如何使用 Qthread 通过 PyQt 更新 Matplotlib 图？

Question

我真的很难理解如何在 PyQt 中使用线程。我做了一个简单的例子来说明我想在用户界面中做什么。在下面的代码中，我希望用户输入股票行情（例如，您可以输入“bby”、“goog”或“v”）并绘制特定时期内股票的价值。问题是在更复杂的用户界面中，或者在很长一段时间内，用户界面在绘图更新时冻结。所以我制作了一个“绘图仪”类，当它收到某个信号时更新绘图（覆盖 Qthread.run 显然不是你做错的正确方法）。我想让这个“绘图仪”在主线程之外的另一个线程中运行。

一旦我取消注释线程，程序就会停止工作。我尝试移动新线程的启动以及“连接”，但没有任何效果。我认为即使在阅读了文档并查看了 Qt 网站上的示例之后，我仍然不太理解 Qthread 的工作原理。

如果您知道如何做到这一点，那将会有很大帮助！（我正在使用 Python 3.5 和 PyQt5）

from PyQt5.QtCore import *
from PyQt5.QtWidgets import *
from matplotlib.axes._subplots import Axes
from matplotlib.figure import Figure
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
import sys
from datetime import datetime, timedelta
import time
import quandl


class MyMplCanvas(FigureCanvas):
    """Ultimately, this is a QWidget (as well as a FigureCanvasAgg, etc.)."""
    send_fig = pyqtSignal(Axes, str, name="send_fig")

    def __init__(self, parent=None):
        self.fig = Figure()
        self.axes = self.fig.add_subplot(111)

        # We want the axes cleared every time plot() is called
        self.axes.hold(False)

        FigureCanvas.__init__(self, self.fig)
        self.setParent(parent)

        FigureCanvas.setSizePolicy(self, QSizePolicy.Expanding, QSizePolicy.Expanding)
        FigureCanvas.updateGeometry(self)

    def update_plot(self, axes):
        self.axes = axes
        self.draw()

class MainWindow(QMainWindow):
    send_fig = pyqtSignal(Axes, str, name="send_fig")

    def __init__(self):
        super().__init__()

        self.main_widget = QWidget(self)
        self.myplot = MyMplCanvas(self.main_widget)
        self.editor = QLineEdit()
        self.display = QLabel("Vide")

        self.layout = QGridLayout(self.main_widget)
        self.layout.addWidget(self.editor)
        self.layout.addWidget(self.display)
        self.layout.addWidget(self.myplot)

        self.main_widget.setFocus()
        self.setCentralWidget(self.main_widget)

        self.move(500, 500)
        self.show()

        self.editor.returnPressed.connect(self.updatePlot)

        self.plotter = Plotter()
        self.send_fig.connect(self.plotter.replot)

        self.plotter.return_fig.connect(self.myplot.update_plot)


    def updatePlot(self):
        ticker = self.editor.text()
        self.editor.clear()
        self.display.setText(ticker)

        # thread = QThread()
        # self.plotter.moveToThread(thread)

        self.send_fig.emit(self.myplot.axes, ticker)

        # thread.start()


class Plotter(QObject):
    return_fig = pyqtSignal(Axes)

    @pyqtSlot(Axes, str)
    def replot(self, axes, ticker):  # A slot takes no params
        print(ticker)
        d = datetime.today() - timedelta(weeks=52)  # data from 1week ago
        data = quandl.get("YAHOO/"+ticker+".6", start_date=d.strftime("%d-%m-%Y"), end_date=time.strftime("%d-%m-%Y"))
        axes.plot(data)
        self.return_fig.emit(axes)


if __name__ == '__main__':
    app = QApplication(sys.argv)
    win = MainWindow()
    sys.exit(app.exec_())

Answer 1

thread第一个问题是，一旦启动，您就会丢失对其的引用。要保留引用，请使用类变量，即self.thread代替thread.

接下来，在执行任何操作之前必须启动线程。所以需要放在self.thread.start()信号发射前面。

现在，它已经可以工作了，但是一旦您想要启动一个新线程，就会出现下一个问题。所以，你需要先杀死旧的。由于旧的绘图仪Plotter将无家可归，因此解决方案是在每次想要绘图时创建一个新的绘图仪以及一个新的线程。这就是下面的解决方案的工作方式。
或者，您也可以始终使用相同的绘图仪和线程。唯一要记住的是，总是只有一个工人（绘图员）和一个线程，如果删除其中一个，另一个就会难过。

为了测试它，我需要更改一些小东西，例如使用 PyQt4 而不是 5 并替换数据生成。这是工作代码。

from PyQt4.QtCore import *
from PyQt4.QtGui import *
from matplotlib.axes._subplots import Axes
from matplotlib.figure import Figure
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
import sys
from datetime import datetime, timedelta
import numpy as np



class MyMplCanvas(FigureCanvas):
    """Ultimately, this is a QWidget (as well as a FigureCanvasAgg, etc.)."""
    send_fig = pyqtSignal(Axes, str, name="send_fig")

    def __init__(self, parent=None):
        self.fig = Figure()
        self.axes = self.fig.add_subplot(111)

