CODEWITHSUNDEEP
pythonmultithreadingqt
RPDeshaies
RPDeshaies

Reputation: 1874

Start a new thread in Python with a callback method in Main Thread for PyQT application

Situation :

I'm C#/JS developper and I'm new to Python. I'm developping a application using Python 2.7 and PyQT 4

In my main Window, I'm calling a method that is taking at least 15 seconds to execute.

This method is blocking my main thread and this is a problem for me because I want the user to be able to move the window even if the program is running calculation.

So I thought about using thread but I want to be able to be notified when the thread has finished it's job to refresh the data on the window.

If I call a new function in the created thread, it will create a new thread and it is nos permitted to modify the QT GUI from a different thread than the Main one.

Question :

Is there a way to start a new Thread (not a process) that will run a method and call another method from the Main Thread once the process is over ?

Clearly, I want to be able to have a equivalence to the JavaScript.jQuery.ajax() in a Python Environnement.

Upvotes: 4

Views: 4708

Answers (1)

Yoann Quenach de Quivillic
Yoann Quenach de Quivillic

Reputation: 5326

You need to use QThread and signal and slots. QThread inherits from QObject, which allows to emit signals.

Upon the completion of the task, the QThread will emit a finished() signal

Edit

If you define a custom Thread like this:

class CustomThread(QtCore.QThread):
    def __init__(self, target, slotOnFinished=None):
        super(CustomThread, self).__init__()
        self.target = target
        if slotOnFinished:
            self.finished.connect(slotOnFinished)

    def run(self, *args, **kwargs):
        self.target(*args, **kwargs)

You will be able to do:

class MyCustomWidget(QtGui.QWidget):

    def __init__(self, parent=None):
        super(MyCustomWidget, self).__init__(parent)
        layout = QtGui.QVBoxLayout(self)
        button = QtGui.QPushButton("Start", self)
        layout.addWidget(button)    
        button.clicked.connect(self.onStart)
        self.actionthread = CustomThread(target=self.longAction, self.onFinished)

    def onFinished(self):
        # Do Something

    def longAction(self):
        time.sleep(3)

    def onStart(self): 
        self.actionthread.start()

Upvotes: 3

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