1. Preference File Loading/Saving

Here is how to load and save preferences at launch and closing time.

Prerequisites
  • Preference file option must be set in the ScreenOptions widget.

  • Preference file path must be set in the INI configuration.

Reading preferences at launch time

Under the def initialized__(self): function add:

if self.w.PREFS_:
    # variable name (entry name, default value, type, section name)
    self.int_value = self.w.PREFS_.getpref('Integer_value', 75, int, 'CUSTOM_FORM_ENTRIES')
    self.string_value = self.w.PREFS_.getpref('String_value', 'on', str, 'CUSTOM_FORM_ENTRIES')
Writing preferences at close time

In the closing_cleanup__() function, add:

if self.w.PREFS_:
    # variable name (entry name, variable name, type, section name)
    self.w.PREFS_.putpref('Integer_value', self.integer_value, int, 'CUSTOM_FORM_ENTRIES')
    self.w.PREFS_.putpref('String_value', self.string_value, str, 'CUSTOM_FORM_ENTRIES')

2. Use QSettings To Read/Save Variables

Here is how to load and save variables using PyQt’s QSettings functions:

Good practices
  • Use Group to keep names organized and unique.

  • Account for none value returned when reading a setting which has no entry.

  • Set defaults to cover the first time it is run using the or _<default_value>_ syntax.

Note
The file is actually saved in ~/.config/QtVcp
Example

In this example:

  • We add or 20 and or 2.5 as defaults.

  • The names MyGroupName, int_value, float_value, myInteger, and myFloat are user defined.

  • Under the def initialized__(self): function add:

    # set recorded columns sort settings
    self.SETTINGS_.beginGroup("MyGroupName")
    self.int_value = self.SETTINGS_.value('myInteger', type = int) or 20
    self.float_value = self.SETTINGS_.value('myFloat', type = float) or 2.5
    self.SETTINGS_.endGroup()
  • Under the def closing_cleanup__(self): function add:

    # save values with QSettings
    self.SETTINGS_.beginGroup("MyGroupName")
    self.SETTINGS_.setValue('myInteger', self.int_value)
    self.SETTINGS_.setValue('myFloat', self.float_value)
    self.SETTINGS_.endGroup()

3. Add A Basic Style Editor

Being able to edit a style on a running screen is convenient.

Import StyleSheetEditor module in the IMPORT SECTION:
from qtvcp.widgets.stylesheeteditor import StyleSheetEditor as SSE
Instantiate StyleSheetEditor module in the INSTANTIATE SECTION:
STYLEEDITOR = SSE()
Create a keybinding in the INITIALIZE SECTION:

Under the +__init__.(self, halcomp, widgets, paths):+ function add:

KEYBIND.add_call('Key_F12','on_keycall_F12')
Create the key bound function in the KEYBINDING SECTION:
def on_keycall_F12(self,event,state,shift,cntrl):
    if state:
        STYLEEDITOR.load_dialog()

4. Request Dialog Entry

QtVCP uses STATUS messages to pop up and return information from dialogs.

Prebuilt dialogs keep track of their last position and include options for focus shading and sound.

To get information back from the dialog requires using a STATUS general message.

Import and Instantiate the Status module in the IMPORT SECTION
from qtvcp.core import Status
STATUS = Status()

This loads and initializes the Status library.

Register function for STATUS general messages in the INITIALIZE SECTION

Under the +__init__.(self, halcomp, widgets, paths)+ function:

STATUS.connect('general',self.return_value)

This registers STATUS to call the function self.return_value when a general message is sent.

Add entry dialog request function in the GENERAL FUNCTIONS SECTION
def request_number(self):
    mess = {'NAME':'ENTRY','ID':'FORM__NUMBER', 'TITLE':'Set Tool Offset'}
    STATUS.emit('dialog-request', mess)

The function

  • creates a Python dict with:

    • NAME - needs to be set to the dialogs unique launch name.
      NAME sets which dialog to request.
      ENTRY or CALCULATOR allows entering numbers.

