Added property to indicate if output device accepts commands

Instead of how this was previously done, it's now tied to the auth state.

CL-541

cura/PrinterOutput/NetworkedPrinterOutputDevice.py

@@ -1,3 +1,6 @@
+# Copyright (c) 2017 Ultimaker B.V.
+# Cura is released under the terms of the LGPLv3 or higher.
+
 from UM.Application import Application
 from UM.Logger import Logger
 

cura/PrinterOutputDevice.py

@@ -34,6 +34,7 @@ i18n_catalog = i18nCatalog("cura")
 class PrinterOutputDevice(QObject, OutputDevice):
     printersChanged = pyqtSignal()
     connectionStateChanged = pyqtSignal(str)
+    acceptsCommandsChanged = pyqtSignal()
 
     def __init__(self, device_id, parent = None):
         super().__init__(device_id = device_id, parent = parent)
@@ -49,6 +50,7 @@ class PrinterOutputDevice(QObject, OutputDevice):
         self._control_item = None
 
         self._qml_context = None
+        self._accepts_commands = False
 
         self._update_timer = QTimer()
         self._update_timer.setInterval(2000)  # TODO; Add preference for update interval
@@ -152,6 +154,17 @@ class PrinterOutputDevice(QObject, OutputDevice):
     def __del__(self):
         self.close()
 
+    @pyqtProperty(bool, notify=acceptsCommandsChanged)
+    def acceptsCommands(self):
+        return self._accepts_commands
+
+        ##  Set a flag to signal the UI that the printer is not (yet) ready to receive commands
+    def setAcceptsCommands(self, accepts_commands):
+        if self._accepts_commands != accepts_commands:
+            self._accepts_commands = accepts_commands
+
+        self.acceptsCommandsChanged.emit()
+
 
 ##  The current processing state of the backend.
 class ConnectionState(IntEnum):

plugins/UM3NetworkPrinting/LegacyUM3OutputDevice.py

@@ -65,6 +65,15 @@ class LegacyUM3OutputDevice(NetworkedPrinterOutputDevice):
         self._compressing_gcode = False
         self._gcode = []
 
+        self.authenticationStateChanged.connect(self._onAuthenticationStateChanged)
+
+    def _onAuthenticationStateChanged(self):
+        # We only accept commands if we are authenticated.
+        if self._authentication_state == AuthState.Authenticated:
+            self.setAcceptsCommands(True)
+        else:
+            self.setAcceptsCommands(False)
+
     def _setupMessages(self):
         self._authentication_requested_message = Message(i18n_catalog.i18nc("@info:status",
                                                                             "Access to the printer requested. Please approve the request on the printer"),