Attached file indicator checkbox

Hello,

I have been trying to script a checkbox to get checked whenever a file is attached to the PDF, whether by using buttons that perform the function, or if the user uses the paper clip icon in the left-side toolbar.  This is my checkbox:

The script in my checkbox is in the layout:ready event:

if (event.target.dataObjects) {  this.rawValue = "1";
}
else {  this.rawValue = "0";
}

The problem is, the script doesn't fire until I make a selection on a drop-down somewhere else in the form.  What am I missing?

I have scripts in the Attach Files and Remove Files buttons that check/uncheck the box, but that doesn't help any if the user uses the toolbar.

Any help would be greatly appreciated.