    • ID - needs to be set to a unique name that the function supplies. ID should be a unique key.

    • TITLE sets the dialog title.

    • Arbitrary data can be added to the dict. The dialog will ignore them but send them back to the return code.

  • Sends the dict as a dialog-request STATUS message

Add message data processing function in the CALLBACKS FROM STATUS SECTION
# Process the STATUS return message from set-tool-offset
def return_value(self, w, message):
    num = message.get('RETURN')
    id_code = bool(message.get('ID') == 'FORM__NUMBER')
    name = bool(message.get('NAME') == 'ENTRY')
    if id_code and name and num is not None:
        print('The {} number from {} was: {}'.format(name, id_code, num))

This catches all general messages so it must check the dialog type and id code to confirm it’s our dialog.

In this case we had requested an ENTRY dialog and our unique id was FORM_NUMBER, so now we know the message is for us.

ENTRY or CALCULATOR dialogs return a float number.

5. Speak a Startup Greeting

This requires the espeak library installed on the system.

Import and Instantiate the Status in the IMPORT SECTION
from qtvcp.core import Status
STATUS = Status()
Emit spoken message in the INITIALIZE SECTION

Under the init.(self, halcomp, widgets, paths) function:

STATUS.emit('play-alert','SPEAK Please remember to oil the ways.')

SPEAK is a keyword: everything after it will be pronounced.

6. ToolBar Functions

Toolbar buttons and submenus are added in Qt Designer but the code to make them do something is added in the handler file.

To add a submenus in Qt Designer:

  • Add a Qaction by typing in the toolbar column then clicking the + icon on the right.

  • This will add a sub column that you need to type a name into.

  • Now the original Qaction will be a Qmenu instead.

  • Now erase the Qaction you added to that Qmenu, the menu will stay as a menu.

In this example we assume you added a toolbar with one submenu and three actions. These actions will be configured to create:

  • a recent file selection menu,

  • an about pop up dialog action,

  • a quit program action, and

  • a user defined function action.

The objectName of the toolbar button is used to identify the button when configuring it - descriptive names help.

Using the action editor menu, right click and select edit.
Edit the object name, text, and button type for an appropriate action.

In this example the:

  • submenu name must be menuRecent,

  • actions names must be actionAbout, actionQuit, actionMyFunction

Loads the toolbar_actions library in the IMPORT SECTION
from qtvcp.lib.toolbar_actions import ToolBarActions
Instantiate ToolBarActions module in the INSTANTIATE LIBRARY SECTION
TOOLBAR = ToolBarActions()
Configure submenus and actions in the SPECIAL FUNCTIONS SECTION

Under the def initialized__(self) function add:

TOOLBAR.configure_submenu(self.w.menuRecent, 'recent_submenu')
TOOLBAR.configure_action(self.w.actionAbout, 'about')
TOOLBAR.configure_action(self.w.actionQuit, 'Quit', lambda d:self.w.close())
TOOLBAR.configure_action(self.w.actionMyFunction, 'My Function', self.my_function)
Define the user function in the GENERAL FUNCTIONS SECTION
def my_function(self, widget, state):
    print('My function State = ()'.format(state))

The function to be called if the action "My Function" button is pressed.

7. Add HAL Pins That Call Functions

In this way you don’t need to poll the state of input pins.

Loads the Qhal library in the IMPORT SECTION
from qtvcp.core import Qhal

This is to allow access to QtVCP’s HAL component.

