pyqt5运行后非正常退出

Question

写了一个pyqt5的界面
代码如下：

import sys
import mainui
from PyQt5.QtWidgets import QApplication, QMainWindow, QFileDialog

# import os
# os.environ["CUDA_VISIBLE_DEVICES"]="-1"

class MainCode(QMainWindow, mainui.Ui_MainWindow):

    def __init__(self):
        QMainWindow.__init__(self)
        mainui.Ui_MainWindow.__init__(self)
        self.setupUi(self)
        self.pushButton.clicked.connect(self.on_save)
        self.pushButton_2.clicked.connect(self.on_open)

    def on_save(self):
        FullFileName, _ = QFileDialog.getSaveFileName(self, '文件另存为', r'./', 'TXT (*.txt)')
        set_text = self.txt_view.toPlainText()
        with open(FullFileName, 'wt') as fp:
            print(set_text, file=fp)

    def on_open(self):
        txtstr = ""
        FullFileName, _ = QFileDialog.getOpenFileName(self, '打开', r'./', 'TXT (*.txt)')
        with open(FullFileName, 'rt') as fp:
            lines = fp.readlines()
            for line in lines:
                txtstr = txtstr + line
        self.txt_view.setText(txtstr)



if __name__ == '__main__':
    app = QApplication(sys.argv)
    ui=MainCode()
    # ui.setupUi(mainwindows)
    # ui.setupUi(ui)
    ui.show()
    sys.exit(app.exec())

ui文件代码如下：

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'mainui.ui'
#
# Created by: PyQt5 UI code generator 5.15.4
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.


from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(800, 600)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.label = QtWidgets.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(10, 10, 121, 31))
        self.label.setObjectName("label")
        self.widget = QtWidgets.QWidget(self.centralwidget)
        self.widget.setGeometry(QtCore.QRect(10, 50, 771, 501))
        self.widget.setObjectName("widget")
        self.verticalLayout = QtWidgets.QVBoxLayout(self.widget)
        self.verticalLayout.setContentsMargins(0, 0, 0, 0)
        self.verticalLayout.setObjectName("verticalLayout")
        self.textBrowser = QtWidgets.QTextBrowser(self.widget)
        self.textBrowser.setObjectName("textBrowser")
        self.verticalLayout.addWidget(self.textBrowser)
        self.horizontalLayout = QtWidgets.QHBoxLayout()
        self.horizontalLayout.setObjectName("horizontalLayout")
        self.pushButton = QtWidgets.QPushButton(self.widget)
        self.pushButton.setObjectName("pushButton")
        self.horizontalLayout.addWidget(self.pushButton)
        self.pushButton_2 = QtWidgets.QPushButton(self.widget)
        self.pushButton_2.setObjectName("pushButton_2")
        self.horizontalLayout.addWidget(self.pushButton_2)
        self.verticalLayout.addLayout(self.horizontalLayout)
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 800, 23))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.label.setText(_translate("MainWindow", "请在此输入："))
        self.pushButton.setText(_translate("MainWindow", "保存文件"))
        self.pushButton_2.setText(_translate("MainWindow", "选择文件"))

程序运行后，点击任意一个按钮后直接卡死
且文本框无法输入文本，这是为什么呢？
响应结果如下：

进程已结束,退出代码-1073740791 (0xC0000409)

Answer 1

本地试了一下，至少有两个问题
1、MainCode没有txt_view属性
2、保存和打开文件，点击弹出窗口取消键时，返回FullFileName为空，不应执行后续部分