I have some unusual question :
For visualization of packing progress i think about qprogressbar with two values in one bar - one showing bytes read, and another showing write-out bytes, which gives also imagine about compress ratio.
It is possible with QT4 ?
Also, I have very little experience with C++ coding, my current work is based on Python, PyQT4,
Yes it's possible, but you will have to implement your own "DualValueProgressbar" here you have an example, is not complete production code but it will point to you in the right direction.
A note before continue:
Will this you will be able to show two values in the bar, but show two colours in the same bar is a very different thing. So I'll recomend you to use two prograssbar for doing what you want, keep it simple.
Before see any code let me explain what I did.
Subclass QProgressBar
Add a variable member called self.__value_1. This will be the second value.
Override the method paintEvent in order to draw self.__value_1 inside the bar.
Recomendations:
Write code for establishing limits on the second value. (Minimun and maximun)
Write code for handle the format property.
Write code for habdle the aligment property.
This is the result:
Here is the code:
from PyQt4.QtGui import *
from PyQt4.QtCore import *
class DualValueProgressBar(QProgressBar):
def __init__(self, parent=None):
super(DualValueProgressBar, self).__init__(parent)
# The other value you want to show
self.__value_1 = 0
def paintEvent(self, event):
# Paint the parent.
super(DualValueProgressBar, self).paintEvent(event)
# In the future versions if your custom object you
# should use this to set the position of the value_1
# in the progressbar, right now I'm not using it.
aligment = self.alignment()
geometry = self.rect() # You use this to set the position of the text.
# Start to paint.
qp = QPainter()
qp.begin(self)
qp.drawText(geometry.center().x() + 20, geometry.center().y() + qp.fontMetrics().height()/2.0, "{0}%".format(str(self.value1)))
qp.end()
#property
def value1(self):
return self.__value_1
#pyqtSlot("int")
def setValue1(self, value):
self.__value_1 = value
if __name__ == '__main__':
import sys
app = QApplication(sys.argv)
window = QWidget()
hlayout = QHBoxLayout(window)
dpb = DualValueProgressBar(window)
dpb.setAlignment(Qt.AlignHCenter)
# This two lines are important.
dpb.setValue(20)
dpb.setValue1(10) # Look you can set another value.
hlayout.addWidget(dpb)
window.setLayout(hlayout)
window.show()
sys.exit(app.exec())
Finally the code sample:
Related
Updated Question
I think my original quandary might be a result of the structure of my PyQt app. The way I've approached creating a GUI is to divide the larger widget into smaller pieces, each given their own class until the parts are simple enough. Because of this, I end up with a ton of nesting, as a large widget holds instances of smaller widgets, and those hold their own even smaller widgets. It makes it hard to navigate data around the app.
How should a PyQt app be structured so that it is simple to understand in code and yet has a structure containing very little nesting? I haven't found many examples of this around, so I'm sort of stuck. The code example in my original question shows a pretty good example of the structure I'm currently using, which has a large amount of nesting.
Info on program
The GUI is used to create a set of parameters for running a test. The options in each setting should correspond to a binary number, and all of the binary numbers indicated by each set of options are collected, formed into a single sequence of binary numbers, and passed on. Changes to settings do not have to be carried over between sessions, as each new session will most likely correspond to a new test (and thus a new set of choices for settings).
The basic flow of the app should be that upon opening it, all available settings (about 20 total) are set to their default values. A user can go through and change whatever settings they would like, and once they're done they can press a "Generate" button to gather all of the binary numbers corresponding to the settings and create the command. It would be very helpful to have a live preview of individual bits that updates as settings are changed, which is why updates must be immediate.
Some settings are dependent on other; for instance, Setting A has 4 options, and if option 3 is selected, Setting B should be made visible, otherwise it is invisible.
Original Question
I'm definitely a beginner to PyQt, so I don't quite know if I've worded my question correctly, but here goes. I've got a GUI wherein I'm attempting to take a bunch of different settings, keep track of what number was selected from each setting, and then pass the number up to an object that keeps track of all of the numbers from all of the settings. The trouble is that I don't know the best way to get all the individual settings values up my tree of classes, so to speak. Here's the structure of my GUI so far:
Bottom: individual custom QWidgets, each responsible for a single setting. Each has a signal that fires whenever the value it returns changes.