Instantiate Qhal in the INSTANTIATE LIBRARY SECTION
QHAL = Qhal()
Add a function that gets called when the pin state changes

Under the initialised__ function, make sure there is an entry similar to this:

##########################################
# Special Functions called from QtVCP
##########################################

# at this point:
# the widgets are instantiated.
# the HAL pins are built but HAL is not set ready
def initialized__(self):
    self.pin_cycle_start_in = QHAL.newpin('cycle-start-in',QHAL.HAL_BIT, QHAL.HAL_IN)
    self.pin_cycle_start_in.value_changed.connect(lambda s: self.cycleStart(s))
Define the function called by pin state change in the GENERAL FUNCTIONS SECTION
#####################
# general functions #
#####################

def cycleStart(self, state):
    if state:
        tab = self.w.mainTab.currentWidget()
        if  tab in( self.w.tab_auto,  self.w.tab_graphics):
            ACTION.RUN(line=0)
        elif tab == self.w.tab_files:
                self.w.filemanager.load()
        elif tab == self.w.tab_mdi:
            self.w.mditouchy.run_command()

This function assumes there is a Tab widget, named mainTab, that has tabs with the names tab_auto, tab_graphics, tab_filemanager and tab_mdi.

In this way the cycle start button works differently depending on what tab is shown.

This is simplified - checking state and error trapping might be helpful.

8. Add A Special Max Velocity Slider Based On Percent

Some times you want to build a widget to do something not built in.

The built in Max velocity slider acts on units per minute, here we show how to do on percent.

The STATUS command makes sure the slider adjusts if LinuxCNC changes the current max velocity.

valueChanged.connect() calls a function when the slider is moved.

In Qt Designer add a QSlider widget called mvPercent, then add the following code to the handler file:

#############################
# SPECIAL FUNCTIONS SECTION #
#############################

def initialized__(self):
    self.w.mvPercent.setMaximum(100)
    STATUS.connect('max-velocity-override-changed', \
        lambda w, data: self.w.mvPercent.setValue( \
            (data / INFO.MAX_TRAJ_VELOCITY)*100 \
            )
        )
    self.w.mvPercent.valueChanged.connect(self.setMVPercentValue)

#####################
# GENERAL FUNCTIONS #
#####################

def setMVPercentValue(self, value):
    ACTION.SET_MAX_VELOCITY_RATE(INFO.MAX_TRAJ_VELOCITY * (value/100.0))

9. Toggle Continuous Jog On and Off

Generally selecting continuous jogging is a momentary button, that requires you to select the previous jog increment after.

We will build a button that toggles between continuous jog and whatever increment that was already selected.

In Qt Designer:

  • Add an ActionButton with no action

  • Call it btn_toggle_continuous.

  • Set the AbstractButton property checkable to True.

  • Set the ActionButton properties incr_imperial_number and incr_mm_number to 0.

  • Use Qt Designer’s slot editor to use the button signal clicked(bool) to call form’s handler function toggle_continuous_clicked().
    See Using Qt Designer To Add Slots section for more information.

Then add this code snippets to the handler file under the initialized__ function:

# at this point:
# the widgets are instantiated.
# the HAL pins are built but HAL is not set ready
def initialized__(self):
    STATUS.connect('jogincrement-changed', \
        lambda w, d, t: self.record_jog_incr(d,t) \
        )
    # set a default increment to toggle back to
    self.L_incr = 0.01
    self.L_text = "0.01in"

In the GENERAL FUNCTIONS SECTION add:

#####################
# GENERAL FUNCTIONS #
#####################

# if it isn't continuous, record the latest jog increment
# and untoggle the continuous button
def record_jog_incr(self,d, t):
    if d != 0:
        self.L_incr = d
        self.L_text = t
        self.w.btn_toggle_continuous.safecheck(False)

In the CALLBACKS FROM FORM SECTION add:

#######################
# CALLBACKS FROM FORM #
#######################

def toggle_continuous_clicked(self, state):
    if state:
        # set continuous (call the actionbutton's function)
        self.w.btn_toggle_continuous.incr_action()
    else:
        # reset previously recorded increment
        ACTION.SET_JOG_INCR(self.L_incr, self.L_text)

10. Class Patch The File Manager Widget

Note
Class patching (monkey patching) is a little like black magic - so use it only if needed.

