How do I redraw airline after setting window-local variable

Question

:help airline states that variables related to sections can be window-local. The example from help shows how to do it for a plugin:

  function! MyPlugin(...)
    if &filetype == 'MyPluginFileType'
      let w:airline_section_a = 'MyPlugin'
      let w:airline_section_b = '%f'
      let w:airline_section_c = '%{MyPlugin#function()}'
      let g:airline_variable_referenced_in_statusline = 'foo'
    endif
  endfunction
  call airline#add_statusline_func('MyPlugin')

I want to know how can I do it from the window itself, or understand a proper way to configure autocmd for this purpose. After executing :let w:airline_section_b = 'foo', the bar isn't updated. Is there a way to redraw it with new changes? I found :AirlineRefresh, but it just resets everything to defaults.

Answer 1

A simple way to do this would be to just run the function definition and airline function add for each window—that is, to do it from the window itself should require no modification other than removing the filetype check and changing plugin functions for your functions.

You could use an autocommand on the WinEnter event (I may have that wrong—someone feel free to edit and correct me): it could declare some kind of function or variable referenced in a global function to be used.

---

It occurs to me that some of the confusion is in the way the example references plugins.

A .vimrc file contains Vimscript, the special scripting language builtin to vim. It is, for all intents and purposes, an extension of the Ex commands—:global, :join, etc., are all valid Vimscript commands. And so are :function and :autocmd.

To summarize, you can just place things like

function MyFunc()
  echo 'do something here'
endfunction

directly in your vimrc.

(This ability to put Vimscript code in files is not unique to 3rd-party plugins or the plugin directory of the 'runtimepath'.)