Middle: a QWidget containing ~7-10 individual settings each. These collect settings into related groups.
Top: a QTabWidget that places each instance of a setting group into an individual tab. This widget also contains an object that should ideally collect all of the settings from individual groups into it.
My question is how do I get the values from the bottom layer signals to the top layer widget? My only idea is to connect all of the signals from those small setting widgets to a signal in the middle layer, and connect the middle layer signal to something in the top layer. This sort of chaining seems crazy, though.
I'm running PyQt5 and Python 3.7.
Here's some stripped down code which hopefully shows what I want to do.
class TabWindow(QTabWidget):
def __init__(self):
super().__init__()
self.tabs = [SettingsGroup1, SettingsGroup2, SettingsGroup3]
self.setting_storage = { # dictionary is where I'd like to store all settings values
# 'setting name': setting value
}
for tab in self.tabs:
self.addTab(tab, 'Example')
class SettingsGroup(QWidget):
def __init__(self):
super().__init__()
# not shown: layout created for widget
self.settings = []
def add_to_group(self, new_setting):
self.settings.append(new_setting)
# not shown: add setting to the layout
class SettingsGroup1(SettingsGroup):
def __init__(self):
super().__init__()
self.add_to_group([Setting1, Setting2, Setting3])
class SettingsGroup2(SettingsGroup):...
class SettingsGroup3(SettingsGroup):...
class Setting(QWidget):
val_signal = pyqtSignal([int], name='valChanged')
def __init__(self, name):
self.val = None
self.name = name
def set_val(self, new_val):
self.val = new_val
self.val_signal.emit(self.val) # <-- the signal I want to pass up
class Setting1(Setting):
def __init__(self, name):
super().__init__(name)
# not shown: create custom setting layout/interface
class Setting2(Setting):...
class Setting3(Setting):...
I use a lot of inheritance (SettingsGroup -> SettingsGroup1, 2, 3) because each subclass will have its own functions and internal dependencies that are unique to it. For each Setting subclass, for instance, there is a different user interface.
Thanks for any help provided!
EDIT: The question has been updated in the meantime, I've added a solution that's more specific at the bottom of this answer.
I feel like this question is slightly "opinion based", but since I've had my share of similar situations I'd like to propose my suggestions. In these situations it's important to understand that there's not one good way to do things, but many ways to do it wrong.
Original answer
An idea could be to create a common signal interface for every "level", which will get that signal and send it back to its parent by adding its own name to keep track of the setting "path"; the topmost widget will then evaluate the changes accordingly.
In this example every tab "group" has its own valueChanged signal, which includes the group name, setting name and value; the source signal is fired from the "source" (a spinbox, in this case), then it follows its parents which, in turn "add" their name in turn.
Keep in mind that you can also just use a generalized pyqtSignal(object) for every parent and connect it with widget.valueChanged.connect(self.valueChanged), and then track its group and setting by walking by self.sender() parents backwards.
As a final notice, if you are using these values for application settings, remember that Qt already provides the QSettings API, which can be used as a common and OS-transparent interface for every configuration you need to set (and remember between sessions) in your application. I implemented it in the example, but I suggest you to read its documentation to better understand how it works.
import sys
from PyQt5 import QtCore, QtWidgets
class SettingWidget(QtWidgets.QWidget):
valueChanged = QtCore.pyqtSignal(int)
def __init__(self, name):
super().__init__()
self.settings = QtCore.QSettings()
self.val = 0
self.name = name
layout = QtWidgets.QVBoxLayout()
self.setLayout(layout)
layout.addWidget(QtWidgets.QLabel(self.name))
self.spinBox = QtWidgets.QSpinBox()
layout.addWidget(self.spinBox)
self.spinBox.valueChanged.connect(self.set_val)
def set_val(self, new_val):
if self.val != new_val:
self.val = new_val
self.valueChanged.emit(self.val)
# enter a setting group, ensuring that same name settings won't
# be mismatched; this allows a single sub level setting only
self.settings.beginGroup(self.parent().name)
self.settings.setValue(self.name, new_val)
