如何在功能结束之前让Items显示在QListWidget中？

Question

I want my QListWidget to update with the new item as it is added, but it only updates with all of the items once the function has ended. I have tried using update() and repaint() , but neither work. I actually had to use repaint() on the Widget itself just to get it to show up before the end, but none of the items do. Here is a brief view of the first item to add:

def runPW10(self):
    self.PWList.setVisible(True)
    self.PWList.setEnabled(True)

    # This repaint() has to be here for even the List to show up
    self.PWList.repaint()

    ....

    self.PWList.addItem('Executing Change Password Tool')

    # This does not help
    self.PWList.repaint()

    ....

There is more to the function, but it is long and this should include what it needed. Please let me know if more is required.

What am I doing wrong that makes this List not update as the item is added?

Answer 1

Add QApplication.processEvents() .

QCoreApplication.processEvents (QEventLoop.ProcessEventsFlags flags = QEventLoop.AllEvents)

Processes all pending events for the calling thread according to the specified flags until there are no more events to process.

You can call this function occasionally when your program is busy performing a long operation (eg copying a file).

Your widget originally will be shown but unresponsive. To make the application responsive, add processEvents() calls to some whenever you add an item.

Do keep in mind that this can affect performance a lot . This lets the whole application loop execute including any queued events. Don't add this to performance sensitive loops.

Also consider that this allows your user to interact with the application, so make sure that any interactions that can happen either are not allowed, such as somebutton.enabled(False) , or are handled gracefully, like a Cancel button to stop a long task.

See the original C++ docs for further information, since pyqt is a direct port.

Answer 2

To complete Drise's answer on this point:

Also consider that this allows your user to interact with the application, so make sure that any interactions that can happen either are not allowed, such as somebutton.enabled(False) , or are handled gracefully, like a Cancel button to stop a long task.

You may want to use the QEventLoop.ExcludeUserInputEvents flag this way: QCoreApplication.processEvents(QEventLoop.ExcludeUserInputEvents) to refresh the GUI while preventing the user to activate any widgets.

QEventLoop.ExcludeUserInputEvents

0x01

Do not process user input events, such as ButtonPress and KeyPress . Note that the events are not discarded; they will be delivered the next time processEvents() is called without the ExcludeUserInputEvents flag.