Opening second window from first one for QGIS Plugin development via Python

Question

I know, there are several posts about this specific topic (e.g. how to open second window in my plugin for QGIS?), but I am still struggling with some problems.

I have developed a plugin for QGIS 3.34.4 with the PluginBuilder. As one result I got the initial *.ui file and the corresponding *.py file.

I have create a second *.ui file using QTDesigner and converted it via pyuic5 to a *.py file. My problem: I am not able to start the second GUI using a push button in the first GUI.

Here is the *.py file created by the PluginBuilder:

# -*- coding: utf-8 -*-

import os

from qgis.PyQt import uic
from qgis.PyQt import QtWidgets
from PyQt5.QtWidgets import QFileDialog
from qgis.utils import iface

from .secondDialog import Ui_selectionDialog

# This loads your .ui file so that PyQt can populate your plugin with the elements from Qt Designer
FORM_CLASS, _ = uic.loadUiType(os.path.join(
    os.path.dirname(__file__), 'ShowSelectedAttribute_dialog_base.ui'))


class ShowSelectedAttributeDialog(QtWidgets.QDialog, FORM_CLASS):
    def __init__(self, parent=None):
        """Constructor."""
        super(ShowSelectedAttributeDialog, self).__init__(parent)
        # Set up the user interface from Designer through FORM_CLASS.
        # After self.setupUi() you can access any designer object by doing
        # self.<objectname>, and you can use autoconnect slots - see
        # http://qt-project.org/doc/qt-4.8/designer-using-a-ui-file.html
        # #widgets-and-dialogs-with-auto-connect
        self.setWindowTitle("Mein Plugin-Test")
        self.setupUi(self)
        self.pbSelection.clicked.connect(self.getFeature)
        self.pbExport.clicked.connect(self.exportFeature)
        self.labelOutputSelection.hide()
        self.labelOutputExport.hide()
        self.browsePath.clicked.connect(self.openSecondGUI)


    def getFeature(self):
        pass  

    def exportFeature(self):
        pass

    def openSecondGUI(self):
        secondDialog = Ui_selectionDialog()
        secondDialog.setupUi(secondDialog)

I have already shortened the script here.. The last two lines show one attempt to open the second GUI.

The second *.py file containing the second GUI is this one:

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'C:\Users\Sven Harpering\AppData\Roaming\QGIS\QGIS3\profiles\default\python\plugins\showselectedattribute\secondDialog.ui'
#
# Created by: PyQt5 UI code generator 5.15.4
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.


from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_selectionDialog(object):
    def setupUi(self, selectionDialog):
        selectionDialog.setObjectName("selectionDialog")
        selectionDialog.resize(400, 300)
        self.buttonBox = QtWidgets.QDialogButtonBox(selectionDialog)
        self.buttonBox.setGeometry(QtCore.QRect(30, 240, 341, 32))
        self.buttonBox.setOrientation(QtCore.Qt.Horizontal)
        self.buttonBox.setStandardButtons(QtWidgets.QDialogButtonBox.Cancel|QtWidgets.QDialogButtonBox.Ok)
        self.buttonBox.setObjectName("buttonBox")
        self.pbSelection = QtWidgets.QPushButton(selectionDialog)
        self.pbSelection.setGeometry(QtCore.QRect(30, 50, 271, 51))
        self.pbSelection.setObjectName("pbSelection")
        self.labelOutputSelection_2 = QtWidgets.QLabel(selectionDialog)
        self.labelOutputSelection_2.setGeometry(QtCore.QRect(40, 120, 571, 21))
        self.labelOutputSelection_2.setObjectName("labelOutputSelection_2")

        self.retranslateUi(selectionDialog)
        self.buttonBox.accepted.connect(selectionDialog.accept)
        self.buttonBox.rejected.connect(selectionDialog.reject)
        QtCore.QMetaObject.connectSlotsByName(selectionDialog)

    def retranslateUi(self, selectionDialog):
        _translate = QtCore.QCoreApplication.translate
        selectionDialog.setWindowTitle(_translate("selectionDialog", "Dialog"))
        self.pbSelection.setText(_translate("selectionDialog", "Daten vom selektierten Feature abfragen."))
        self.labelOutputSelection_2.setText(_translate("selectionDialog", "TextLabel"))

I have not changed anything here.