# leave the setting group. THIS IS IMPORTANT!!!
self.settings.endGroup()
class SettingWidget1(SettingWidget):
def __init__(self):
super().__init__('Setting1')
class SettingWidget2(SettingWidget):
def __init__(self):
super().__init__('Setting2')
class SettingWidget3(SettingWidget):
def __init__(self):
super().__init__('Setting3')
class SettingsGroup(QtWidgets.QWidget):
# create two signal signatures, the first sends the full "path",
# while the last will just send the value
valueChanged = QtCore.pyqtSignal([str, str, int], [int])
def __init__(self, name):
super().__init__()
self.name = name
layout = QtWidgets.QHBoxLayout()
self.setLayout(layout)
def add_to_group(self, new_setting):
widget = new_setting()
# emit both signal signatures
widget.valueChanged.connect(
lambda value, name=widget.name: self.valueChanged.emit(
self.name, name, value))
widget.valueChanged.connect(self.valueChanged[int])
self.layout().addWidget(widget)
class SettingsGroup1(SettingsGroup):
def __init__(self):
super().__init__('Group1')
self.add_to_group(SettingWidget1)
self.add_to_group(SettingWidget2)
class SettingsGroup2(SettingsGroup):
def __init__(self):
super().__init__('Group2')
self.add_to_group(SettingWidget3)
class TabWidget(QtWidgets.QTabWidget):
def __init__(self):
QtWidgets.QTabWidget.__init__(self)
self.settings = QtCore.QSettings()
self.tabs = [SettingsGroup1, SettingsGroup2]
self.settingsDict = {}
for tab in self.tabs:
widget = tab()
self.addTab(widget, widget.__class__.__name__)
widget.valueChanged[str, str, int].connect(self.valueChangedFullPath)
widget.valueChanged[int].connect(self.valueChangedOnly)
def valueChangedFullPath(self, group, setting, value):
# update the settings dict; if the group key doesn't exist, create it
try:
self.settingsDict[group][setting] = value
except:
self.settingsDict[group] = {setting: value}
settingsData = [group, setting, value]
print('Full path result: {}'.format(settingsData))
# Apply setting from here, instead of using the SettingWidget
# settings.setValue() option; this allows a single sub level only
# self.applySetting(data)
def valueChangedOnly(self, value):
parent = sender = self.sender()
# sender() returns the last signal sender, so we need to track down its
# source; keep in mind that this is *not* a suggested approach, as
# tracking the source might result in recursion if the sender's sender
# is not one of its children; this system also has issues if you're
# using a Qt.DirectConnection from a thread different from the one that
# emitted it
while parent.sender() in sender.children():
parent = sender.sender()
widgetPath = []
while parent not in self.children():
widgetPath.insert(0, parent)
parent = parent.parent()
settingsData = [w.name for w in widgetPath] + [value]
print('Single value result: {}'.format(settingsData))
# similar to valueChangedFullPath(), but with this implementation more
# nested "levels" can be used instead
# self.applySetting(settingsData)
def applySetting(self, settingsData):
# walk up to the next to last of settingsData levels, assuming they are
# all parent group section names
for count, group in enumerate(settingsData[:-2], 1):
self.settings.beginGroup(group)
# set the setting name settingsData[-2] to its value settingsData[-1]
self.settings.setValue(*settingsData[-2:])
for g in range(count):
self.settings.endGroup()
if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
# set both Organization and Application name to make settings persistent
app.setOrganizationName('StackOverflow')
app.setApplicationName('Example')
w = TabWidget()
w.show()
sys.exit(app.exec_())
Alternate solution, based on updated answer
Since the answer has become more specific in its update, I'm adding another suggestion.
As far as we can understand now, you don't need that level of "nested" classes, but more specifically designed code that can be reused according to your purposes. Also, since you're using binary based data, it makes things a bit (pun intended) easier, as long as you know how bit operation works (which I assume you do) and the setting "widgets" don't require specific GUI customization.