The File manager widget is designed to load a selected program in LinuxCNC. But maybe you want to print the file name first.

We can "class patch" the library to redirect the function call.

In the IMPORT SECTION add:

from qtvcp.widgets.file_manager import FileManager as FM

Here we are going to:

  1. Keep a reference to the original function (1) so we can still call it

  2. Redirect the class to call our custom function (2) in the handler file instead.

    ##########################################
    # Special Functions called from QtVCP    #
    ##########################################
    
    # For changing functions in widgets we can 'class patch'.
    # class patching must be done before the class is instantiated.
    def class_patch__(self):
        self.old_load = FM.load # keep a reference of the old function <1>
        FM.load = self.our_load # redirect function to our handle file function <2>
  3. Write a custom function to replace the original:
    This function must have the same signature as the original function.
    In this example we are still going to call the original function by using the reference to it we recorded earlier.
    It requires the first argument to be the widget instance, which in this case is self.w.filemanager (the name given in the Qt Designer editor).

    #####################
    # GENERAL FUNCTIONS #
    #####################
    
    def our_load(self,fname):
        print(fname)
        self.old_load(self.w.filemanager,fname)

Now our custom function will print the file path to the terminal before loading the file.
Obviously boring but shows the principle.

Note

There is another slightly different way to do this that can have advantages: you can store the reference to the original function in the original class.
The trick here is to make sure the function name you use to store it is not already used in the class.
super__ added to the function name would be a good choice.
We won’t use that in built in QtVCP widgets.

##########################################
# Special Functions called from QtVCP
##########################################

# For changing functions in widgets we can 'class patch'.
# class patching must be done before the class is instantiated.
def class_patch__(self):
    FM.super__load = FM.load # keep a reference of the old function in the original class
    FM.load = self.our_load # redirect function to our handle file function

#####################
# GENERAL FUNCTIONS #
#####################

def our_load(self,fname):
    print(fname)
    self.w.filemanager.super__load(fname)

11. Adding Widgets Programmatically

In some situation it is only possible to add widgets with Python code rather then using the Qt Designer editor.

When adding QtVCP widgets programmatically, sometimes there are extra steps to be taken.

Here we are going to add a spindle speed indicator bar and up-to-speed LED to a tab widget corner.
Qt Designer does not support adding corner widgets to tabs but PyQt does.

This is a cut down example from QtAxis screen’s handler file.

Import required libraries

First we must import the libraries we need, if they’re not already imported in the handler file:

  • QtWidgets gives us access to the QProgressBar,

  • QColor is for the LED color,

  • StateLED is the QtVCP library used to create the spindle-at-speed LED,

  • Status is used to catch LinuxCNC status information,

  • Info gives us information about the machine configuration.

############################
# **** IMPORT SECTION **** #
############################

from PyQt5 import QtWidgets
from PyQt5.QtGui import QColor
from qtvcp.widgets.state_led import StateLED as LED
from qtvcp.core import Status, Info
Instantiate Status and Info channels

STATUS and INFO are initialized outside the handler class so as to be global references (no self. in front):

##########################################
# **** instantiate libraries section **** #
###########################################

STATUS = Status()
INFO = Info()
Register STATUS monitoring function

For the spindle speed indicator we need to know the current spindle speed.
For this we register with STATUS to:

  • Catch the actual-spindle-speed-changed signal

  • Call the self.update_spindle() function

########################
# **** INITIALIZE **** #
########################
# Widgets allow access to widgets from the QtVCP files.
# At this point the widgets and HAL pins are not instantiated.
def __init__(self,halcomp,widgets,paths):
    self.hal = halcomp
    self.w = widgets
    self.PATHS = paths

    STATUS.connect('actual-spindle-speed-changed', \
        lambda w,speed: self.update_spindle(speed))
Add the widgets to the tab

We need to make sure the Qt Designer widgets are already built before we try to add to them.
For this, we add a call to self.make_corner_widgets() function to build our extra widgets at the right time, i.e. under the initialized__() function:

##########################################
# Special Functions called from QtScreen #
##########################################

# at this point:
# the widgets are instantiated.
# the HAL pins are built but HAL is not set ready
def initialized__(self):
    self.make_corner_widgets()
Create the widgets building functions

Ok let’s code the function to build the widgets and add them in the tab widget.
We are assuming there is a tab widget built with Designer called rightTab.

