QCoreApplication QMetaCallEvent Compression Every queued slot call ends up in the posting of a QMetaCallEvent to the target object. The event contains the sender object, the signal id, the slot index, and packaged call parameters. On Qt 5, the signal id generally doesn’t equal the value returned by QMetaObject::signalIndex(): it is an index computed as … Read more
Add Q_OBJECT to your class, like this: class MainWidget : public QWidget { Q_OBJECT You also have to run moc to generate some helper code. qmake does that automatically for your, but if you compile this yourself, you need to run moc.
There are quite a few problems with your code : like said by Evan the emit keyword is missing all your objects live in the main thread, only the code in the run methods live in other threads, which means that the MySlot slot would be called in the main thread and I’m not sure … Read more
Signals as entities are created each time you invoke it as they represent a different connection: In [1]: import sys In [2]: from PyQt5 import QtWidgets In [3]: app = QtWidgets.QApplication(sys.argv) In [4]: button = QtWidgets.QPushButton() In [5]: id(button.clicked) Out[5]: 140150155639464 In [6]: id(button.clicked) Out[6]: 140150154507528 In [7]: id(button.clicked) Out[7]: 140150155640184 In [8]: id(button.clicked) Out[8]: … Read more
You won’t see much of a difference unless you’re working with objects having different thread affinities. Let’s say you have QObjects A and B and they’re both attached to different threads. A has a signal called somethingChanged() and B has a slot called handleChange(). If you use a direct connection connect( A, SIGNAL(somethingChanged()), B, SLOT(handleChange()), … Read more
As I found out in the last days… the Qt way of doing this is like this: class IEmitSomething { public: virtual ~IEmitSomething(){} // do not forget this signals: // <- ignored by moc and only serves as documentation aid // The code will work exactly the same if signals: is absent. virtual void someThingHappened() … Read more
Put the loop variable in a default argument, like this: lambda state, instance=instance: findInstance.projectsInstance.myslot( “TWCH”, findInstance, instance.text(), instance.checkState(), instance) This will give each lambda its own local copy of the instance variable. EDIT Here’s a simple script that demonstrates how to use default lambda arguments: from PyQt4 import QtGui class Window(QtGui.QWidget): def __init__(self): QtGui.QWidget.__init__(self) layout … Read more
Deleting QObjects is usually safe (i.e. in normal practice; there might be pathological cases I am not aware of atm), if you follow two basic rules: Never delete an object in a slot or method that is called directly or indirectly by a (synchronous, connection type “direct”) signal from the object to be deleted. E.g. … Read more
There are some rules that make life with signals and slots easier and cover the most common reason for defective connections. If I forgot something please tell me. 1) Check the debug console output: When execution errors occur, the debug output can show you the reason. 2) Use the full signature of signal and slot: … Read more
The problem can be solved in 2 ways: Using lambda functions: In general: obj.signal.connect(lambda param1, param2, …, arg1=val1, arg2= value2, … : fun(param1, param2,… , arg1, arg2, ….)) def fun(param1, param2,… , arg1, arg2, ….): […] where: param1, param2, … : are the parameters sent by the signal arg1, arg2, …: are the extra parameters … Read more