This is a bit of a beginners question but I don't find the solution.
I'm using an own object that inherits from QLineEdit and reiceves numbers as input (which works smoothly now).
Now I want to receive an event, when the user presses the Escape-button. This does not happen with the textChanged()-event. According to the documentation there is no special escape-event. So how else can this be done?
Thanks!
I had this same problem. I am solving it by implementing keyPressEvent in my QMainWindow.
void MainWindow::keyPressEvent(QKeyEvent *e)
{
if (e->key() == Qt::Key_Escape) {
QLineEdit *focus = qobject_cast<QLineEdit *>(focusWidget());
if (lineEditKeyEventSet.contains(focus)) {
focus->clear();
}
}
}
And setting up QSet<QLineEdit *> lineEditKeyEventSet to contain the QLineEdits that need this behavior.
void MainWindow::setupLineEditKeyEventList()
{
lineEditKeyEventSet.insert(ui->lineEdit_1);
lineEditKeyEventSet.insert(ui->lineEdit_2);
lineEditKeyEventSet.insert(ui->lineEdit_3);
}
You can either implement keyPressEvent :
void LineEdit::keyPressEvent(QKeyEvent *event)
{
if (event->key() == Qt::Key_Escape)
{
...
}
QLineEdit::keyPressEvent(event);
}
Or implement eventFilter :
bool LineEdit::eventFilter(QObject *obj, QEvent * event)
{
if((LineEdit *)obj == this && event->type()==QEvent::KeyPress && ((QKeyEvent*)event)->key() == Qt::Key_Escape )
{
...
}
return false;
}
When using the eventFilter approach, install the event filter in the constructor :
this->installEventFilter(this);
Related
In Delphi I often made an OnAfterShow event for the main form. The standard OnShow() for the form would have little but a postmessage() which would cause the OnafterShow method to be executed.
I did this so that sometimes lengthy data loading or initializations would not stop the normal loading and showing of the main form.
I'd like to do something similar in a Qt application that will run on a desktop computer either Linux or Windows.
What ways are available to me to do this?
You can override showEvent() of the window and call the function you want to be called with a single shot timer :
void MyWidget::showEvent(QShowEvent *)
{
QTimer::singleShot(50, this, SLOT(doWork());
}
This way when the windows is about to be shown, showEvent is triggered and the doWork slot would be called within a small time after it is shown.
You can also override the eventFilter in your widget and check for QEvent::Show event :
bool MyWidget::eventFilter(QObject * obj, QEvent * event)
{
if(obj == this && event->type() == QEvent::Show)
{
QTimer::singleShot(50, this, SLOT(doWork());
}
return false;
}
When using event filter approach, you should also install the event filter in the constructor by:
this->installEventFilter(this);
I solved it without a timer using Paint event. Works for me at least on Windows.
// MainWindow.h
class MainWindow : public QMainWindow
{
...
bool event(QEvent *event) override;
void functionAfterShown();
...
bool functionAfterShownCalled = false;
...
}
// MainWindow.cpp
bool MainWindow::event(QEvent *event)
{
const bool ret_val = QMainWindow::event(event);
if(!functionAfterShownCalled && event->type() == QEvent::Paint)
{
functionAfterShown();
functionAfterShownCalled = true;
}
return ret_val;
}
Using the mouse events of QWidget it is possible to catch the user's interaction with the widget. However, Qt does not deliver only the resulting action (a click or a double click), but provides the whole sequence of events as it is. Thus, the action should be recognized manually and my question is: How? QMouseEvent::flags() doesn't help much, since the only flag Qt::MouseEventCreatedDoubleClick is never set, as reported here.
In other words, how to properly emit those two signals, defined in the header file of MyWidget (derived from QWidget):
void clicked();
void doubleClicked();
having those slots:
void MyWidget::mousePressEvent(QMouseEvent *event)
{
...
}
void MyWidget::mouseReleaseEvent(QMouseEvent *event)
{
...
}
void MyWidget::mouseDoubleClickEvent(QMouseEvent *event)
{
...
