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已删除QWidget类型的包装的c/c++对象

pyqt5 pyqt python

Nimish Bansal · 技术社区 · 7 年前

class window25(QtWidgets.QMainWindow):
    def __init__(self):
        try:
            super(window25,self).__init__()
            self.lineedit=QtWidgets.QLineEdit()
            self.checkbox=QtWidgets.QCheckBox()
            self.optBox=QtWidgets.QRadioButton()
            self.btn=QtWidgets.QPushButton("press me")
            self.guichange()
            self.btn.clicked.connect(self.guichange)
            self.show()
        except Exception as E:
            print(E)
    def guichange(self):
        try:
            wid=QtWidgets.QWidget()
    #        self.setCentralWidget()
            myLayout=QtWidgets.QVBoxLayout()
            myLayout.addWidget(self.btn)
            myLayout.addWidget(random.choice([self.lineedit,self.checkbox,self.optBox]))
            wid.setLayout(myLayout)    
            self.setCentralWidget(wid)
        except Exception as E:
            print(E)


app=QtWidgets.QApplication([])
ex=window25()
sys.exit(app.exec_())

我正试图做这个实验。虽然我知道QStackedWidget可以更改窗口,但我尝试了其他方法,即按下按钮随机更改主窗口中心小部件。几次成功后(即按下按钮3,4次可正常工作),但之后我出现了一个错误

已删除QCheckBox类型的包装的c/c++对象

已删除QLineEdit类型的包装的c/c++对象

我无法理解是哪个陈述导致了这个错误,以及我错在哪里或为什么错

1 回复 | 直到 7 年前

Community Mohan Dere 5 年前

这是由Qt的实现和原理引起的,回顾 documentation 观察:

[...]

QObject在对象树中组织自己。当您创建 QObject与另一个对象作为父对象时,该对象将自动将其自身添加到父级的子级()列表中。父母拥有所有权对象的名称;i、例如,它将在其析构函数。可以按名称和可选类型查找对象使用findChild()或findChildren()。

[...]

正如他所说,如果父母也毁灭了孩子,而且由于所有的小部件都 QObject 作为其前身,他们也遵守这些规则。

但是为什么一些小部件被破坏了呢?

每次使用 setCentralWidget() 以前是中心小部件的对象将被删除。

CentralWidget()的子级是什么?

当小部件附加到布局时,这些小部件被设置为使用该布局的小部件的父级。

wid = QtWidgets.QWidget()   
myLayout.addWidget(tmp)    
wid.setLayout(myLayout)    
self.setCentralWidget(wid)

为什么不消除QPushButton?

发生了什么 QPushButton 有时在使用其他小部件之前 setCentralWidget() ,即删除父级,它将从父级更改为:

myLayout=QtWidgets.QVBoxLayout() # some parent
myLayout.addWidget(self.btn)     # a new parent is established
[...]
self.setCentralWidget(wid)       # elimination of the old parent

最后,我将使用以下代码解释一个随机示例:

class window25(QtWidgets.QMainWindow):
    counter = 0
    def __init__(self):
        try:
            super(window25,self).__init__()
            self.lineedit=QtWidgets.QLineEdit()
            self.lineedit.setObjectName("QLineEdit")
            self.checkbox=QtWidgets.QCheckBox()
            self.checkbox.setObjectName("QCheckBox")
            self.optBox=QtWidgets.QRadioButton()
            self.optBox.setObjectName("QRadioButton")
            self.btn=QtWidgets.QPushButton("press me")
            self.guichange()
            self.btn.clicked.connect(self.guichange)
            self.show()
        except Exception as E:
            print(E)
    def guichange(self):
        try:
            print("\ncall guichange")
            wid = QtWidgets.QWidget()
            wid.setObjectName("wid-{}".format(self.counter))
            myLayout=QtWidgets.QVBoxLayout()
            myLayout.addWidget(self.btn)
            tmp = random.choice([self.lineedit,self.checkbox,self.optBox])
            myLayout.addWidget(tmp)
            wid.setLayout(myLayout)    
            wid.destroyed.connect(lambda obj: print("delete: ",obj.objectName()))
            tmp.destroyed.connect(lambda obj: print("delete: ",obj.objectName()))
            self.setCentralWidget(wid)
            print("add: {} parent: {}".format(tmp.objectName(),tmp.parent().objectName()))
            self.counter += 1

        except Exception as E:
            print(E)

说明:

call guichange
QLineEdit                      # tmp is QLineEdit
add: QLineEdit parent: wid-0   # set to wid-0 as the parent of QLineEdit

call guichange
QLineEdit                      # tmp is QLineEdit
add: QLineEdit parent: wid-1   # set to wid-1 as new parent of QLineEdit
delete:  wid-0                 # delete old parent

call guichange
QRadioButton                     # tmp is QRadioButton
add: QRadioButton parent: wid-2  # set to wid-2 as the parent of QRadioButton
delete:  wid-1                   # delete old parent
delete:  QLineEdit               # message printed by the lambda function 
delete:  QLineEdit               # indicating that QLineEdit has been deleted

call guichange
wrapped C/C++ object of type QLineEdit has been deleted # you want to use QLineEdit 
                                                        # but it had been removed
                                                        # previously causing 
                                                        # that error message

如果要交换小部件,适当的选项是 QStackedWidget 如下所示:

class window25(QtWidgets.QMainWindow):
    def __init__(self):
        super(window25, self).__init__()
        self.lineedit = QtWidgets.QLineEdit()
        self.checkbox = QtWidgets.QCheckBox()
        self.optBox = QtWidgets.QRadioButton()
        self.btn = QtWidgets.QPushButton("press me")
        wid = QtWidgets.QWidget()
        myLayout=QtWidgets.QVBoxLayout()
        self.stacked = QtWidgets.QStackedWidget()
        self.stacked.addWidget(self.lineedit)
        self.stacked.addWidget(self.checkbox)
        self.stacked.addWidget(self.optBox)
        wid.setLayout(myLayout) 
        myLayout.addWidget(self.btn)
        myLayout.addWidget(self.stacked)
        self.setCentralWidget(wid)
        self.guichange()
        self.btn.clicked.connect(self.guichange)

    def guichange(self):
        widget = random.choice([self.lineedit,self.checkbox,self.optBox])
        self.stacked.setCurrentWidget(widget)

if __name__ == '__main__':
    app=QtWidgets.QApplication(sys.argv)
    ex=window25()
    ex.show()
    sys.exit(app.exec_())