the StackOverflow thread you quoted to communicate with the parent window (this would be browser specific) that in turn can communicate with the extension using our CrossriderAPI event.
[Disclaimer: I am a Crossrider employee]