}
By properly I mean that if the user double clicks MyWidget only MyWidget::doubleClicked should be emited instead of MyWidget::clicked followed by MyWidget::doubleClicked;
I met the same problem before. I think it is by design of Qt. This may not be a best solution, but what you can do is to create an event filter and 'wait' for a while:
bool m_bClicked = false;
bool eventFilter(QObject* object, QEvent* event)
{
if(event->type() == QEvent::MouseButtonPress)
{
// Wait for 400 milliseconds
m_bClicked = true;
QTimer::singleShot(400, this, SLOT(eventMousePressTimer()));
return true;
}
else if(event->type() == QEvent::MouseButtonDblClick)
{
// Double-clicked
m_bClicked = false;
return true;
}
return false;
}
void eventMousePressTimer()
{
if(m_bClicked)
{
// Single-clicked
}
}
I Have a Form with several LineEdits and other Elements and want to jump from one to the next by pressing the return key.
I find Return key instead of/additional to the tab key more user friendly.
I can probably do it if i use returnPressed() and setFocus() but i hope there is a better more elegant solution for this.
Is there a way to modify the built in tab order to also work with
return?
If not, what are the best ways to accomplish the above?
You're probably looking for the event handler. ( QEvent )
Example from the doc
bool MyWidget::event(QEvent *event)
{
if (event->type() == QEvent::KeyPress) {
QKeyEvent *ke = static_cast<QKeyEvent *>(event);
if (ke->key() == Qt::Key_Tab) {
// special tab handling here
return true;
}
} else if (event->type() == MyCustomEventType) {
MyCustomEvent *myEvent = static_cast<MyCustomEvent *>(event);
// custom event handling here
return true;
}
return QWidget::event(event);
}
It's easily adjustable to any key.
For example if return is pressed simulate a tab key press event.
As mentioned, it is more efficient to override QWidget::keyPressEvent
Some code:
protected:
void keyPressEvent(QKeyEvent *event) override;
void MyWidget::keyPressEvent(QKeyEvent *event){
if(event->key()==Qt::Key_Return){
this->focusNextChild();
}
}
Background
I've made a custom widget with QLineEdit and several QPushButtons to use it with custom item delegate:
class LineEditor : public QWidget
{
public:
explicit LineEditor(QWidget *parent = 0) : QWidget(parent) {
setLayout(new QHBoxLayout);
layout()->setContentsMargins(0, 0, 0, 0);
layout()->setSpacing(0);
QLineEdit *edit = new QLineEdit(this);
layout()->addWidget(edit);
layout()->addWidget(new QPushButton(this));
layout()->addWidget(new QPushButton(this));
setFocusProxy(edit);
}
};
class PropertyDelegate : public QItemDelegate
{
public:
QWidget *createEditor(QWidget *parent, const QStyleOptionViewItem &option, const QModelIndex &index) const {
return new LineEditor(parent);
}
bool eventFilter(QObject *object, QEvent *event) {
if (event->type() == QEvent::KeyPress) {
qDebug() << "KeyPress";
}
if (event->type() == QEvent::ShortcutOverride) {
qDebug() << "ShortcutOverride";
}
return QItemDelegate::eventFilter(object, event);
}
};
I'm going to bind them with QListView and QStandardItemModel like this:
QStandardItemModel *model = new QStandardItemModel;
model->appendRow(new QStandardItem("1"));
model->appendRow(new QStandardItem("2"));
model->appendRow(new QStandardItem("3"));
QListView w;
w.setItemDelegate(new PropertyDelegate);
w.setModel(model);
w.show();
Question
Why in the PropertyDelegate::eventFilter when Tab key is pressed there is only QEvent::ShortcutOverride event, but pressing of any other key emits both QEvent::ShortcutOverride and QEvent::KeyPress events?
UPD: I want to implement the moving between lines by pressing Tab and Backtab like with standard widgets.
Well, finally I've done some research about that.
Explanation
When a view calls createEditor function of delegate it also installs the delegate event filter to editor.
