Pyqt main loop.
Pyqt main loop Apr 9, 2013 · You could also do the polling in a different thread and send signals to the main thread. In that example, the thread will exit after the run function has returned. This permits Qt to optimize for more speed and less flicker than a call to repaint() does. If you launch a long-running task in this thread, then your GUI will freeze until the task terminates. – QCoreApplication::exec: The event loop is already running. Tkinter is not thread-safe, and it requires that all GUI updates be performed in the main thread. However, a QThread's start() function executes its run() method in the thread after the thread is initialized so a subclass of QThread should be created and its run method should run LoadThread. Please visit https://discuss. use('Agg') 加这个是有效的，但一定要加载代码的主函数里，否则仍然可能会报错。比如加载train. It is important to remember that a QThread instance lives in the old thread that instantiated it, not in the new thread that calls run(). There is only one running event loop per application. It is necessary to call this function to start event handling. Just check an internal flag within the loop that is run within the thread. It's the event loop of the program. moveToThread() and QThread objects to create worker threads. As @jsulm has said, if you want something to happen call from inside the main loop you need to use async calls on the serial port. To arrange for the GLib main loop to be the default, use: Sep 7, 2014 · Use QThread to create loop what your want. When the event loop stops running, exec_() returns, allowing sys. Jun 9, 2013 · I have a simple PyQt application, which has a tray icon and can be hidden from taskbar by clicking close button or tray icon. Section 6. We’ll develop a simple text editor program. UR的出不克: 感谢，终于破案了. 后来才弄懂一个程序里只能有一个app，于是乎，我将PersonalInfo类里的app = QtWidgets. Nov 5, 2015 · The exec() method "Enters the main event loop and waits until exit() is called" : the script will be blocked on the line app. If flags are specified, only events of the types allowed by the flags will be processed. exec_()) is executed. Possibly by moving your current main thread code into a worker thread. Dec 23, 2022 · if the logic is more complicated you can use signals to communicate back to the main thread to do the GUI updates Updating GUI elements in MultiThreaded PyQT, but you must not update the GUI from a child thread. """ QApplication. Sep 28, 2018 · I have a for loop in a QThread, which is started from the main GUI via a push button. You can also unsafely do so, using threding. 要解决Tkinter RuntimeError主线程不在主循环中的错误，我们可以采取以下方法： May 21, 2019 · In this tutorial we'll learn how to use PyQt to create desktop applications with Python. PyQt’s Layout Managers provide us with a productive way of arranging PyQt Widgets on a GUI. When the for loop is over I would like to come back to the main thread (which is inside the Gui class) and do something else. It checks the event queue continuously and forwards the events to their handlers. Use threads and processes. Now I want to exit the main loop, do something else and restart the main loop with a different html form later. Main Window, Menus, Toolbars, and Status Bars # This section shows you how to create the main window and other commonly used widgets like menu bars, toolbars, and status bars. Calling any of them just tells the event loop of that thread to exit. Apr 18, 2021 · I am new to asyncio and I want to leverage it for my pyqt application to handle communication over a tcp connection. To achieve this we will employ the QThread class, that provides a cross-platform API to work with threads. app. exec_()) would cause the script to end when the window is closed. I am on a Xubuntu 12. Hello, I am currently starting to use PyQt5 and created my first GUI. If you want to do repetitive operations, use QTimer, if you need to communicate with external sources (eg: network replies), use QThread or the appropriate Oct 18, 2020 · The windows run normally when they are not contained within a loop, and they also run pretty well in the first iteration of the loop. argv)和sys. When Button 'start' is pressed execute 'function' n-times until Button 'stop' is pressed (imagine a stopwatch) if I press Button 'start' again 'function' gets once again executed and so on. After user clicks " Sep 7, 2014 · Use QThread to create loop what your want. exit(): "Tells the thread's event loop to exit with a return code. exec_() call basically starts 'a while loop that handles [QT] signals' etc. Pyqt / Pyside: thread-safe callbacks + main loop integration (Python recipe) by Justin Israel Forked from Recipe 578299 (A modified version that removes the seemingly unnecessary dispatching thread and queue, and replaces it with a simple function that wraps and posts the callback event. . Please visit https://bugs. KDE is an international community creating free and open source software. The main loop detects various events and sends them to the event object. 