Error of the Font of the Cited URL in Bibliography Using Bib$\rm \LaTeX{}$ in APA Style

This midnight, I tried to compile my $\rm \LaTeX$ document with a so-called "bibliography", which contains a URL. The link should be in typewriter font after using the command \urlstyle{tt} under adding the url package to the preamble. I googled for almost 2 hours, but the blog posts suggested that using this method should work. I even tried to copy some minimum working examples from the web to test if they work. They really worked and so I'm puzzled. Ten minutes ago, I just find out what's going wrong: the url package should never go before the several lines in the preamble that are responsible for adding an APA-style bibliography.
The \ll command in Vim-$\rm \LaTeX$ seems not doing well with Biber. Whenever the aux file exists, \ll won't execute biber, causing the resulting pdf file to have no change in the bibliography.
Hope I can use less time to figure out any mistake next time.

This Weekend's Work on Vim

1. Installed some useful Vim plugins, such as Vundle (Vim plugins management tool), NERDTree (file browser), Easymotion, Loremipsum (random text generator), Vim-surround (surround text with brackets), Vim-snipmate (for autogenerated code), Vim-addon-mw-utils, Tlib_vim (dependency for Vim-snipmate), FuzzyFinder (quick finding tool for files, etc) and L9 (dependency for FuzzyFinder).
2. Do some custom insert mode keyboard mapping. (automatical completion of brackets)