QWidget *QAbstractItemViewPrivate::editor(const QModelIndex &index,
const QStyleOptionViewItem &options)
{
Q_Q(QAbstractItemView);
QWidget *w = editorForIndex(index).widget.data();
if (!w) {
QAbstractItemDelegate *delegate = delegateForIndex(index);
if (!delegate)
return 0;
w = delegate->createEditor(viewport, options, index);
if (w) {
w->installEventFilter(delegate);
......
}
However the delegate can catch only events of editor widget, but not events of its children. When the Tab key is pressed the QWidget::event function is called, it uses it to change focus to another widget:
bool QWidget::event(QEvent *event)
{
......
switch (event->type()) {
......
case QEvent::KeyPress: {
QKeyEvent *k = (QKeyEvent *)event;
bool res = false;
if (!(k->modifiers() & (Qt::ControlModifier | Qt::AltModifier))) { //### Add MetaModifier?
if (k->key() == Qt::Key_Backtab
|| (k->key() == Qt::Key_Tab && (k->modifiers() & Qt::ShiftModifier)))
res = focusNextPrevChild(false);
else if (k->key() == Qt::Key_Tab)
res = focusNextPrevChild(true);
if (res)
break;
}
......
}
......
}
Accordingly in my case the focus is set to next QPushButton after QLineEdit and event isn't propagated to the parent (LineEditor).
Solving
The right way to solve the problem is like QSpinBox does it. Because it is also has QLineEdit. In constructor of widget it sets focus proxy for line edit:
edit->setFocusProxy(this);
So all of focus events will reach the main widget. Also the focusPolicy property must be set because it's NoFocus by default:
setFocusPolicy(Qt::WheelFocus);
All we need to do in this moment it is to propagate necessary events to QLineEdit from main widget like this:
bool LineEditor::event(QEvent *e)
{
switch(e->type())
{
case QEvent::ShortcutOverride:
if(m_lineEdit->event(e))
return true;
break;
case QEvent::InputMethod:
return m_lineEdit->event(e);
default:
break;
}
return QWidget::event(e);
}
void LineEditor::keyPressEvent(QKeyEvent *e)
{
m_lineEdit->event(e);
}
void LineEditor::mousePressEvent(QMouseEvent *e)
{
if(e->button() != Qt::LeftButton)
return;
e->ignore();
}
void LineEditor::mouseReleaseEvent(QMouseEvent *e)
{
e->accept();
}
void LineEditor::focusInEvent(QFocusEvent *e)
{
m_lineEdit->event(e);
QWidget::focusInEvent(e);
}
void LineEditor::focusOutEvent(QFocusEvent *e)
{
m_lineEdit->event(e);
QWidget::focusOutEvent(e);
}
This should be enough.
Tricky
As it's said above the delegate can't catch events of editor's children. So to make editor's behavior like "native" I have to duplicate events from children to editor.
LineEditor installs event filter to QLineEdit in constructor:
edit->installEventFilter(this);
Implementation of filter looks like this:
bool LineEditor::eventFilter(QObject *object, QEvent *event)
{
if(event->type() == QEvent::KeyPress)
{
QKeyEvent* keyEvent = static_cast<QKeyEvent *>(event);
if(keyEvent->key() == Qt::Key_Tab || keyEvent->key() == Qt::Key_Backtab)
{
QApplication::postEvent(this, new QKeyEvent(keyEvent->type(), keyEvent->key(), keyEvent->modifiers()));
// Filter this event because the editor will be closed anyway
return true;
}
}
else if(event->type() == QEvent::FocusOut)
{
QFocusEvent* focusEvent = static_cast<QFocusEvent *>(event);
QApplication::postEvent(this, new QFocusEvent(focusEvent->type(), focusEvent->reason()));
// Don't filter because focus can be changed internally in editor
return false;
}
return QWidget::eventFilter(object, event);
}
It's also possible to use qApp->notify(this, event) for QKeyEvent instead of QApplication::postEvent because we filter this events anyway. But it's not possible for QFocusEvent because notify will redirect the event and it will not reach a child.