04 box with PyQt4, Python 2. execute slots in response to signals raised, or raise signals which other Feb 5, 2013 · I believe this is exactly what you're seeing: your Tkinter code in Thread-1 is trying to peek into the main thread to find the main loop, and it's not there. Application can be closed from tray icon context menu. PyQt是一个用于图形用户界面(GUI)小工具的工具包。它是从Qt的库中提取的。PyQt是Python语言和Qt库结合的产物。PyQt是与Qt Builder一起出现的。我们将用它来从Qt Creator中获取Python代码。在Qt设计器的支持下，我们可以建立一个GUI，然后我们可以为这个GUI获得python Mar 27, 2023 · RuntimeError: main thread is not in main loop occurs when you try to update your Tkinter GUI from a different thread other than the main thread. exec() , you get the window to e. The event loop waits for an event to occur and then dispatches it to perform some task. Avoid launching long-running tasks in the main thread of a PyQt application. exec() to start the event loop. It's a loop that waits for any event (usually user events, but also timed or system events), and, after processing the first available event, it starts again (hence, loop) waiting for more events in the queue; if there are more queued events waiting, they will be processed (usually in their insertion order), otherwise it Apr 20, 2025 · The state is being changed from outside your event loop. Does anyone know how to achieve this as simple as possible? I am new to Scrapy / PyQt / Multiprocessing / Twisted. The QApplication. Aug 28, 2020 · @Sherafati "An EVENT loop is a loop of EVENTS(signals)": not exactly. NB: using sys. Sep 7, 2012 · I have a PyQt4 class that displays a html form and fetches the input, thanks to previous questions here (an older one is here). RuntimeError: main thread is not in main loop. There are two main approaches to running independent tasks within a PyQt application: May 22, 2020 · The function of app. Visit our main page to know more: https://kde. qt. The better we lay out our Widgets, the more polished and professional our GUI application can look. reenter_qt, self. An alternative is to use a QTimer to send a signal at regular intervals to do the polling. – xioxox Jun 9, 2013 · I have a simple PyQt application, which has a tray icon and can be hidden from taskbar by clicking close button or tray icon. If you are new to PyQt, I recommend this book. g. Use queue. 2546. Jul 22, 2011 · I have a program which interfaces with a radio I am using via a gui I wrote in PyQt. As for the loop, I don't think you are showing the code that cause the problem. kde. But your long_task function is blocking the event loop to process any event (including exiting) or be aware of its conclusion. After user clicks " Jul 21, 2016 · Currently, the only main loop supported by dbus-python is GLib. so in the main python program i have a pseudo "do while" loop (while True: and break with a condition) to read on serial port the data provided by the reader. If you take a step back and think about what you want to happen in your application, then you can probably sum it up with "stuff to happen at the same time as other stuff happens". Use QMainWindow to create the main window for the PyQt application and call the show() method to display the window on the screen. So for example you could create and show a window, and then add other widgets to it from within the python shell whilst the window is still visible. Generally speaking, no user interaction can take place before calling . QApplication The QApplication class manages the control flow and major settings of GUI applications. Obviously one of the main functions of the radio is to transmit data, but to do this continuously, I have to loop the writes, which causes the gui to hang. 解决方法. 在本文中，我们将介绍如何在PyQt中执行Python代码，并将重点放在从PyQt事件循环中执行代码上。PyQt是一个用于开发GUI应用程序的Python库，它提供了丰富的功能和灵活的界面设计选项。 Jun 9, 2015 · This function does not cause an immediate repaint; instead it schedules a paint event for processing when Qt returns to the main event loop. Call the app. Jul 17, 2020 · First of all, GUI elements should always be created and accessed from the main Qt thread, no from another one. As a special case, modal widgets like QMessageBox can be used before calling exec(), because modal widgets use their own local event loop. PyQt：在GUI中运行循环 在本文中，我们将介绍如何在PyQt中运行一个循环。 PyQt是一个用于创建GUI（图形用户界面）应用程序的Python库，它基于Qt框架。 