在 PyQt5 中显示带布局和不带布局的小部件

在一个窗口的“tab1”选项卡上，应显示来自网络摄像头的视频图像和图表，按下按钮时会更新该图表。窗口的大小、小部件以及窗口上的位置必须是固定的。我设法将图形和视频图像放置在“QHBoxLayout()”上。但是，当固定放置在“MyWidget”类中的“tab1”选项卡上（设置小部件的位置和大小时），而不是“MainWindow”上时，它们不会显示。我为什么要这样做 - 最后，我的图表应该从表格中获取值，并在我单击表格单元格时进行更新，并且这已经在“MyWidget”类中实现了。 1 个带有“QHBoxLayout()”的布局选项（工作）：

import numpy as np
import sys    
from PyQt5.Qt import *    
import random    
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure
import matplotlib.pyplot as plt
class MyWidget(QWidget):
    def __init__(self, parent):
        global kolichestvo_tochek
        global y
        super(QWidget, self).__init__(parent)    
        self.tabs = QTabWidget()
        self.tab1 = QWidget()
        self.layout_1 = QHBoxLayout()                
        self.tab1.setLayout(self.layout_1)
        self.tabs.addTab(self.tab1, 'tab1')
        # График
        self.figure = Figure()
        self.canvas = FigureCanvas(self.figure)
        self.ax = self.figure.add_subplot(111)
        self.layout_1.addWidget(self.canvas)            
        self.update()
        self.layout = QVBoxLayout(self)
        self.layout.addWidget(self.tabs)
        self.sc = MplCanvas(self, width=5, height=4, dpi=100)
        # Камера
        self.viewfinder = QCameraViewfinder()
        self.cameraInfo = QCameraInfo.defaultCamera()
        self.camera = QCamera(self.cameraInfo)
        self.camera.setViewfinder(self.viewfinder)    
        self.layout_1.insertWidget(0, self.viewfinder)
        if self.camera.status() != QCamera.UnavailableStatus:
            self.camera.start()
    # Реакция на нажатие Enter на нампаде! клавиатуры
    def keyPressEvent(self, e):
        k = e.key()
        if k == 16777221:
            super().keyPressEvent(e)
            self.update()        
    def update(self):                        
        global y
        self.ax.clear()
        x = np.arange(1, 6)
        y = np.random.randint(1, 10, size=5)
        self.ax.plot(x, y)            
        self.canvas.draw()    
class MainWindow(QMainWindow):
    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)            
        self.resize(1500, 470)
        self.widget1 = MyWidget(self)                        
        self.central_widget = QWidget()
        self.setCentralWidget(self.central_widget)
        main_layout = QVBoxLayout(self.central_widget)
        main_layout.addWidget(self.widget1)
class MplCanvas(FigureCanvas):
    def __init__(self, parent=None, width=5, height=4, dpi=100):
        fig = Figure(figsize=(width, height), dpi=dpi)
        self.axes = fig.add_subplot(111)
        super(MplCanvas, self).__init__(fig)
if __name__ == '__main__':
    app = QApplication(sys.argv)
    app.setApplicationName("WebCam")
    window = MainWindow()
    window.show()
    sys.exit(app.exec())

2 没有“布局”的选项（不起作用）：

import numpy as np
import sys    
from PyQt5.Qt import *    
import random
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure
import matplotlib.pyplot as plt
class MyWidget(QWidget):
    def __init__(self, parent):
        global kolichestvo_tochek
        global y
        super(QWidget, self).__init__(parent)    
        self.tabs = QTabWidget()
        self.tab1 = QWidget(self)
        # График
        self.figure = Figure()
        self.canvas = FigureCanvas(self.figure)
        self.ax = self.figure.add_subplot(111)    
        self.update()
        self.layout = QVBoxLayout(self)
        self.sc = MplCanvas(self, width=5, height=4, dpi=100)
        # Камера
        self.viewfinder = QCameraViewfinder()
        self.cameraInfo = QCameraInfo.defaultCamera()
        self.camera = QCamera(self.cameraInfo)
        self.camera.setViewfinder(self.viewfinder)
        if self.camera.status() != QCamera.UnavailableStatus:
            self.camera.start()    
    # Реакция на нажатие Enter на нампаде! клавиатуры
    def keyPressEvent(self, e):
        k = e.key()
        if k == 16777221:
            super().keyPressEvent(e)
            self.update()        
    def update(self):                        
        global y
        self.ax.clear()
        x = np.arange(1, 6)
        y = np.random.randint(1, 10, size=5)
        self.ax.plot(x, y)            
        self.canvas.draw()
class MainWindow(QMainWindow):        
    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)            
        self.resize(1500, 470)            
        self.widget1 = MyWidget(self)                        
        self.central_widget = QWidget()
        self.setCentralWidget(self.central_widget)
        central_widget = QTabWidget()            
        central_widget.addTab(self.widget1, "tab1")
        self.setCentralWidget(central_widget)
        
class MplCanvas(FigureCanvas):
    def __init__(self, parent=None, width=5, height=4, dpi=100):
        fig = Figure(figsize=(width, height), dpi=dpi)
        self.axes = fig.add_subplot(111)
        super(MplCanvas, self).__init__(fig)        
        
if __name__ == '__main__':
    app = QApplication(sys.argv)
    app.setApplicationName("WebCam")
    window = MainWindow()
    window.show()
    sys.exit(app.exec())