Note that the standard (QItemDelegate or QStyledItemDelegate) delegate will care about situation when focus is changed internally by itself:
if (event->type() == QEvent::FocusOut || (event->type() == QEvent::Hide && editor->isWindow())) {
//the Hide event will take care of he editors that are in fact complete dialogs
if (!editor->isActiveWindow() || (QApplication::focusWidget() != editor)) {
QWidget *w = QApplication::focusWidget();
while (w) { // don't worry about focus changes internally in the editor
if (w == editor)
return false;
w = w->parentWidget();
}
......
I have a control with several QSpinBox objects inside a QScrollArea. All works fine when scrolling in the scroll area unless the mouse happens to be over one of the QSpinBoxes. Then the QSpinBox steals focus and the wheel events manipulate the spin box value rather than scrolling the scroll area.
I don't want to completely disable using the mouse wheel to manipulate the QSpinBox, but I only want it to happen if the user explicitly clicks or tabs into the QSpinBox. Is there a way to prevent the QSpinBox from stealing the focus from the QScrollArea?
As said in a comment to an answer below, setting Qt::StrongFocus does prevent the focus rect from appearing on the control, however it still steals the mouse wheel and adjusts the value in the spin box and stops the QScrollArea from scrolling. Same with Qt::ClickFocus.
In order to solve this, we need to care about the two following things:
The spin box mustn't gain focus by using the mouse wheel. This can be done by setting the focus policy to Qt::StrongFocus.
The spin box must only accept wheel events if it already has focus. This can be done by reimplementing QWidget::wheelEvent within a QSpinBox subclass.
Complete code for a MySpinBox class which implements this:
class MySpinBox : public QSpinBox {
Q_OBJECT
public:
MySpinBox(QWidget *parent = 0) : QSpinBox(parent) {
setFocusPolicy(Qt::StrongFocus);
}
protected:
virtual void wheelEvent(QWheelEvent *event) {
if (!hasFocus()) {
event->ignore();
} else {
QSpinBox::wheelEvent(event);
}
}
};
That's it. Note that if you don't want to create a new QSpinBox subclass, then you can also use event filters instead to solve this.
Try removing Qt::WheelFocus from the spinbox' QWidget::focusPolicy:
spin->setFocusPolicy( Qt::StrongFocus );
In addition, you need to prevent the wheel event from reaching the spinboxes. You can do that with an event filter:
explicit Widget( QWidget * parent=0 )
: QWidget( parent )
{
// setup ...
Q_FOREACH( QSpinBox * sp, findChildren<QSpinBox*>() ) {
sp->installEventFilter( this );
sp->setFocusPolicy( Qt::StrongFocus );
}
}
/* reimp */ bool eventFilter( QObject * o, QEvent * e ) {
if ( e->type() == QEvent::Wheel &&
qobject_cast<QAbstractSpinBox*>( o ) )
{
e->ignore();
return true;
}
return QWidget::eventFilter( o, e );
}
edit from Grant Limberg for completeness as this got me 90% of the way there:
In addition to what mmutz said above, I needed to do a few other things. I had to create a subclass of QSpinBox and implement focusInEvent(QFocusEvent*) and focusOutEvent(QFocusEvent*). Basically, on a focusInEvent, I change the Focus Policy to Qt::WheelFocus and on the focusOutEvent I change it back to Qt::StrongFocus.
void MySpinBox::focusInEvent(QFocusEvent*)
{
setFocusPolicy(Qt::WheelFocus);
}
void MySpinBox::focusOutEvent(QFocusEvent*)
{
setFocusPolicy(Qt::StrongFocus);
}
Additionally, the eventFilter method implementation in the event filter class changes its behavior based on the current focus policy of the spinbox subclass:
bool eventFilter(QObject *o, QEvent *e)
{
if(e->type() == QEvent::Wheel &&
qobject_cast<QAbstractSpinBox*>(o))
{
if(qobject_cast<QAbstractSpinBox*>(o)->focusPolicy() == Qt::WheelFocus)
{
e->accept();
return false;
}
else
{
e->ignore();
return true;
}
}
return QWidget::eventFilter(o, e);
}
My attempt at a solution. Easy to use, no subclassing required.