        # We want the axes cleared every time plot() is called
        self.axes.hold(False)

        FigureCanvas.__init__(self, self.fig)
        self.setParent(parent)

        FigureCanvas.setSizePolicy(self, QSizePolicy.Expanding, QSizePolicy.Expanding)
        FigureCanvas.updateGeometry(self)

    def update_plot(self, axes):
        self.axes = axes
        self.draw()

class MainWindow(QMainWindow):
    send_fig = pyqtSignal(Axes, str, name="send_fig")

    def __init__(self):
        super(MainWindow, self).__init__()

        self.main_widget = QWidget(self)
        self.myplot = MyMplCanvas(self.main_widget)
        self.editor = QLineEdit()
        self.display = QLabel("Vide")

        self.layout = QGridLayout(self.main_widget)
        self.layout.addWidget(self.editor)
        self.layout.addWidget(self.display)
        self.layout.addWidget(self.myplot)

        self.main_widget.setFocus()
        self.setCentralWidget(self.main_widget)

        self.move(500, 500)
        self.show()

        self.editor.returnPressed.connect(self.updatePlot)

        # plotter and thread are none at the beginning
        self.plotter = None 
        self.thread = None



    def updatePlot(self):
        ticker = self.editor.text()
        self.editor.clear()
        self.display.setText(ticker)

        # if there is already a thread running, kill it first
        if self.thread != None and self.thread.isRunning():
            self.thread.terminate()

        # initialize plotter and thread
        # since each plotter needs its own thread
        self.plotter = Plotter()
        self.thread = QThread()
        # connect signals
        self.send_fig.connect(self.plotter.replot)
        self.plotter.return_fig.connect(self.myplot.update_plot)
        #move to thread and start
        self.plotter.moveToThread(self.thread)
        self.thread.start()
        # start the plotting
        self.send_fig.emit(self.myplot.axes, ticker)



class Plotter(QObject):
    return_fig = pyqtSignal(Axes)

    @pyqtSlot(Axes, str)
    def replot(self, axes, ticker):  # A slot takes no params
        print(ticker)
        d = datetime.today() - timedelta(weeks=52)  # data from 1week ago
        # do some random task
        data = np.random.rand(10000,10000)
        axes.plot(data.mean(axis=1))
        self.return_fig.emit(axes)


if __name__ == '__main__':
    app = QApplication(sys.argv)
    win = MainWindow()
    sys.exit(app.exec_())

这是提到的第二个选项的解决方案，即创建一个工作线程和一个线程，并在整个程序运行时使用它们。

from PyQt4.QtCore import *
from PyQt4.QtGui import *
from matplotlib.figure import Figure
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
import sys
import numpy as np



class MyMplCanvas(FigureCanvas):

    def __init__(self, parent=None):
        self.fig = Figure()
        self.axes = self.fig.add_subplot(111)
        # plot empty line 
        self.line, = self.axes.plot([],[], color="orange")

        FigureCanvas.__init__(self, self.fig)
        self.setParent(parent)

        FigureCanvas.setSizePolicy(self, QSizePolicy.Expanding, QSizePolicy.Expanding)
        FigureCanvas.updateGeometry(self)


class MainWindow(QMainWindow):
    send_fig = pyqtSignal(str)

    def __init__(self):
        super(MainWindow, self).__init__()

        self.main_widget = QWidget(self)
        self.myplot = MyMplCanvas(self.main_widget)
        self.editor = QLineEdit()
        self.display = QLabel("Vide")

        self.layout = QGridLayout(self.main_widget)
        self.layout.addWidget(self.editor)
        self.layout.addWidget(self.display)
        self.layout.addWidget(self.myplot)

        self.main_widget.setFocus()
        self.setCentralWidget(self.main_widget)
        self.show()

        # plotter and thread are none at the beginning
        self.plotter = Plotter()
        self.thread = QThread()

        # connect signals
        self.editor.returnPressed.connect(self.start_update)
        self.send_fig.connect(self.plotter.replot)
        self.plotter.return_fig.connect(self.plot)
        #move to thread and start
        self.plotter.moveToThread(self.thread)
        self.thread.start()

    def start_update(self):
        ticker = self.editor.text()
        self.editor.clear()
        self.display.setText(ticker)
        # start the plotting
        self.send_fig.emit(ticker)


    # Slot receives data and plots it
    def plot(self, data):
        # plot data
        self.myplot.line.set_data([np.arange(len(data)), data])
        # adjust axes
        self.myplot.axes.set_xlim([0,len(data) ])
        self.myplot.axes.set_ylim([ data.min(),data.max() ])
        self.myplot.draw()


class Plotter(QObject):
    return_fig = pyqtSignal(object)

    @pyqtSlot(str)
    def replot(self, ticker):
        print(ticker)
        # do some random task
        data = np.random.rand(10000,10000)
        data = data.mean(axis=1)
        self.return_fig.emit(data)


if __name__ == '__main__':
    app = QApplication(sys.argv)
    win = MainWindow()
    sys.exit(app.exec_())