Fixing a Frozen Status Bar in PyQt4

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In one of my recent apps a long-running web request blocked the UI, so I wanted a status bar message to show what the background task was doing.

Multithreading approach

I had solved a similar problem before with a worker thread:

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class SetLabelText(QThread):
    def __init__(self, label, message, parent=None):
        super(SetLabelText, self).__init__(parent)
        self.label = label
        self.message = message
        
    def __del__(self):
        self.exiting = True
        self.wait()
        
    def run(self):
        self.label.setText(u"%s" % self.message)

And inside the time-consuming section:

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self.m1 = SetLabelText(self.status_label, u"Reminder")
self.m1.start()

A simpler option

Threads work, but when you update the status message multiple times in the same method you end up handling extra complexity. I found a simpler approach: update the label directly and immediately flush the event loop:

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self.status_label.setText(u"Loading configuration… please wait…")
QCoreApplication.processEvents()

Reference:

《How to use Qt multithreading correctly》