In this example I created just one "setting" class and one "group" class, and their instancies are created only according to their names and default values.
import sys
from PyQt5 import QtCore, QtWidgets
defaultValues = '0010101', '1001010', '000111'
# set bit lengths for each setting; be careful in ensuring that each
# setting group has the full default value bit length!
groups = [
['Group 1', [1, 3, 2, 1]],
['Group 2', [1, 2, 2, 1, 1]],
['Group 1', [2, 1, 2, 1]],
]
class BinaryWidget(QtWidgets.QFrame):
changed = QtCore.pyqtSignal()
def __init__(self, name, index, defaults='0'):
QtWidgets.QFrame.__init__(self)
self.setFrameShape(self.StyledPanel|self.Sunken)
layout = QtWidgets.QGridLayout()
self.setLayout(layout)
self.index = index
self.defaults = defaults
self.buttons = []
# use the "defaults" length to create buttons
for i in range(len(defaults)):
value = int(defaults[i], 2) & 1
# I used QToolButtons as they're usually smaller than QPushButtons
btn = QtWidgets.QToolButton()
btn.setText(str(value))
layout.addWidget(btn, 1, i)
btn.setCheckable(True)
btn.setChecked(value)
btn.toggled.connect(self.changed)
# show the binary value on change, just for conveniency
btn.toggled.connect(lambda v, btn=btn: btn.setText(str(int(v))))
self.buttons.append(btn)
layout.addWidget(QtWidgets.QLabel(name), 0, 0, 1, layout.columnCount())
def value(self):
# return the correct value of all widget's buttons; they're reversed
# because of how bit shifting works
v = 0
for i, btn in enumerate(reversed(self.buttons)):
v += btn.isChecked() << i
# bit shift again, according to the actual "setting" bit index
return v << self.index
def resetValues(self):
oldValue = self.value()
self.blockSignals(True)
for i, value in enumerate(self.defaults):
self.buttons[i].setChecked(int(self.defaults[i], 2) & 1)
self.blockSignals(False)
newValue = self.value()
# emit the changed signal only once, and only if values actually changed
if oldValue != newValue:
self.changed.emit()
class Group(QtWidgets.QWidget):
changed = QtCore.pyqtSignal()
def __init__(self, name, defaults=None, lenghts=None):
QtWidgets.QWidget.__init__(self)
layout = QtWidgets.QHBoxLayout()
self.setLayout(layout)
self.name = name
self.bitLength = 0
self.widgets = []
if defaults is not None:
self.addOptions(defaults, lenghts)
def value(self):
v = 0
for widget in self.widgets:
v += widget.value()
return v
def addOption(self, name, index, default='0'):
widget = BinaryWidget(name, index, default)
self.layout().addWidget(widget)
self.widgets.append(widget)
widget.changed.connect(self.changed)
self.bitLength += len(default)
def addOptions(self, defaults, lenghts = None):
if lenghts is None:
lenghts = [1] * len(defaults)
# reverse bit order for per-setting indexing
defaultsIndex = 0
bitIndex = len(defaults)
for i, l in enumerate(lenghts):
self.addOption(
'Setting {}'.format(i + 1),
bitIndex - l,
defaults[defaultsIndex:defaultsIndex + l])
bitIndex -= l
defaultsIndex += l
def resetValues(self):
for widget in self.widgets:
widget.resetValues()
class Tester(QtWidgets.QWidget):
def __init__(self):
QtWidgets.QWidget.__init__(self)
layout = QtWidgets.QGridLayout()
self.setLayout(layout)
self.tabWidget = QtWidgets.QTabWidget()
layout.addWidget(self.tabWidget)
resultLayout = QtWidgets.QHBoxLayout()
layout.addLayout(resultLayout, layout.rowCount(), 0, 1, layout.columnCount())
self.tabs = []
self.labels = []
for (group, lenghts), defaults in zip(groups, defaultValues):
tab = Group(group, defaults, lenghts)
self.tabWidget.addTab(tab, group)
tab.changed.connect(self.updateResults)
self.tabs.append(tab)
tabLabel = QtWidgets.QLabel()
self.labels.append(tabLabel)
resultLayout.addWidget(tabLabel)
self.resetButton = QtWidgets.QPushButton('Reset values')
layout.addWidget(self.resetButton)
self.resetButton.clicked.connect(lambda: [tab.resetValues() for tab in self.tabs])
self.updateResults()
def values(self):
return [tab.value() for tab in self.tabs]
def updateResults(self):
for value, tab, label in zip(self.values(), self.tabs, self.labels):
label.setText('''
{0}: <span style="font-family:monospace;">{1} <b>{1:0{2}b}</b></span>
'''.format(tab.name, value, tab.bitLength))
if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
w = Tester()
w.show()
sys.exit(app.exec_())
I have implemented very simple syntax highlighter and I'm using it with the QTextEdit.