We are assuming there is a tab widget built with Qt Designer called rightTab.

#####################
# general functions #
#####################

def make_corner_widgets(self):
    # make a spindle-at-speed green LED
    self.w.led = LED()                                        # <1>
    self.w.led.setProperty('is_spindle_at_speed_status',True) # <2>
    self.w.led.setProperty('color',QColor(0,255,0,255))       # <3>
    self.w.led.hal_init(HAL_NAME = 'spindle_is_at_speed')     # <4>

    # make a spindle speed bar
    self.w.rpm_bar = QtWidgets.QProgressBar()                 # <5>
    self.w.rpm_bar.setRange(0, INFO.MAX_SPINDLE_SPEED)        # <6>

    # container
    w = QtWidgets.QWidget()                                   # <7>
    w.setContentsMargins(0,0,0,6)
    w.setMinimumHeight(40)

    # layout
    hbox = QtWidgets.QHBoxLayout()                            # <8>
    hbox.addWidget(self.w.rpm_bar)                            # <9>
    hbox.addWidget(self.w.led)                                # <9>
    w.setLayout(hbox)

    # add the container to the corner of the right tab widget
    self.w.rightTab.setCornerWidget(w)                        # <10>
  1. This initializes the basic StateLed widget and uses self.w.led as the reference from then on.

  2. Since the state LED can be used for many indications, we must set the property that designates it as a spindle-at-speed LED.

  3. This sets it as green when on.

  4. This is the extra function call required with some QtVCP widgets.
    If HAL_NAME is omitted it will use the widget’s objectName if there is one.
    It gives the special widgets reference to:

    self.HAL_GCOMP

    the HAL component instance

    self.HAL_NAME

    This widget’s name as a string

    self.QT_OBJECT_

    This widget’s PyQt object instance

    self.QTVCP_INSTANCE_

    The very top level parent of the screen

    self.PATHS_

    The instance of QtVCP’s path library

    self.PREFS_

    the instance of an optional preference file

    self.SETTINGS_

    the Qsettings object

  5. Initializes a PyQt5 QProgressBar.

  6. Sets the max range of the progress bar to the max specified in the INI.

  7. We create a QWidget
    Since you can only add one widget to the tab corner and we want two there, we must add both into a container.

  8. add a QHBoxLayout to the QWidget.

  9. Then we add our QProgress bar and LED to the layout.

  10. Finally we add the QWidget (with our QProgress bar and LED in it) to the tab widget’s corner.

Create the STATUS monitoring function

Now we build the function to actually update out the QProgressBar when STATUS updates the spindle speed:

########################
# callbacks from STATUS #
########################
def update_spindle(self, data):
    self.w.rpm_bar.setInvertedAppearance(bool(data<0))       # <1>
    self.w.rpm_bar.setFormat('{0:d} RPM'.format(int(data)))  # <2>
    self.w.rpm_bar.setValue(abs(data))                       # <3>
  1. In this case we chose to display left-to-right or right-to-left, depending if we are turning clockwise or anticlockwise.

  2. This formats the writing in the bar.

  3. This sets the length of the colored bar.

12. Update/Read Objects Periodically

Sometimes you need to update a widget or read a value regularly that isn’t covered by normal libraries.

Here we update an LED based on a watched HAL pin every 100 ms.

We assume there is an LED named led in the Qt Designer UI file.

