Creating a model/view interface with sliders using PyQt

Question

I have a GUI that consists of a number of sliders, and instead of updating the sliders manually when the underlying data changes, I'd like to store the data in a subclass of QAbstractListModel and have the slider positions update automatically. My subclass looks like this:

from PyQt4 import QtCore

class myDataModel(QtCore.QAbstractListModel):
    def __init__(self, initData, parent=None):
        super(myDataModel, self).__init__(parent)
        self.__data = initData

    def data(self, index, role=QtCore.Qt.DisplayRole):
        if not index.isValid():
            return None

        if index.row() > len(self.__data):
            return None

        if role == QtCore.Qt.DisplayRole or role == QtCore.Qt.EditRole:
            return self.__data[index.row()]

        return None

    def rowCount(self, parent=QtCore.QModelIndex()):
        return len(self.__data)

    def setData(self, index, value, role=QtCore.Qt.EditRole):
        if not index.isValid() or role != QtCore.Qt.EditRole:
            return False

        self.__data[index.row()] = value
        self.dataChanged.emit(index, index)
        return True

How can I connect this model to the sliders in my GUI so that when the data in the model is changed, the sliders change, and vice versa?

Edit: Here is a mockup of the basic interface I have been working on:

Edit: I still haven't been able to get this to work. Here is my model class:

class dataModel(QtCore.QAbstractListModel):

    def __init__(self, initData, parent=None):
        super(dataModel, self).__init__(parent)
        self.__data = initData

    def data(self, index, role=QtCore.Qt.DisplayRole):
        if not index.isValid():
            return None

        if index.row() > len(self.__data):
            return None

        if role == QtCore.Qt.DisplayRole or role == QtCore.Qt.EditRole:
            return self.__data[index.row()]

        return None

    def rowCount(self, parent=QtCore.QModelIndex()):
        return len(self.__data)

    def setData(self, index, value, role=QtCore.Qt.EditRole):
        if not index.isValid() or role != QtCore.Qt.EditRole:
            return False

        self.__data[index.row()] = value
        self.dataChanged.emit(index, index)
        return True

Here is the Delegate class:

class sliderDelegate(QtGui.QItemDelegate):
    '''
    classdocs
    '''
    def __init__(self, parent=None):
        '''
        Constructor
        '''
        super(sliderDelegate, self).__init__(parent)

    def setEditorData(self, editor, index):
        editor.setValue(index.model().data(index, QtCore.Qt.EditRole))

    def setModelData(self, editor, model, index):
        model.setData(index, editor.value(), QtCore.Qt.EditRole)

And here is the setup code:

self._model = dataModel([0 for i in xrange(20)])
self._parameterMapper = QtGui.QDataWidgetMapper(mainWindowInstance)
self._parameterMapper.setModel(self._model)
self._parameterMapper.setItemDelegate(sliderDelegate(mainWindowInstance))
self._parameterMapper.addMapping(self._mainWindowInstance.ui.mySlider, 0)
self._parameterMapper.toFirst()

Unfortunately I get the following error when toFirst() is called:

editor.setValue(index.model().data(index, QtCore.Qt.EditRole))
AttributeError: 'NoneType' object has no attribute 'data'

Any help would be appreciated.

Answer 1

So I haven't used QDataWidgetMapper. It does look interesting, but looks more useful for when you want to have multiple widgets updated to a particular row in a model (and be able to switch between rows easily), rather than each row of a model corresponding to the value of a widget (which I think is what you are after).

So this is my rather rough implementation. Hopefully you'll be able to extend it to your application (might need a bit more error checking added, and maybe the ability to link multiple sliders to a single model row, and possibly then extending to other types of widgets)

When you drag the slider, the model is updated to the sliders new value. I've also added a text box where you can type in a number, and click the button, which will set the model to a specific value. You will notice the slider will update to this value!

import sys

from PyQt4 import QtGui
from PyQt4 import QtCore

class MainWindow(QtGui.QWidget):
    def __init__(self):
        super(MainWindow, self).__init__()
        main_layout = QtGui.QVBoxLayout()

        # Create the model
        self.model = MyModel()

        # Create a slider and link it to the model
        self.slider1 = QtGui.QSlider()
        self.model.add_slider(self.slider1)        
        main_layout.addWidget(self.slider1)

        # Add a lineEdit and button to force update the model
        # Note that the LineEdit is not linked to the model, so won't update with the slider
        self.edit = QtGui.QLineEdit()
        button = QtGui.QPushButton('update model')
        button.clicked.connect(self.on_clicked)        
        main_layout.addWidget(self.edit)
        main_layout.addWidget(button)

        self.setLayout(main_layout)

    def on_clicked(self):
        self.model.update_model(int(self.edit.text()),self.slider1)

class MyModel(QtGui.QStandardItemModel):
    def __init__(self,*args,**kwargs):
        super(MyModel,self).__init__(*args,**kwargs)
        self._slider_list = {}
        self.itemChanged.connect(self.on_item_changed)

    def add_slider(self,slider):
        if slider in self._slider_list:
            raise Exception('You cannot link a slider to the model twice')

        item = QtGui.QStandardItem(str(slider.value()))
        self._slider_list[slider] = item
        self.appendRow(item)
        slider.valueChanged.connect(lambda value: self.update_model(value,slider))

    def update_model(self,value,slider):
        if str(value) != self._slider_list[slider].text():
            self._slider_list[slider].setText(str(value))
            print 'update_model: %d'%value

    def on_item_changed(self,item):
        slider = self._slider_list.keys()[self._slider_list.values().index(item)]
        if slider.value() != int(item.text()):
            slider.setValue(int(item.text()))
            print 'on_item_changed: %s'%item.text()

app = QtGui.QApplication(sys.argv)
window = MainWindow()
window.show()

sys.exit(app.exec_())

Hope that helps!