在GUI程序中经常需要使用循环来处理用户输入、更新界面等操作，但是如果循环阻塞了GUI线程，就会导致应用 Jun 20, 2022 · Finally, we execute the application via app. org ----- This is not a technical support forum. exit(app. thread and by optionally suppressing potential warning issues. PyQt 从PyQt事件循环中执行Python代码. As a special case, modal widgets like QMessageBox can be used before calling , because modal widgets use their own local event loop. Example of QTimer usage: in main() before exec_(): An event loop manages all events of the PyQt application. Besides that, you are already using a QTimer, using another loop is completely unnecessary, at least for the given example. io: QApplication Class: The QApplication class manages the GUI application's control flow and main settings. The event handler deals with the event, then passes control back to the event loop to wait for more events. 0. Returns the value that was passed to exit() . The main event loop receives events from the window system and dispatches these to the application widgets. But, when the repeat condition is satisfied, even though the loop does iterate (prints 'test' again) - the ui and ui2 windows do not get displayed again, and subsequently the program hits the exit condition and Jan 3, 2023 · RuntimeError: main thread is not in main loop. In most cases, this means keeping all GUI code within the main body of your script, and not inside functions or methods that are called from other threads. Your can find example in here , here and a lot of in google search result. When we call the exec_() method of the application, the application enters the main loop. exec_() enters this loop, which is why you don't see the code following that execute. sleep(msec)を使ったら、GUIがフリーズすることがわかりました。 QT Aug 21, 2021 · Since Qt's main loop runs in our application's main thread, and our task runs in a secondary thread, the user interface remains active while the file is downloaded in the background. exec ()) Layout Managers. a looping function can re-emit itself to allow the GUI to update itself before calling this function again. 目前，dbus-python 唯一支持的 main loop 是 GLib 。 dbus-python has a global default main loop, which is the easiest way to use this functionality. There will not be any event loop running in the thread unless you call exec(). It is called by Trio at the end of an event loop run in order to relinquish back to Qt's event loop. ). Thanks in advance. py主函数里 Nov 18, 2018 · 測定して10秒休み、また同じ測定をする、というプログラムをPyQt5で作っています。 最初休むのにtime. Jan 8, 2016 · The function connected to the started signal will run the thread which it was connected, the main GUI thread. The thread which runs this event loop — commonly referred to as the GUI thread — also handles all window communication with the host operating system. QMainWindow – show you how to create the main window that supports the menu bars, toolbars, and status bars. Use QObject. During that time, the user won’t be able to interact with the application, resulting in a bad user experience. Or what can be problem, ple Dec 10, 2022 · It's not the window blocking, it's the application event loop, which is essential for almost any UI based toolkit to let it process user and system events (user input, window drawing, etc). org for user support. exec_() is to run the main loop, which must be called to start the event processing, and the method is called to enter the main loop of the program until the exit() is called. Jun 12, 2020 · In Qt, whether C++/Python/PyQt5/PySide2, you need to spin the main event loop via QApplication::exec() to have a proper running application. Since it's till part of the main loop, other threads closing shouldn't affect it at all. QApplication(sys. Feb 15, 2023 · You do not put a qDebug() into the main loop, you have put it after the main loop. exec_() until the window is closed. Oct 20, 2021 · In the event loop, the queue is checked on each iteration and if a waiting event is found, the event and control is passed to the specific event handler for the event. PyQt. ". You shouldn't need your own loop to do that stuff. org to report bugs. Manager for handling shared data between them. ----- This is not a bug tracker. exec_() on your QApplication object and runs within the same thread as your Python code. Enters the main event loop and waits until exit() is called. I made this trivial demo to learn how to deal with the QT loop in asyncio contex Dec 21, 2024 · Python PyQt Basic: Exercise-1 with Solution. PyQt graphical user interface (GUI) applications have a main thread of execution that runs the event loop and GUI. Sep 22, 2010 · The app. 7 and Scrapy 0. First we'll create a series of simple windows on your desktop to ensure that PyQt is working and introduce some of the basic concepts. From doc. Application events are