class MyHighlighter(QtGui.QSyntaxHighlighter):
def __init__(self, parent):
QtGui.QSyntaxHighlighter.__init__(self, parent)
self.Rules = []
classFormat = QtGui.QTextCharFormat()
classFormat.setFontWeight(QtGui.QFont.Bold)
classFormat.setForeground(QtCore.Qt.darkMagenta)
classFormat.setToolTip("this is very important!")
self.Rules.append(
('keyword', classFormat)
)
def highlightBlock(self, text):
for pattern, classFormat in self.Rules:
expression = re.compile(pattern)
for match in re.finditer(expression, text):
index = match.start()
length = match.end() - index
self.setFormat(index, length, classFormat)
Syntax highlighter correctly set text formatting but the tooltip isn't available. It simply never visible.
I found some a old bug report which describe a similar behaviour but looks there is no solution for mentioned issue:
https://bugreports.qt.io/browse/QTBUG-21553
How can I workaround this to get the tool tip working?
I was thinking that I can use html tags inside the QTextEdit. But I don't like that idea as it will add more complexity to text preprocessing (I'm working on big files). Also did some experiments with that and looks like it also could be tricky.
From what I remember in the bug tracker, the problem is that the widget's tooltip lookup doesn't get updated when the highlighter runs.
You can reimplement the tooltip lookup yourself like this (chopped down from some of my own code which uses QPlainTextEdit but I've confirmed to function the same if you %s/QPlainTextEdit/QTextEdit/g):
from PyQt5.QtCore import Qt, QEvent
from PyQt5.QtGui import QSyntaxHighlighter, QTextCharFormat, QTextCursor
from PyQt5.QtWidgets import QApplication, QPlainTextEdit, QToolTip
from nlprule import Tokenizer, Rules
class TooltipPlainTextEdit(QPlainTextEdit):
def __init__(self, *args):
QPlainTextEdit.__init__(self, *args)
self.setMouseTracking(True)
self.highlighter = NlpRuleHighlighter(self.document())
def event(self, event) -> bool:
"""Reimplement tooltip lookup to get nlprule messages working"""
if event.type() == QEvent.ToolTip:
pos = event.pos()
pos.setX(pos.x() - self.viewportMargins().left())
pos.setY(pos.y() - self.viewportMargins().top())
cursor = self.cursorForPosition(pos)
# QTextCursor doesn't have a quicker way to get
# highlighter-applied formats
for fmt in cursor.block().layout().formats():
if (fmt.start <= cursor.position() and
fmt.start + fmt.length >= cursor.position()):
cursor.setPosition(fmt.start)
cursor.setPosition(fmt.start + fmt.length,
QTextCursor.KeepAnchor)
QToolTip.showText(event.globalPos(), fmt.format.toolTip(),
self, self.cursorRect(cursor))
return True
return super(TooltipPlainTextEdit, self).event(event)
class NlpRuleHighlighter(QSyntaxHighlighter):
grammar_format = QTextCharFormat()
grammar_format.setUnderlineColor(Qt.blue)
grammar_format.setUnderlineStyle(QTextCharFormat.SpellCheckUnderline)
def __init__(self, *args):
QSyntaxHighlighter.__init__(self, *args)
self.nlprule_tokenizer = Tokenizer.load("en")
self.nlprule_rules = Rules.load("en", self.nlprule_tokenizer)
def highlightBlock(self, text: str):
for sugg in self.nlprule_rules.suggest(text):
self.grammar_format.setToolTip(sugg.message)
self.setFormat(sugg.start, sugg.end - sugg.start,
self.grammar_format)
if __name__ == '__main__': # pragma: nocover
import sys
app = QApplication(sys.argv)
edit = TooltipPlainTextEdit()
edit.show()
sys.exit(app.exec_())
In my preliminary "don't do more refactoring than I need to" testing, I found that this does preserve and assign the distinct messages like "Consider using the plural form here" and "Did you mean to have?" correctly, so I can only assume that QSyntaxHighlighter::setFormat makes a copy of self.grammar_format's state rather than taking a reference.
eyllanesc implemented something similar first, but he didn't actually do the lookup of what tooltip to display (thanks to user_none on QtCenter for pointing me in the right direction) and I didn't like how he was doing wordwise-select rather than working off the extents of the highlight. (Funny enough, in doing so, I answered the question in user7179690's comment here.)
