re-send an event to a newly enabled child widget

Question

NOTE: below is in edit with a more complete example

I want to implement the following in Qt (specifically PyQt, but I believe that the solution will be similar in both python and C++):

I want a widget to have an internal widget that is disabled by default, and when clicked, the widget will be enabled, and the mouse press will propagate to it. For example, in the following window/widget:

If I click between the c and d, I'd like the QLineEdit to become enabled, take focus, and the cursor to be between the c and d. I got as far as re-enabling the QLineEdit but I can't seem to send the event back to it.

This is my code so far:

from PyQt5.QtWidgets import QWidget, QLineEdit, QVBoxLayout, QPushButton, QApplication


class MyWidget(QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        layout = QVBoxLayout(self)
        self.edit = QLineEdit('abcdef')
        self.edit.setEnabled(False)
        layout.addWidget(self.edit)

        self.disable_btn = QPushButton('disable edit')
        self.disable_btn.clicked.connect(self._disable_edit)
        layout.addWidget(self.disable_btn)

    def _disable_edit(self, *a):
        self.edit.setEnabled(False)

    def mousePressEvent(self, a0):
        if not self.edit.isEnabled() and self.edit.underMouse():
            self.edit.setEnabled(True)
            QApplication.instance().sendEvent(self.edit, a0)  # <-- this doesn't seem to work
        super().mousePressEvent(a0)


if __name__ == '__main__':
    from PyQt5.QtWidgets import QApplication

    app = QApplication([])
    w = MyWidget()
    w.show()
    res = app.exec_()
    exit(res)

This is a simplified example, I also want to wrap other widgets in this way, so that modifying the inner widgets is practically impossible.

The problem is, as far as as I can tell, that the disabled child widget rejects the mouse event (since it is disabled), and refuses to take it (or any other event) again from the parent widget.

Any help at all would be greatly appreciated.

EDIT: following is a clearer example of what I mean:

from PyQt5.QtWidgets import QWidget, QVBoxLayout, QPushButton


class ComplexInnerWidget(QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        layout = QVBoxLayout(self)
        self.btn1 = QPushButton('button 1')
        self.btn1.clicked.connect(self._btn1_click)
        layout.addWidget(self.btn1)

        self.btn2 = QPushButton('button 2')
        self.btn2.clicked.connect(self._btn2_click)
        layout.addWidget(self.btn2)

    def _btn1_click(self, *a):
        print('button 1')

    def _btn2_click(self, *a):
        print('button 2')


class MyWidget(QWidget):
    def __init__(self, inner_widget: QWidget, *args, **kwargs):
        super().__init__(*args, **kwargs)

        layout = QVBoxLayout(self)
        self.inner = inner_widget
        self.inner.setEnabled(False)
        layout.addWidget(self.inner)


if __name__ == '__main__':
    from PyQt5.QtWidgets import QApplication

    app = QApplication([])

    inner = ComplexInnerWidget()
    w = MyWidget(inner)
    w.show()
    res = app.exec_()
    exit(res)

what I want is to allow the user to press the disabled inner widget, hereby enabling it in its entirety (i.e. both btn1 and btn2 becoming enabled), and pressing the appropriate button at the same time. I need this done without changing ComplexInnerWidget at all (since the user should be able to enter any widget as a parameter to MyWidget)

EDIT 2: eyllanesc's solution works for the example provided, but I have adjusted it for MyWidget to be able to support multiple widgets, and to be nested in other widgets:

from PyQt5 import QtCore, QtWidgets


class ComplexInnerWidget(QtWidgets.QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        layout = QtWidgets.QVBoxLayout(self)
        self.btn1 = QtWidgets.QPushButton('button 1')
        self.btn1.clicked.connect(self._btn1_click)
        layout.addWidget(self.btn1)

        self.btn2 = QtWidgets.QPushButton('button 2')
        self.btn2.clicked.connect(self._btn2_click)
        layout.addWidget(self.btn2)

        self.le = QtWidgets.QLineEdit('abcdef')
        layout.addWidget(self.le)

    def _btn1_click(self, *a):
        print('button 1')

    def _btn2_click(self, *a):
        print('button 2')


class MyWidget(QtWidgets.QWidget):
    class EnableMouseHelper(QtCore.QObject):
        def __init__(self, *args, warden):
            super().__init__(*args)
            self.warden = warden

