Get Selected Folder at runtime

I'm trying to write a plugin that will pass back the currently selected folder for processing. When I try using something like:

var folder = api.getSelectedFolder();
if ( folder )
   alert( folder.getUrl() );

I get undefined. I'm putting it in the uiReady function of AddPlugin. What I need to be able to do is to put the folder in the function call of an HTML button click event. Something like:

<input type="button" id="mybutton" onclick="javascript:parent.myfunction($currentFolder)">

So that when it's clicked it sends the selected fold to the "myfunction".

Any help is greatly appreciated.