I also did the margin correction that namezero pointed out the need for.
I want to create a callback for a slider. But since the slider I made is part of a groupbox function. I am not sure how I can connect it:
def createExampleGroup(self, name, interval, steps, min, max):
groupBox = QGroupBox(name)
slider = QSlider(Qt.Horizontal)
slider.setFocusPolicy(Qt.StrongFocus)
slider.setTickPosition(QSlider.TicksBothSides)
slider.setMinimum(min)
slider.setMaximum(max)
slider.setTickInterval(interval)
slider.setSingleStep(steps)
vbox = QVBoxLayout()
vbox.addWidget(slider)
# vbox.addStretch(1)
groupBox.setLayout(vbox)
return groupBox
def valueChange(self):
print ("Update Slider")
self.aGroup = self.createExampleGroup("SliderA",10,10,10,100)
self.bGroup = self.createExampleGroup("SliderB",10,10,10,100)
So I am not sure how I can access the slider in each group and connect them to valueChange. And also let valueChange() do different update based on which slider it is. I tried self.aGroup.findChild(QSlider) but it returns an address so I don't know how to use it. The reason I use group is that I may add other widgets in.
What findChild returns is the QSlider object, and you are probably printing it getting something similar to:
<PyQt5.QtWidgets.QSlider object at 0x7f6c521dedc8>
that's only what returns __str__, you can find more information in How to print objects of class using print()?.
So I could use that object
slider = self.aGroup.findChild(QSlider)
slider.valueChanged.connect(self.valueChange)
Although that option can be a little dirty, a better option from the design point of view is to create a class that inherits from QGroupBox and that shares the signal:
class MyGroupBox(QGroupBox):
valueChanged = pyqtSignal(int)
def __init__(self, name, interval, steps, min, max):
super(MyGroupBox, self).__init__(name)
slider = QSlider(Qt.Horizontal)
slider.setFocusPolicy(Qt.StrongFocus)
slider.setTickPosition(QSlider.TicksBothSides)
slider.setMinimum(min)
slider.setMaximum(max)
slider.setTickInterval(interval)
slider.setSingleStep(steps)
slider.valueChanged.connect(self.valueChanged)
vbox = QVBoxLayout()
vbox.addWidget(slider)
# vbox.addStretch(1)
self.setLayout(vbox)
Then you can use it in the following way:
self.aGroup = MyGroupBox("SliderA",10,10,10,100)
self.bGroup = MyGroupBox("SliderB",10,10,10,100)
self.aGroup.valueChanged.connect(self.valueChange)
The above gives an identity since it is a class that manifests certain properties by abstracting the internal elements.
There is several options available to you. You can simply return several widgets from your function:
def create_example_group(...) # python naming convention!
...
return group_box, slider
self.a_group, a_slider = self.create_example_group(...)
a_slider.changeValue.connect(...)
Alternative you could give slider a unique name and use findChildren or similar methods on your group-widget to find the widget.
I have a QGraphicsScene containing some simple objects (in this simplified example circles) that I want to change into other objects (here squares) when selected. More specifically I'd like to have parent objects which don't draw themselves, they are drawn by their child objects, and under various circumstances, but in particular when the parent objects are selected, I'd like the set of child objects to change. This is a nice conceptual framework for the overall app I am working on.
So I've implemented this in PySide and I thought it was working fine: the circles change nicely into squares when you click on them.
Until I use RubberBandDrag selection in the view. This causes an instant segfault when the rubber band selection reaches the parent object and the selection changes. Presumably this is being triggered because the rubber band selection in QT is somehow keeping a pointer to the child item which is disappearing before the rubber band selection action is complete.