        def eventFilter(self, obj, event):
            if obj.isWidgetType() and event.type() == QtCore.QEvent.MouseButtonPress:
                if self.warden in obj.window().findChildren(QtWidgets.QWidget) \
                        and self.warden.underMouse() and not self.warden.isEnabled():
                    self.warden.setEnabled(True)
                obj.setFocus()
            return super().eventFilter(obj, event)

    def __init__(self, inner_widget: QtWidgets.QWidget, *args, **kwargs):
        super().__init__(*args, **kwargs)
        layout = QtWidgets.QVBoxLayout(self)
        self.inner = inner_widget
        self.inner.setEnabled(False)
        layout.addWidget(self.inner)
        self.helper = self.EnableMouseHelper(warden=self.inner)
        QtWidgets.QApplication.instance().installEventFilter(self.helper)


class OuterWidget(QtWidgets.QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        layout = QtWidgets.QVBoxLayout(self)
        layout.addWidget(MyWidget(ComplexInnerWidget()))

        layout.addWidget(MyWidget(ComplexInnerWidget()))

        le = QtWidgets.QLineEdit('hi there')
        le.setEnabled(False)
        layout.addWidget(le)

        le = QtWidgets.QLineEdit('hi there')
        layout.addWidget(le)


if __name__ == '__main__':
    from PyQt5.QtWidgets import QApplication

    app = QApplication([])
    w = OuterWidget()
    w.show()
    res = app.exec_()
    exit(res)

eyllanesc · Accepted Answer · 2019-03-06T09:08:22.057

You can not send the event object since Qt will delete it when the widget consumes it, what you must do is create another event with the same data. I have created a class that allows you to register widgets to give you this property without having to overwrite the class.

from functools import partial
from PyQt5 import QtCore, QtGui, QtWidgets

class Singleton(type(QtCore.QObject), type):
    def __init__(cls, name, bases, dict):
        super().__init__(name, bases, dict)
        cls.instance=None

    def __call__(cls,*args,**kw):
        if cls.instance is None:
            cls.instance=super().__call__(*args, **kw)
        return cls.instance

class EnableMouseHelper(QtCore.QObject, metaclass=Singleton):
    def __init__(self, parent=None):
        super(EnableMouseHelper, self).__init__(parent)
        self._widgets = []

    @staticmethod
    def addWidget(widget):
        if isinstance(widget, QtWidgets.QWidget):
            helper = EnableMouseHelper()
            helper._widgets.append(widget)
            widget.installEventFilter(helper)
            return True
        return False

    @staticmethod
    def removeWidget(widget):
        helper = EnableMouseHelper()
        if widget is helper._widgets:
            widget.removeEventFilter(helper)
            helper._widgets.remove(widget)

    def eventFilter(self, obj, event):
        if obj in self._widgets and event.type() == QtCore.QEvent.MouseButtonPress:
            if not obj.isEnabled():
                new_event = QtGui.QMouseEvent(
                    event.type(),
                    event.localPos(),
                    event.windowPos(),
                    event.screenPos(),
                    event.button(),
                    event.buttons(),
                    event.modifiers(),
                    event.source()
                )
                obj.setEnabled(True)
                obj.setFocus()
                QtCore.QCoreApplication.postEvent(obj, new_event)
        return super(EnableMouseHelper, self).eventFilter(obj, event)


class ComplexWidget(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(ComplexWidget, self).__init__(parent)

        le_1 = QtWidgets.QLineEdit(text='abcdef', enabled=False)
        btn_le_1 = QtWidgets.QPushButton(text='disable edit', clicked=partial(le_1.setEnabled, False))
        EnableMouseHelper.addWidget(le_1) # <---- register widget

        le_2 = QtWidgets.QLineEdit(text='abcdef', enabled=False)
        btn_le_2 = QtWidgets.QPushButton(text='disable edit', clicked=partial(le_2.setEnabled, False))
        EnableMouseHelper.addWidget(le_2) # <---- register widget

        flay = QtWidgets.QFormLayout(self)
        flay.addRow(le_1, btn_le_1)
        flay.addRow(le_2, btn_le_2)

if __name__ == '__main__':
    import sys
    app = QtWidgets.QApplication(sys.argv)
    w = ComplexWidget()
    w.show()
    sys.exit(app.exec_())

Update: It is not necessary to forward the event, just enough to enable the widget.

