Haskell fetchName from X11 library does not return the name of the window

Question

Having the following Haskell code:

import           Control.Concurrent
import           Data.Time.Clock
import           Debug.Trace
import           Graphics.X11
import           Graphics.X11.Xlib.Extras

main :: IO ()
main = do
  d <- openDisplay ""
  loop d

loop :: Display -> IO ()
loop d = do
  time <- getCurrentTime
  (w, _) <- getInputFocus d
  maybeName <- fetchName d w
  windowAttrs <- getWindowAttributes d w
  print $ show time ++ " Name: " ++ show maybeName ++ " Width: " ++ show (wa_width windowAttrs)
  threadDelay 1000000
  loop d

The window title returned by fetchName is always Nothing.

Haskell X11 library is a wrapper around Xlib

Possibly related issues:

• The width of the window is either correct or it has the value 1.
• XFetchName always returns 0

Answer 1

It looks like fetchName isn't always filled in. Instead you need to use the _NET_WM_NAME property:

import           Control.Concurrent
import           Data.Time.Clock
import           Debug.Trace
import           Graphics.X11
import           Graphics.X11.Xlib.Extras

main :: IO ()
main = do
  d <- openDisplay ""
  loop d

loop :: Display -> IO ()
loop d = do
  time <- getCurrentTime
  (w, _) <- getInputFocus d
  a <- internAtom d "_NET_WM_NAME" False
  p <- getTextProperty d w a
  ps <- wcTextPropertyToTextList d p
  windowAttrs <- getWindowAttributes d w
  print $ show time ++ " Name: " ++ show ps ++ " Width: " ++ show (wa_width windowAttrs)
  threadDelay 1000000
  loop d

This is what XMonad does:

https://github.com/xmonad/xmonad/blob/8b055621e92e7ade127043e968f50713c15a00a0/src/XMonad/ManageHook.hs#L71-L80