Hot reload on save

Question

I'm currently using a terminal and vim on OSX as a development environment for Flutter. Things are going pretty well except that the app does not reload when I save any dart files. Is there a way to trigger that behavior?Currently I have to go to the terminal and hit "r" to see my changes.

Solution 1

Sorry for the plug, but I wrote a very simple plugin to handle this.

It makes use of Flutter's --pid-file command line flag to send it a SIGUSR1 signal.

You can achieve the same result as my two-line plugin by adding this to an autocmd

silent execute '!kill -SIGUSR1 "$(cat /tmp/flutter.pid)"'

And launching Flutter with the --pid-file flag.

Solution 2

I made a vim plugin hankchiutw/flutter-reload.vim based on killing with SIGUSR1.

You don't have to use --pid-file flag with this plugin. (Thanks to the pgrep :))

Simply execute flutter run, modify your *.dart file and see the reloading.

Solution 3

I did it with the excellent little tool called entr. On OS/X you can install it from brew: brew install entr. The home page of the tool is at http://eradman.com/entrproject/

Then you start flutter run with the pidfile as @nobody_nowhere suggests.

How do you run entr depends on the level of service. In the simplest case you just do find lib/ -name '*.dart' | entr -p kill -USR1 $(cat /tmp/flutter.pid)

But such invocation will not detect new files in the source tree (because find builds a list of files to watch only once, at the start). You can get away with slightly more complex one-liner:

while true
do
    find lib/ -name '*.dart' | \
        entr -d -p kill -USR1 $(cat /tmp/flutter.pid)
done

The -d option makes entr exit when it does detect a new file in one of the directories and the loop runs again.

I personally use even more complex approach. I use Redux and change to middleware or other state files does not work with hot reload, it doesn't pick up these changes. So you need to resort to hot restart. I have a script hotrestarter.sh:

#!/bin/bash

set -euo pipefail
PIDFILE="/tmp/flutter.pid"

if [[ "${1-}" != "" && -e $PIDFILE ]]; then
    if [[ "$1" =~ \/state\/ ]]; then
        kill -USR2 $(cat $PIDFILE)
    else
        kill -USR1 $(cat $PIDFILE)
    fi
fi

It checks if the modified file lives in /state subdirectory and if true does hot restart or else hot reload. I call the script like that:

while true
do
    find lib/ -name '*.dart' | entr -d -p ./hotreloader.sh /_
done

The /_ parameter makes entr to pass the name of the file to the program being invoked.