First, I created a new helper class:
#include <QObject>
class MouseWheelWidgetAdjustmentGuard : public QObject
{
public:
explicit MouseWheelWidgetAdjustmentGuard(QObject *parent);
protected:
bool eventFilter(QObject* o, QEvent* e) override;
};
#include <QEvent>
#include <QWidget>
MouseWheelWidgetAdjustmentGuard::MouseWheelWidgetAdjustmentGuard(QObject *parent) : QObject(parent)
{
}
bool MouseWheelWidgetAdjustmentGuard::eventFilter(QObject *o, QEvent *e)
{
const QWidget* widget = static_cast<QWidget*>(o);
if (e->type() == QEvent::Wheel && widget && !widget->hasFocus())
{
e->ignore();
return true;
}
return QObject::eventFilter(o, e);
}
Then I set the focus policy of the problematic widget to StrongFocus, either at runtime or in Qt Designer.
And then I install my event filter:
ui.comboBox->installEventFilter(new MouseWheelWidgetAdjustmentGuard(ui.comboBox));
Done. The MouseWheelWidgetAdjustmentGuard will be deleted automatically when the parent object - the combobox - is destroyed.
Just to expand you can do this with the eventFilter instead to remove the need to derive a new QMySpinBox type class:
bool eventFilter(QObject *obj, QEvent *event)
{
QAbstractSpinBox* spinBox = qobject_cast<QAbstractSpinBox*>(obj);
if(spinBox)
{
if(event->type() == QEvent::Wheel)
{
if(spinBox->focusPolicy() == Qt::WheelFocus)
{
event->accept();
return false;
}
else
{
event->ignore();
return true;
}
}
else if(event->type() == QEvent::FocusIn)
{
spinBox->setFocusPolicy(Qt::WheelFocus);
}
else if(event->type() == QEvent::FocusOut)
{
spinBox->setFocusPolicy(Qt::StrongFocus);
}
}
return QObject::eventFilter(obj, event);
}
With help from this post we cooked a solution for Python/PySide. If someone stumbles across this. Like we did :]
class HumbleSpinBox(QtWidgets.QDoubleSpinBox):
def __init__(self, *args):
super(HumbleSpinBox, self).__init__(*args)
self.setFocusPolicy(QtCore.Qt.StrongFocus)
def focusInEvent(self, event):
self.setFocusPolicy(QtCore.Qt.WheelFocus)
super(HumbleSpinBox, self).focusInEvent(event)
def focusOutEvent(self, event):
self.setFocusPolicy(QtCore.Qt.StrongFocus)
super(HumbleSpinBox, self).focusOutEvent(event)
def wheelEvent(self, event):
if self.hasFocus():
return super(HumbleSpinBox, self).wheelEvent(event)
else:
event.ignore()
This is my Python PyQt5 port of Violet Giraffe answer:
def preventAnnoyingSpinboxScrollBehaviour(self, control: QAbstractSpinBox) -> None:
control.setFocusPolicy(Qt.StrongFocus)
control.installEventFilter(self.MouseWheelWidgetAdjustmentGuard(control))
class MouseWheelWidgetAdjustmentGuard(QObject):
def __init__(self, parent: QObject):
super().__init__(parent)
def eventFilter(self, o: QObject, e: QEvent) -> bool:
widget: QWidget = o
if e.type() == QEvent.Wheel and not widget.hasFocus():
e.ignore()
return True
return super().eventFilter(o, e)
Just to help anyone's in need, it lacks a small detail:
call focusInEvent and focusOutEvent from QSpinBox :
void MySpinBox::focusInEvent(QFocusEvent* pEvent)
{
setFocusPolicy(Qt::WheelFocus);
QSpinBox::focusInEvent(pEvent);
}
void MySpinBox::focusOutEvent(QFocusEvent*)
{
setFocusPolicy(Qt::StrongFocus);
QSpinBox::focusOutEvent(pEvent);
}