Writing Gui Clients

Introduction

This page describes how to write GUI clients using the PyQt4 Python library. We assume some familiarity with PyQt, please see this tutorial for an excellent introduction for writing PyQt programs. We explain how to create a LabRAD client that encompasses a graphical user interface containing, buttons, spinboxes, dropdown menus, and any other PyQt widgets. The created clients are similar scripts in that they interface with a server and are able to execute server settings in response to user action i.e pressing a button. In addition, the GUI clients are able subscribe to signals from the server and act in response to these signals being emitted. For these reasons, GUI clients are referred to as asynchronous clients.

Common event loop

LabRAD is built on top of the twisted Python library. In twisted, the timing of all events is controlled by an event loop called a reactor. Similarly to twisted, PyQt has its own reactor to control the timing graphical events. For the two libraries to work together, the two event loops must be combined. This is done with a freely available (qt4reactor)[https://github.com/ghtdak/qtreactor/blob/master/qt4reactor.py] as follows: `` from PyQt4 import QtGui, uic from twisted.internet.defer import inlineCallbacks import os

SIGNALID = 874193

class pmtWidget(QtGui.QWidget): def init(self, reactor, parent=None): super(pmtWidget, self).init(parent) self.reactor = reactor basepath = os.path.dirname(file) path = os.path.join(basepath,"qtui", "pmtfrontend.ui") uic.loadUi(path,self) self.connect()

@inlineCallbacks
def connect(self):
    from labrad.wrappers import connectAsync
    from labrad import types as T
    self.T = T
    cxn = yield connectAsync()
    self.server = cxn.normalpmtflow
    yield self.initializeContent()
    yield self.setupListeners()
    #connect functions
    self.pushButton.toggled.connect(self.on_toggled)
    self.newSet.clicked.connect(self.onNewSet)
    self.doubleSpinBox.valueChanged.connect(self.onNewDuration)
    self.comboBox.currentIndexChanged.connect(self.onNewMode)

@inlineCallbacks
def setupListeners(self):
    yield self.server.signal__new_count(SIGNALID)
    yield self.server.signal__new_setting(SIGNALID + 1)
    yield self.server.addListener(listener = self.followSignal, source = None, ID = SIGNALID)
    yield self.server.addListener(listener = self.followSetting, source = None, ID = SIGNALID + 1)

@inlineCallbacks
def initializeContent(self):
    dataset = yield self.server.currentdataset()
    self.lineEdit.setText(dataset)
    running = yield self.server.isrunning()
    self.pushButton.setChecked(running)
    self.setText(self.pushButton)
    duration = yield self.server.get_time_length()
    try:
        ran = yield self.server.get_time_length_range()
    except Exception:
        #not able to obtain
        pass
    else:
        self.doubleSpinBox.setRange(*ran)
    mode = yield self.server.getcurrentmode()
    index = self.comboBox.findText(mode)
    self.comboBox.setCurrentIndex(index)
    self.lcdNumber.display('OFF')
    
    self.doubleSpinBox.setValue(duration)

def followSignal(self,signal,value):
    #print signal,value
    self.lcdNumber.display(value)

def followSetting(self, signal, message):
    setting,val = message
    if setting == "mode":
        index = self.comboBox.findText(val)
        self.comboBox.blockSignals(True)
        self.comboBox.setCurrentIndex(index)
        self.comboBox.blockSignals(False)
    if setting == 'dataset':
        self.lineEdit.blockSignals(True)
        self.lineEdit.setText(val)
        self.lineEdit.blockSignals(False)
    if setting == 'state':
        self.pushButton.blockSignals(True)
        if val =='on':
            self.pushButton.setChecked(True)
        else:
            self.pushButton.setChecked(False)
            self.lcdNumber.display('OFF')
        self.pushButton.blockSignals(False)
        self.setText(self.pushButton)
    if setting == 'timelength':
        self.doubleSpinBox.blockSignals(True)
        self.doubleSpinBox.setValue(float(val))
        self.doubleSpinBox.blockSignals(False)
        
@inlineCallbacks
def on_toggled(self, state):
    if state:
        yield self.server.record_data()
        newset = yield self.server.currentdataset()
        self.lineEdit.setText(newset)
    else:
        yield self.server.stoprecording()
        self.lcdNumber.display('OFF')
    self.setText(self.pushButton)

@inlineCallbacks
def onNewSet(self, x):
    newset = yield self.server.start_new_dataset()
    self.lineEdit.setText(newset)

@inlineCallbacks
def onNewMode(self, mode):
    text = str(self.comboBox.itemText(mode))
    yield self.server.set_mode(text)
    
def setText(self, obj):
    state = obj.isChecked()
    if state:
        obj.setText('ON')
    else:
        obj.setText('OFF')

def onNewData(self,count):
    self.lcdNumber.display(count)

@inlineCallbacks
def onNewDuration(self, value):
    value = self.T.Value(value, 's')
    yield self.server.set_time_length(value)

def closeEvent(self, x):
    self.reactor.stop()   

if name=="main": a = QtGui.QApplication( [] ) import qt4reactor qt4reactor.install() from twisted.internet import reactor pmtWidget = pmtWidget(reactor) pmtWidget.show() reactor.run() ``

Reactor already installed error

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