Simplified code below - test it by first clicking on the object (it changes nicely) then dragging over the object - segfault:
from PySide import QtCore,QtGui
class SceneObject(QtGui.QGraphicsItem):
def __init__(self, scene):
QtGui.QGraphicsItem.__init__(self, scene = scene)
self.setFlag(QtGui.QGraphicsItem.ItemIsSelectable, True)
self.setFlag(QtGui.QGraphicsItem.ItemHasNoContents, True)
self.updateContents()
def updateContents(self):
self.prepareGeometryChange()
for c in self.childItems():
self.scene().removeItem(c)
if self.isSelected():
shape_item = QtGui.QGraphicsRectItem()
else:
shape_item = QtGui.QGraphicsEllipseItem()
shape_item.setFlag(QtGui.QGraphicsItem.ItemIsSelectable, False)
shape_item.setFlag(QtGui.QGraphicsItem.ItemStacksBehindParent,True)
shape_item.setPen(QtGui.QPen("green"))
shape_item.setRect(QtCore.QRectF(0,0,10,10))
shape_item.setParentItem(self)
def itemChange(self, change, value):
if self.scene() != None:
if change == QtGui.QGraphicsItem.ItemSelectedHasChanged:
self.updateContents()
return
return super(SceneObject,self).itemChange(change, value)
def boundingRect(self):
return self.childrenBoundingRect()
class Visualiser(QtGui.QMainWindow):
def __init__(self):
super(Visualiser,self).__init__()
self.viewer = QtGui.QGraphicsView(self)
self.viewer.setDragMode(QtGui.QGraphicsView.RubberBandDrag)
self.setCentralWidget(self.viewer)
self.viewer.setScene(QtGui.QGraphicsScene())
parent_item = SceneObject(self.viewer.scene())
parent_item.setPos(50,50)
app = QtGui.QApplication([])
mainwindow = Visualiser()
mainwindow.show()
app.exec_()
So questions:
Have I just made a mistake that can be straightforwardly fixed?
Or is removing objects from the scene not allowed when handling an ItemSelectedHasChanged event?
Is there a handy workaround? Or what's a good alternative approach? I could replace the QGraphicsRectItem with a custom item which can be drawn either as a square or a circle but that doesn't conveniently cover all my use cases. I can see that I could make that work but it will certainly not be as straightforward.
EDIT - Workaround:
It is possible to prevent this failing by preserving the about-to-be-deleted object for a while. This can be done by something like this:
def updateContents(self):
self.prepareGeometryChange()
self._temp_store = self.childItems()
for c in self.childItems():
self.scene().removeItem(c)
...
However, this is ugly code and increases the memory usage for no real benefit. Instead I have moved to using the QGraphicsScene.selectionChanged signal as suggested in this answer.
I've debugged it. Reproduced on Lunix
1 qFatal(const char *, ...) *plt 0x7f05d4e81c40
2 qt_assert qglobal.cpp 2054 0x7f05d4ea197e
3 QScopedPointer<QGraphicsItemPrivate, QScopedPointerDeleter<QGraphicsItemPrivate>>::operator-> qscopedpointer.h 112 0x7f05d2c767ec
4 QGraphicsItem::flags qgraphicsitem.cpp 1799 0x7f05d2c573b8
5 QGraphicsScene::setSelectionArea qgraphicsscene.cpp 2381 0x7f05d2c94893
6 QGraphicsView::mouseMoveEvent qgraphicsview.cpp 3257 0x7f05d2cca553
7 QGraphicsViewWrapper::mouseMoveEvent qgraphicsview_wrapper.cpp 1023 0x7f05d362be83
8 QWidget::event qwidget.cpp 8374 0x7f05d2570371
qt-everywhere-opensource-src-4.8.6/src/gui/graphicsview/qgraphicsscene.cpp:2381
void QGraphicsScene::setSelectionArea(const QPainterPath &path, Qt::ItemSelectionMode mode,
const QTransform &deviceTransform)
{
...
// Set all items in path to selected.
foreach (QGraphicsItem *item, items(path, mode, Qt::DescendingOrder, deviceTransform)) {
if (item->flags() & QGraphicsItem::ItemIsSelectable) { // item is invalid here
if (!item->isSelected())
changed = true;
unselectItems.remove(item);
item->setSelected(true);
}
}
They are using items() function to find a list of items under the rubber band selection. But if one item while processing deletes something the item pointer just becomes invalid. And next call to item->flags() causes the crash.