Load the Qhal library for access to QtVCP’s HAL component

In the IMPORT SECTION add:

from qtvcp.core import Qhal
Instantiate Qhal

In the INSTANTIATE LIBRARY SECTION add:

QHAL = Qhal()

Now add/modify these sections to include code that is similar to this:

Register a function to be called at CYCLE_TIME period

This is usually every 100 ms.

########################
# **** INITIALIZE **** #
########################
# widgets allows access to widgets from the QtVCP files
# at this point the widgets and hal pins are not instantiated
def __init__(self,halcomp,widgets,paths):
    self.hal = halcomp
    self.w = widgets
    self.PATHS = paths

    # register a function to be called at CYCLE_TIME period (usually every 100 ms)
    STATUS.connect('periodic', lambda w: self.update_periodic())
Create the custom function to be called periodically
#####################
# general functions #
#####################
def update_periodic(self):
    data = QHAL.getvalue('spindle.0.is-oriented')
    self.w.led.setState(data)

13. External Control With ZMQ

QtVCP can automatically set up ZMQ messaging to send and/or receive remote messages from external programs.

It uses ZMQ’s publish/subscribe messaging pattern.

As always, consider security before letting programs interface though messaging.

13.1. ZMQ Messages Reading

Sometimes you want to control the screen with a separate program.

Enable reception of ZMQ messages

In the ScreenOptions widget, you can select the property use_receive_zmq_option.
You can also set this property directly in the handler file, as in this sample.

We assume the ScreenOptions widget is called screen_options in Qt Designer:

########################
# **** INITIALIZE **** #
########################
# widgets allows access to widgets from the QtVCP files
# at this point the widgets and hal pins are not instantiated
def __init__(self,halcomp,widgets,paths):
    # directly select ZMQ message receiving
    self.w.screen_options.setProperty('use_receive_zmq_option',True)

This allows an external program to call functions in the handler file.

Add a function to be called on ZMQ message reception

Let’s add a specific function for testing.
You will need to run LinuxCNC from a terminal to see the printed text.

#####################
# general functions #
#####################
def test_zmq_function(self, arg1, arg2):
    print('zmq_test_function called: ', arg1, arg2)
Create an external program sending ZMQ messages that will trigger function call

Here is a sample external program to call a function.
It alternates between two data sets every second.
Run this in a separate terminal from LinuxCNC to see the sent messages.

#!/usr/bin/env python3
from time import sleep

import zmq
import json

context = zmq.Context()
socket = context.socket(zmq.PUB)
socket.bind("tcp://127.0.0.1:5690")
topic = b'QtVCP'

# prebuilt message 1
# makes a dict of function to call plus any arguments
x = {                               # <1>
  "FUNCTION": "test_zmq_function",
  "ARGS": [True,200]
}
# convert to JSON object
m1 = json.dumps(x)

# prebuild message 2
x = {                               # <1>
  "FUNCTION": "test_zmq_function",
  "ARGS": [False,0],
}
# convert to JSON object
m2 = json.dumps(x)

if __name__ == '__main__':
    while True:
        print('send message 1')
        socket.send_multipart([topic, bytes((m1).encode('utf-8'))])
        sleep(ms(1000))

        print('send message 2')
        socket.send_multipart([topic, bytes((m2).encode('utf-8'))])
        sleep(ms(1000))
  1. Set the function to call and the arguments to send to that function.

You will need to know the signature of the function you wish to call. Also note that the message is converted to a JSON object. This is because ZMQ sends byte messages not Python objects. json converts Python objects to bytes and will be converted back when received.

13.2. ZMQ Messages Writing

You may also want to communicate with an external program from the screen.

In the ScreenOptions widget, you can select the property use_send_zmq_message. You can also set this property directly in the handler file, as in this sample.

