I need to add a slider bar to adjust the transparence of layers like those in old 2.1 Map Layer widget. But the 2.3 LayerList Widget does not provide a function like that? Do I have to write codes myself? Thanks!
Robert Scheitlin's TOC (table of contents) widget does that, plus a bunch of other cool stuff. It's on the code gallery and you can get it either compiled (no coding required) or uncompiled (to let you make code changes if you wish).