As alternative you could use QGraphicsScene::selectionChanged signal. It's emitted only once per selection change.
Looks like it's not expected by Qt to have some major changes in itemChange
Behind of this here is common mistake you have with prepareGeometryChange() call.
It's designed to be called right before changing boundingRect. Bounding rect should be the old one when prepareGeometryChange called and new one right after.
So that's could happen:
In updateContents:
self.prepareGeometryChange(); # calls boundingRect. old value returned
...
shape_item.setParentItem(self); # could call the boundingRect. but still old value returned!
After child added it calls boundingRect again but value unexpected different.
As a solution you can add a variable
def updateContents(self):
for c in self.childItems():
self.scene().removeItem(c)
if self.isSelected():
shape_item = QtGui.QGraphicsRectItem()
else:
shape_item = QtGui.QGraphicsEllipseItem()
shape_item.setFlag(QtGui.QGraphicsItem.ItemIsSelectable, False)
shape_item.setFlag(QtGui.QGraphicsItem.ItemStacksBehindParent,True)
shape_item.setPen(QtGui.QPen("green"))
shape_item.setRect(QtCore.QRectF(0,0,10,10))
shape_item.setParentItem(self)
self.prepareGeometryChange();
self._childRect = self.childrenBoundingRect()
def boundingRect(self):
return self._childRect
I want to create a doublespin box that changes values in steps of 0.2. But when the user enters a value that is not correct according to the steps. I normalizes that to the nearest correct value.
I tried something like the code shown below but I don't know how to stop values like 0.5 to be entered. Please help me on this.
from PyQt4.QtCore import *
from PyQt4.QtGui import *
class SigSlot(QWidget):
def __init__(self, parent=None):
QWidget.__init__(self, parent)
self.setWindowTitle('spinbox value')
self.resize(250,150)
self.lcd1 = QLCDNumber(self)
self.spinbox1 = QDoubleSpinBox(self)
self.spinbox1.setSingleStep(0.2)
self.spinbox1.setCorrectionMode(1)
# create a Grid Layout
grid = QGridLayout()
grid.addWidget(self.lcd1, 0, 0)
grid.addWidget(self.spinbox1, 1, 0)
self.setLayout(grid)
# allows access to the spinbox value as it changes
self.connect(self.spinbox1, SIGNAL('valueChanged(double)'), self.change_value1)
def change_value1(self, event):
val = self.spinbox1.value()
self.lcd1.display(val)
app = QApplication([])
qb = SigSlot()
qb.show()
app.exec_()
You have two choices:
You can subclass the QSpinBox, override validate method and use an appropriate Q*Validator (e.g. QRegExpValidator) inside.
You can check the value in slot connected to valueChanged before using and correct it if necessary.
Since you are already using the valueChanged signal, second option should be fairly easy to implement. Just change your change_value method like this:
def change_value1(self, val): # new value is passed as an argument
# so no need for this
# val = self.spinbox1.value()
new_val = round(val*5)/5 # one way to fix
if val != new_val: # if value is changed, put it in the spinbox
self.spinbox1.setValue(new_val)
self.lcd1.display(new_val)
By the way, since you are using only one decimal precision, it might be logical to also use:
self.spinbox1.setDecimals(1)
in your __init__. And try to use the new style signals and slots. i.e.:
self.connect(self.spinbox1, SIGNAL('valueChanged(double)'), self.change_value1)
could be written as:
self.spinbox1.valueChanged[float].connect(self.change_value1)
Edit
Subclassing:
class MySpinBox(QDoubleSpinBox):
def __init__(self, parent=None):
super(MySpinBox, self).__init__(parent)
# any RegExp that matches the allowed input
self.validator = QRegExpValidator(QRegExp("\\d+[\\.]{0,1}[02468]{0,1}"), self)
def validate(self, text, pos):
# this decides if the entered value should be accepted
return self.validator.validate(text, pos)
then instead of using QDoubleSpinBox you would use MySpinBox and leave the input checking to this class.
In your change value method you can do something like this
val = round(self.spinbox1.value(), 1)
if val/2*10 - int(val/2*10):
val = round(val, 1) + .1
It's probably not the best way but it works.