We assume the ScreenOptions widget is called screen_options in Qt Designer:

Enable sending of ZMQ messages
########################
# **** INITIALIZE **** #
########################
# widgets allows access to  widgets from the QtVCP files
# at this point the widgets and hal pins are not instantiated
def __init__(self, halcomp,widgets,paths):
    # directly select ZMQ message sending
    self.w.screen_options.setProperty('use_send_zmq_option',True)

This allows sending messages to a separate program.
The message sent will depend on what the external program is expecting.

Create a function to send ZMQ messages

Let’s add a specific function for testing.
You will need to run LinuxCNC from a terminal to see the printed text.
Also, something needs to be added to call this function, such as a button click.

#####################
# general functions #
#####################
def send_zmq_message(self):
    # This could be any Python object JSON can convert
    message = {"name": "John", "age": 30}
    self.w.screen_options.send_zmq_message(message)
Use or create a program that will receive ZMQ messages

Here is a sample program that will receive the message and print it to the terminal:

import zmq
import json

# ZeroMQ Context
context = zmq.Context()

# Define the socket using the "Context"
sock = context.socket(zmq.SUB)

# Define subscription and messages with topic to accept.
topic = "" # all topics
sock.setsockopt(zmq.SUBSCRIBE, topic)
sock.connect("tcp://127.0.0.1:5690")

while True:
    topic, message = sock.recv_multipart()
    print('{} sent message:{}'.format(topic,json.loads(message)))

14. Sending Messages To Status Bar Or Desktop Notify Dialogs

There are several ways to report information to the user.

A status bar is used for short information to show the user.

Note
Not all screens have a status bar.
Status bar usage example
self.w.statusbar.showMessage(message, timeout * 1000)

timeout is in seconds and we assume statusbar is the Qt Designer set name of the widget.

You can also use the Status library to send a message to the notify library if it is enabled (usually set in ScreenOptions widget): this will send the message to the statusbar and the desktop notify dialog.

The messages are also recorded until the user erases them using controls. The users can recall any recorded messages.

There are several options:

STATUS.TEMPORARY_MESSAGE

Show the message for a short time only.

STATUS.OPERATOR_ERROR
STATUS.OPERATOR_TEXT
STATUS.NML_ERROR
STATUS.NML_TEXT

Example of sending an operator message:
STATUS.emit('error', STATUS.OPERATOR_ERROR, 'message')

You can send messages thru LinuxCNC’s operator message functions. These are usually caught by the notify system, so are equal to above. They would be printed to the terminal as well.

ACTION.SET_DISPLAY_MESSAGE('MESSAGE')
ACTION.SET_ERROR_MESSAGE('MESSAGE')

15. Catch Focus Changes

Focus is used to direct user action such as keyboard entry to the proper widget.

Get currently focused widget
fwidget = QtWidgets.QApplication.focusWidget()
if fwidget is not None:
    print("focus widget class: {} name: {} ".format(fwidget, fwidget.objectName()))
Get focused widget when focus changes
# at this point:
# the widgets are instantiated.
# the HAL pins are built but HAL is not set ready
def initialized__(self):
    QtWidgets.QApplication.instance().event_filter.focusIn.connect(self.focusInChanged)

#####################
# general functions #
#####################

def focusInChanged(self, widget):
    if isinstance(widget.parent(),type(self.w.gcode_editor.editor)):
        print('G-code Editor')
    elif isinstance(widget,type(self.w.gcodegraphics)):
        print('G-code Display')
    elif isinstance(widget.parent(),type(self.w.mdihistory) ):
        print('MDI History')

Notice we sometimes compare to widget, sometimes to widget.parent().

This is because some QtVCP widgets are built from multiple sub-widgets and the latter actually get the focus; so we need to check the parent of those sub-widgets.

Other times the main widget is what gets the focus, e.g., the G-code display widget can be set to accept the focus. In that case there are no sub-widgets in it, so comparing to the widget.parent() would get you the container that holds the G-code widget.