from PyQt5 import QtCore, QtGui, QtWidgets

class EnableMouseHelper(QtCore.QObject):
    def eventFilter(self, obj, event):
        if obj.isWidgetType() and event.type() == QtCore.QEvent.MouseButtonPress:
            for w in obj.window().findChildren(QtWidgets.QWidget):
                if not w.isEnabled():
                    w.setEnabled(True)
            obj.setFocus()
        return super(EnableMouseHelper, self).eventFilter(obj, event)

class ComplexInnerWidget(QtWidgets.QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        layout = QtWidgets.QVBoxLayout(self)
        self.btn1 = QtWidgets.QPushButton('button 1')
        self.btn1.clicked.connect(self._btn1_click)
        layout.addWidget(self.btn1)

        self.btn2 = QtWidgets.QPushButton('button 2')
        self.btn2.clicked.connect(self._btn2_click)
        layout.addWidget(self.btn2)

        self.le = QtWidgets.QLineEdit('abcdef')
        layout.addWidget(self.le)

    def _btn1_click(self, *a):
        print('button 1')

    def _btn2_click(self, *a):
        print('button 2')


class MyWidget(QtWidgets.QWidget):
    def __init__(self, inner_widget: QtWidgets.QWidget, *args, **kwargs):
        super().__init__(*args, **kwargs)
        layout = QtWidgets.QVBoxLayout(self)
        self.inner = inner_widget
        self.inner.setEnabled(False)
        layout.addWidget(self.inner)

if __name__ == '__main__':
    from PyQt5.QtWidgets import QApplication
    app = QApplication([])
    helper = EnableMouseHelper()
    app.installEventFilter(helper)
    inner = ComplexInnerWidget()
    w = MyWidget(inner)
    w.show()
    res = app.exec_()
    exit(res)

This solution doesn't seem to work with more complex widgets (like a `QWidget` with an internal layout) — bentheiii, Mar 04 '19 at 13:52
@bentheiii I have improved my implementation and I have added an example with a complex Widget, the trick is to register the QLineEdit as sample is my example. — eyllanesc, Mar 04 '19 at 18:34
Okay, but this doesn't actually enable/disable the entire complex widget at once, only lineedits. This also requires that the internal widget class `ComplexWidget` is modified. — bentheiii, Mar 05 '19 at 04:47
@bentheiii If you want more help you should provide an [MCVE] where it is clear that you call a ComplexWidget since it seems that your idea of ComplexWidget is very different from mine. For example, in the image that your shows consider the ComplexWidget is the widget that has as children the QLineEdit and QPushButton and clearly is not disabled (that is what I have taken as a basis for my answer). If you do then you tell me :-) — eyllanesc, Mar 05 '19 at 04:51

score 0 · Answer 2 · answered Feb 24 '19 at 20:17

Try it:

from PyQt5.QtWidgets import QWidget, QLineEdit, QVBoxLayout, QPushButton, QApplication

class LineEdit(QLineEdit):                                    # +++
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.setText('abcdef')
        self.setStyleSheet('color: blue; font-size: 32px')

    def mousePressEvent(self, event):
        super(LineEdit, self).mousePressEvent(event)
        self.cursor = self.cursorPosition() 

    def mouseReleaseEvent(self, event):
        self.setFocus()
        self.setCursorPosition(self.cursor)  


class MyWidget(QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        layout    = QVBoxLayout(self)

#        self.edit = QLineEdit('abcdef')
        self.edit = LineEdit()                                  # +++

        self.edit.setEnabled(False)
        layout.addWidget(self.edit)

        self.disable_btn = QPushButton('disable edit')
        self.disable_btn.clicked.connect(self._disable_edit)
        layout.addWidget(self.disable_btn)

    def _disable_edit(self, *a):
        self.edit.setEnabled(False)

    def mousePressEvent(self, a0):
        if not self.edit.isEnabled() and self.edit.underMouse():
            self.edit.setEnabled(True)
            QApplication.instance().sendEvent(self.edit, a0)  # <-- this does seem to work
        super().mousePressEvent(a0)


if __name__ == '__main__':
    from PyQt5.QtWidgets import QApplication
    app = QApplication([])
    w = MyWidget()
    w.show()
    res = app.exec_()
    exit(res)

This might work for a lineedit, but I'd like to enable other (client provided) widgets in this way, so that configuring them in this way is ineffective. — bentheiii, Feb 26 '19 at 09:27
As the example above, except you can substitute the `QLineEdit('abcdef')` with a user-provided widget (as a parameter to `__init__` maybe) — bentheiii, Feb 26 '19 at 10:38

re-send an event to a newly enabled child widget

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