Cinnamon applet settings: display a setting value by choosing an option

applet.js

const Applet = imports.ui.applet;
const Settings = imports.ui.settings;

function MyApplet(metadata, orientation, panelHeight, instanceId) {
  this.settings = new Settings.AppletSettings(this, UUID, instanceId);
  this._init(orientation, panelHeight, instanceId);
}

MyApplet.prototype = Object.create(Applet.TextIconApplet.prototype, {
  _init: { value: function (orientation, panelHeight, instanceId) {
    Applet.TextIconApplet.prototype._init.call(this, orientation, panelHeight, instanceId);

    // 'webservice' is a combobox
    this.settings.bindProperty(Settings.BindingDirection.IN, 'webservice',
          'webservice', this.on_change_webservice);

    // 'location_id' is a entry field
    this.settings.bindProperty(Settings.BindingDirection.BIDIRECTIONAL, 'location_id',
          'location_id', this.on_change_location);

    // 'location_store' is a generic, default = {}
    this.settings.bindProperty(Settings.BindingDirection.OUT, 'locations_store',
          'locations_store');
  },

  on_change_webservice: function () {
    this.location_id = this.locations_store[this.webservice];
  },

  on_change_location: function () {
    let cache = this.locations_store;
    cache[this.webservice] = this.location_id;
    // save the complete Object to the key
    this.locations_store = cache;
  }
}

settings-schema.json

{
  "webservice":
  { "type": "combobox"
  , "default": "yahoo"
  , "description": "Weather data provider"
  , "options":
    { "Yahoo! Weather": "yahoo"
    , "OpenWeatherMap": "owm"
    }
  }
, "location_id":
  { "type": "entry"
  , "default": ""
  , "description": "Location ID"
  }
, "locations_store":
  { "type": "generic"
  , "default": {}
  }
}

XletSettingsWidgets.patch

--- /usr/share/cinnamon/cinnamon-settings/bin/XletSettingsWidgets.py
+++ /usr/share/cinnamon/cinnamon-settings/bin/XletSettingsWidgets_live_update.py
@@ -50,6 +50,7 @@
         self.handler = self.file_monitor.connect("changed", self.on_file_changed)
         self.file_changed_timeout = None
         self.resume_timeout = None
+        self.monitor_exeption = None
 
     def create(self, key, setting_type, uuid):
         try:
@@ -66,13 +67,13 @@
     def do_reload(self):
         self.settings.reload()
         for key in self.widgets.keys():
-            self.widgets[key].on_settings_file_changed()
+            if key != self.monitor_exeption:
+                self.widgets[key].on_settings_file_changed()
         self.file_changed_timeout = None
         return False
 
-    def pause_monitor(self):
-        self.file_monitor.cancel()
-        self.handler = None
+    def pause_monitor(self, exeption):
+        self.monitor_exeption = exeption
 
     def resume_monitor(self):
         if self.resume_timeout:
@@ -80,8 +81,7 @@
         self.resume_timeout = GObject.timeout_add(2000, self.do_resume)
 
     def do_resume(self):
-        self.file_monitor = self.file_obj.monitor_file(Gio.FileMonitorFlags.SEND_MOVED, None)
-        self.handler = self.file_monitor.connect("changed", self.on_file_changed)
+        self.monitor_exeption = None
         self.resume_timeout = None
         return False
 
@@ -133,7 +133,7 @@
     def save (self, name = None):
         if name is None:
             name = self.file_name
-        self.factory.pause_monitor()
+        self.factory.pause_monitor(None)
         if os.path.exists(name):
             os.remove(name)
         raw_data = json.dumps(self.data, indent=4)
@@ -148,7 +148,7 @@
         return key in self.data.keys()
 
     def real_update_dbus(self, key):
-        self.factory.pause_monitor()
+        self.factory.pause_monitor(key)
         session_bus = dbus.SessionBus()
         cinnamon_dbus = session_bus.get_object("org.Cinnamon", "/org/Cinnamon")
         setter = cinnamon_dbus.get_dbus_method('updateSetting', 'org.Cinnamon')

Settings are applied to the applet, but currently (Cinnamon 3.0) when the combobox option is changed, the entry field does only update after closing and re-opening the settings page.

XletSettingsWidgets.patch might be a possible patch.