Creating a custom widget in PyQT5

I would like to know how one can create a custom widget in pyqt. I've seen many different examples for C++, and a couple non descript examples for pyqt, but nothing that really explains how to do it and implement it. There is especially no examples that basically aren't just modified qt-designer output, and I'm writing my code from scratch so that's not very helpful.

So far, the best example I could find was basically just someone modifying qt-designer code and not really explaining what any of it was doing.

Could someone please show me an example of how to create a custom widget?

Edit: I'm attempting to create a widget with an embedded QStackedWidget, and buttons on the bottom to cycle the pages.

I also planned on having a seperate widget for each page, but considering I can't actually accomplish step one, I figured I would cross that bridge when I get to it.

回答1:

In the following it is shown how to implement a QStackedWidget with 2 buttons, the basic idea is to layout the design, for this we analyze that a QVBoxLayout must be placed to place the QStackedWidget and another layout, this second layout will be a QHBoxLayout to have the buttons. Then we connect the signals that handle the transition between pages. Also in this example I have created 3 types of widgets that will be placed on each page.

from PyQt5.QtWidgets import *


class Widget1(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent=parent)
        lay = QVBoxLayout(self)
        for i in range(4):
            lay.addWidget(QPushButton("{}".format(i)))

class Widget2(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent=parent)
        lay = QVBoxLayout(self)
        for i in range(4):
            lay.addWidget(QLineEdit("{}".format(i)))

class Widget3(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent=parent)
        lay = QVBoxLayout(self)
        for i in range(4):
            lay.addWidget(QRadioButton("{}".format(i)))

class stackedExample(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent=parent)
        lay = QVBoxLayout(self)
        self.Stack = QStackedWidget()
        self.Stack.addWidget(Widget1())
        self.Stack.addWidget(Widget2())
        self.Stack.addWidget(Widget3())

        btnNext = QPushButton("Next")
        btnNext.clicked.connect(self.onNext)
        btnPrevious = QPushButton("Previous")
        btnPrevious.clicked.connect(self.onPrevious)
        btnLayout = QHBoxLayout()
        btnLayout.addWidget(btnPrevious)
        btnLayout.addWidget(btnNext)

        lay.addWidget(self.Stack)
        lay.addLayout(btnLayout)

    def onNext(self):
        self.Stack.setCurrentIndex((self.Stack.currentIndex()+1) % 3)

    def onPrevious(self):
        self.Stack.setCurrentIndex((self.Stack.currentIndex()-1) % 3)


if __name__ == '__main__':
    import sys
    app = QApplication(sys.argv)
    w = stackedExample()
    w.show()
    sys.exit(app.exec_())

回答2:

Here are some nice advises, examples and approaches.

I think you can divide a custom Widget or any Custom "thing" you want in three ways.

Behavior: When you override its default methods with the behavior you want.
Layout: All the qt objects, be Items, or Widgets you add inside the layout will follow it's position rules and its policies.
StyleSheet: In case of Widget objects where you set the style of the Widget let's say setting its "CSS", just to be concise. Here are some references and examples.

Note: In case of non Widget objects you will not be able to set a StyleSheet so you will have to override some paint methods, create your own Painters and so on.

Here are some random examples with some comments along approaching the 3 topics I mentioned above:

import random
import sys

from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QApplication
from PyQt5.QtWidgets import QDialog
from PyQt5.QtWidgets import QHBoxLayout
from PyQt5.QtWidgets import QPushButton
from PyQt5.QtWidgets import QVBoxLayout
from PyQt5.QtWidgets import QWidget



class MovableWidget(QWidget):

    def __init__(self):
        super(MovableWidget, self).__init__()

        #remove the frame
        self.setWindowFlags(Qt.CustomizeWindowHint)
        self.pressing = False

    # overriding the three next methods is a way to customize your Widgets
    # not just in terms of appearance but also behavioral.

    def mousePressEvent(self, QMouseEvent):
        #the pos of the widget when you first pressed it.
        self.start = QMouseEvent.pos()
        #to make sure you are holding mouse button down
        self.pressing = True

    def mouseMoveEvent(self, QMouseEvent):