generated primarily from users, but they can also be generated by other means, such as an Internet connection, a window manager, or a timer. exec_()) to finally run, and this exits the program. Now I would like a program that does the following. Use QThreadPool and QRunnable if you need to manage a pool of worker threads. exec_())注释掉，运行，发现还是不行，曾一度有手动敲代码实现界面的冲动… Pyqt / Pyside: thread-safe global queue + main loop integration (Python recipe) by Esteban Castro Borsani Apr 28, 2023 · Ensure that all Tkinter-related tasks (e. Queue to pass tasks to the main thread: Events are handled by an event loop, also known as a main loop. Apr 15, 2015 · Then, i want to hide it and show the second MainWindow when the RFID Reader (who's working on "auto-reading mode") read an RFID Tag. Oct 31, 2018 · 一、将两个类写入到一个Python文件夹中 使用Qtdesigner设计ui界面，实行界面分离，分别设计两个界面，一个是登录的界面，一个是主界面 然后新建一个Python文件，在文件中分别将这两个界面UI引入，分别创建两个类，一个是实现登录显示的类，另一个是实现主界面显示的类。 Sep 30, 2022 · You can safely create an instance of QApplication outside your "main"-loop (as a different process) using multiprocessing, plus multiprocessing. and the window is also active, I can play with the window, Show me how your way, with no app. QThread i subclass in QObject so your can connect just like QWidget old-style or new-style signal. Only after you have closed all qt windows will anything remaining be executed. exec_() runs an event loop until all the windows are closed. Generally speaking, no user interaction can take place before calling exec(). By posting an event on the Qt event loop that contains Trio's next entry point, it ensures that Trio's event loop will be scheduled again by Qt. postEvent (self. You shouldn't even need to use the other Thread classes to do this, it's even bad to call GUI events from threads, it can lead to crashes. As far as I understood, one should use the join method to wait for the thread to be finished. Calling update() several times normally results in just one paintEvent() call. load, the function you want to execute. 薏米薏米: import matplotlib matplotlib. So, here are some options: Do what the Tkinter docs recommend and use TkInter from the main thread. Feb 24, 2013 · I would like to have a non blocking ui, though I want to integrate the Twisted event loop in the PyQt main loop. Feb 15, 2023 · The main loop is inside the QApplication::exec(), and that does not return till told to quit. , creating, updating, or destroying widgets) are performed in the main thread of your application. – Jan 21, 2015 · When you use PyQt/PySide in an interactive session, the event processing is set up automatically in the background in a way that allows you to interact directly with the objects. 主循环（main loop）是Tkinter应用程序的核心。它是一个无限循环，用于监听用户输入并更新应用程序的界面。通过调用mainloop()方法，我们可以将主循环启动起来。 2. Sep 17, 2023 · 最后，解决"main thread is not in main loop"问题需要仔细分析代码，确保所有的线程和进程都正确地在主循环中运行，并且使用适当的同步机制来保证程序的正确性。 ### 回答3： 解决 "main thread is not in main loop" 的问题的方法取决于出现此错误的具体情况。 Aug 1, 2014 · pyqt comes with its own (infinite) event loop so that you don't have to build your own. Apr 15, 2017 · The event loop is started by calling . If you do, you're talking about multiple threads and you need to look at the docs for QThread and/or QEventLoop. Write a Python program to create a blank window using PyQt. I probably missing something obvious. The main loop is inside the QApplication::exec() , and that does not return till told to quit. 12. An event loop is an infinite loop in which all events from the user, the window system, and any other sources are processed and dispatched. 本文详细介绍使用PyQt5进行GUI界面设计时，如何实现多界面间的跳转，包括两个界面的基本跳转方法及三个以上界面的嵌套跳转技巧。 摘要生成于 C知道 ，由 DeepSeek-R1 满血版支持， 前往体验 > 最近使用 pyqt5 做GUI界面，拖拽控件可以将界面设计得很漂亮，但是不会多界面之间的跳转，比如点击一个button就进入第二个界面，第一个界面关闭，关闭第二个界面又进入主界面，如果看到这里你心里正想：对！ 这就是我想知道的！ 看完这篇博客就会明白如何实现，本博客将介绍上述功能的实现方法以及本人的走坑史~ 首先是两个界面的实现，我使用拖拽控件实现的，下面是两个界面截图，分别为主界面和子界面： Aug 21, 2021 · Since Qt's main loop runs in our application's main thread, and our task runs in a secondary thread, the user interface remains active while the file is downloaded in the background. Then we'll take a brief look at the event loop and how it relates to GUI programming in Python. – xioxox close() does not just close the screen, it quits the program. exec(), and run the application's main loop until the user closes it: sys. Apr 16, 2021 · 一、问题 在训练过程中，训练了几个epoch，后出现"RuntimeError: main thread is not in main loop"问题； 二、问题分析 在多卡训练的时候和某个子线程冲突，大概率是因为每个epoch结束都使用了matplotlib和sns等作图工具包, 相当于进入了另一个线程之中。 Feb 4, 2010 · Can I debug PyQt application when is main loop running ? Pdb, NetBeans, PyDev, all "freeze" when sys. ohpy fkndo asvztb ukaq anoza dvdw snoif eihn totso vrsek nydc mfgfe ahnifkj qkwgc jsmi