As you can see in the first code snippet, I have already imported the second *.py file via

from .secondDialog import Ui_selectionDialog

Now I'm running out of ideas on how to properly call the setupUI() method so that the second window also appears.

All tutorials that I have found are showing solutions using ".show()" or ".exec_()". However, these are not included after converting the *.ui to a *.py file via pyuic5.

Am I on a wrong path?

You mention "several posts about this specific topic" but have not provided links to them. — PolyGeo
– PolyGeo ♦, Commented Apr 1, 2024 at 21:23

Ben W · Accepted Answer · 2024-04-03 03:42:14Z

There are of course multiple ways to achieve this. The simplest would be to modify your first dialog .py file like so:

# -*- coding: utf-8 -*-

import os

from qgis.PyQt import uic
from qgis.PyQt import QtWidgets
from PyQt5.QtWidgets import QFileDialog
from qgis.utils import iface

from .secondDialog import Ui_selectionDialog

# This loads your .ui file so that PyQt can populate your plugin with the elements from Qt Designer
FORM_CLASS, _ = uic.loadUiType(os.path.join(
    os.path.dirname(__file__), 'ShowSelectedAttribute_dialog_base.ui'))


class ShowSelectedAttributeDialog(QtWidgets.QDialog, FORM_CLASS):
    def __init__(self, parent=None):
        """Constructor."""
        super(ShowSelectedAttributeDialog, self).__init__(parent)
        # Set up the user interface from Designer through FORM_CLASS.
        # After self.setupUi() you can access any designer object by doing
        # self.<objectname>, and you can use autoconnect slots - see
        # http://qt-project.org/doc/qt-4.8/designer-using-a-ui-file.html
        # #widgets-and-dialogs-with-auto-connect
        self.setWindowTitle("Mein Plugin-Test")
        self.setupUi(self)
        self.pbSelection.clicked.connect(self.getFeature)
        self.pbExport.clicked.connect(self.exportFeature)
        self.labelOutputSelection.hide()
        self.labelOutputExport.hide()
        self.browsePath.clicked.connect(self.openSecondGUI)


    def getFeature(self):
        pass  

    def exportFeature(self):
        pass

    def openSecondGUI(self):
        # Create an instance of the second dialog class
        second_dlg = SecondDialog(self)
        second_dlg.exec()
        # or second_dlg.show()

# Add this Class definition for your second dialog
class SecondDialog(QtWidgets.QDialog):
    def __init__(self, parent=None):
        super(SecondDialog, self).__init__(parent)
        self.dlg2 = Ui_selectionDialog()
        self.dlg2.setupUi(self)

You can have a look at this tutorial for more details, as it pretty much covers what you are trying to do.

And, yes- you need to use show() or exec(). These are methods inherited by multiple Qt widget classes- the fact that they are not included in the generated .py file is irrelevant. The main difference between them is that exec() starts a new event loop which blocks the rest of the application until the dialog is closed and the loop exits; show() does not.

See: https://stackoverflow.com/questions/35607412/qt-4-8-5-understanding-qmessagebox-exec-and-show

Which you use is up to you depending on your use case.

Finally, the naming of your button browsePath leads me to wonder if you are creating a dialog in order for the user to select a file path or something similar? If that is the case, I would strongly recommend looking at QFileDialog to avoid reinventing the wheel.

Thank you for your answer and your hin regarding the function browsePath. It was only an example :). — kopi
– kopi, Commented Apr 3, 2024 at 19:03

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