        # You can Verify if it's also the left button and some other things
        # you need.
        if self.pressing : #and QMouseEvent.type() == Qt.LeftButton
            self.end = QMouseEvent.pos()
            self.delta = self.mapToGlobal(self.end-self.start)
            self.move(self.delta)
            self.end = self.start

    def mouseReleaseEvent(self, QMouseEvent):
        self.pressing = False

# inherits from QDialog and from MovableWidget so we can have its properties.
class CustomDialog(QDialog, MovableWidget):

    def __init__(self):
        super(CustomDialog, self).__init__()

        #Make the Dialog transparent
        self.setAttribute(Qt.WA_TranslucentBackground)

        # the widget will dispose itself according to the layout rules he's
        # inserted into.
        self.inner_widget = QWidget()
        self.inner_widget.setFixedSize(300,300)
        self.inner_layout = QHBoxLayout()
        self.inner_widget.setLayout(self.inner_layout)

        self.btn_change_color = QPushButton("Roll Color")

        self.btn_change_color.setStyleSheet("""
            background-color: green;
        """)

        # will connect to a function to be executed when the button is clicked.
        self.btn_change_color.clicked.connect(self.change_color)
        self.inner_layout.addWidget(self.btn_change_color)

        # Choose among many layouts according to your needs, QVBoxLayout,
        # QHBoxLayout, QStackedLayout, ... you can set its orientation
        # you can set its policies, spacing, margins. That's one of the main
        # concepts you have to learn to customize your Widget in the way
        # you want.
        self.layout = QVBoxLayout()

        # stylesheet have basically CSS syntax can call it QSS.
        # it can be used only on objects that come from Widgets
        # Also one of the main things to learn about customizing Widgets.

        # Note: The stylesheet you set in the "father" will be applied to its
        # children. Unless you tell it to be applied only to it and/or specify
        # each children's style.

        # The point I used inside the StyleSheet before the QDialog
        # e.g .QDialog and .QWidget says it'll be applied only to that
        # instance.

        self.setStyleSheet("""
            .QDialog{
                border-radius: 10px;
            }
        """)
        self.inner_widget.setStyleSheet("""
            .QWidget{
                background-color: red;
            }
        """)


        self.layout.addWidget(self.inner_widget)
        self.setLayout(self.layout)

    def change_color(self):
        red = random.choice(range(0,256))
        green = random.choice(range(0,256))
        blue = random.choice(range(0,256))
        self.inner_widget.setStyleSheet(
        """
            background-color: rgb({},{},{});
        """.format(red,green,blue)
        )

# since MovableWidget inherits from QWidget it also have QWidget properties.
class ABitMoreCustomizedWidget(MovableWidget):

    def __init__(self):
        super(ABitMoreCustomizedWidget, self).__init__()

        self.layout = QHBoxLayout()
        self.setLayout(self.layout)

        self.custom_button1 = CustomButton("Button 1")
        self.custom_button1.clicked.connect(self.btn_1_pressed)
        self.custom_button2 = CustomButton("Button 2")
        self.custom_button2.clicked.connect(self.btn_2_pressed)

        self.layout.addWidget(self.custom_button1)
        self.layout.addWidget(self.custom_button2)

    def btn_1_pressed(self):
        self.custom_button1.hide()
        self.custom_button2.show()

    def btn_2_pressed(self):
        self.custom_button2.hide()
        self.custom_button1.show()

class CustomButton(QPushButton):

    # it could receive args and keys** so all the QPushButton initializer
    # would work for here too.
    def __init__(self, txt):
        super(CustomButton, self).__init__()
        self.setText(txt)
        self.setStyleSheet("""
            QPushButton{
                background-color: black;
                border-radius: 5px;
                color: white;
            }
            QPushButton::pressed{
                background-color: blue;
            }
            QPushButton::released{
                background-color: gray;
            }
        """)

if __name__ == "__main__":
    app = QApplication(sys.argv)
    custom_dialog = CustomDialog()
    custom_widget = ABitMoreCustomizedWidget()
    custom_dialog.show()
    custom_widget.show()
    sys.exit(app.exec_())

Tips:

You are also able to make use of masks in your widget changing it's format in "crazy" ways. For example if you need a hollow ringed widget you can have a image with this format and some transparency, create a QPixMap from that and apply it as a mask to your widget. Not a trivial work but kind of cool.

Since I showed you examples with no "TopBar" with no Frame you can also have a look in this other question where I show how to create your own top bar, move around and resize concepts.