I'm building a GUI with Python and Qt. The standard widgets are quite useful and work out of the box. However, I have some ideas about mouse gestures. More precisely, a button or label or text, that, after being clicked ant the mouse held pressed, moving the mouse around around has special effects.
What is necessary to add mouse support for the following events
mouse clicked over widget A while it was visible
mouse moved to x, y (at real time)
mouse released
to an arbitrary widget?
Right now I am trying to do this by class A, which inherits QAbstractItemView and owns a QWidget. However, nothing works AND
NotImplementedError: QAbstractItemView.verticalOffset() is abstract and must be overridden
QAbstractItemView is not helpful for your task.
You can install event filter on an arbitrary widget using installEventFilter. Your filter class must be inherited from QObject. The documentation contains some useful examples. See QObject::installEventFilter. If you want to install filter on all widgets at once, you can install it for QApplication instance.
Another option is to subclass QWidget (or any other QWidget-derived class) and reimplement its mousePressEvent, mouseMoveEvent and mouseReleaseEvent virtual functions.
Related
There is a "entered" signal for a QTreeView Widget, which I can use to check if my mouse moves over an item.
Is there a way to implement an "left" signal?
Why:
I have a treeView with a lot of items which I also plot via QChart. I want to highlight the plot when someone mouse over the data in the treeview.
I can highlight it via the "entered" signal, but I have no idea how to change it back to the default if the mouse left/mouse is over another item...
entered is a member of QAbstractItemView. You should probably reimplement QAbstractItemView::dragLeaveEvent virtual method.
See this method documentation: http://doc.qt.io/qt-5/qabstractitemview.html#dragLeaveEvent
I have my custom widget inherited from QWidget, and I've connected the widget's menu-calling signal to my slot.
connect(m_ontologyView, SIGNAL(customContextMenuRequested(QPoint)), SLOT(showContextMenuSlot(QPoint)));
Now I want user to be able to change button calling the context menu. Normally it's called with right mouse button, but how do I tell the widget to call the menu with a button of my choice?
I'm on Qt 5.4.0
Instead of using QWidget::customContextMenuRequested, you will need to reimplement the widgets mouse event functions, QWidget::mousePressEvent, QWidget::mouseReleaseEvent and QWidget::mouseMoveEvent. Inside of these events, you can then show you menu using QMenu::popup. (The point can be extracted from the mouse events).
By default QSlider reacts on mouse wheel only when cursor is on it. I want to control slider by mouse wheel not matter where the cursor is (of course only when my application has focus).
What's the best way to achieve that?
I just learned that mouse doesn't generate signals. So looks like I need to override wheelEvent in main window and use raise or lower method in it. But I guess that can cause double increment (or decrement) of slider value when mouse is hovering it.
So once again: What's the best way to achieve what I described?
You can override the wheelEvent() in your MainWindow and redirect it to your slider control, that is indeed one option.
Another option is to install an event filter on the qApp instance. This even filter then can check whether the event type is QEvent::Wheel, and when the receiver is not the slider, then again redirect it to the slider. Should work just as well.
I've recently been studying Qt, and have the following questions:
What is the difference between QAction and QToolButton?
How do I know when to override QPushButton? For example, should I override in order to be informed when the mouse enters a QPushButton's bounds? I don't need to in order to get the signal click().
Question 1:
QActions are used to define tasks performed by an application in a way which can be understood by a number of different user interface objects. Using an example from the Qt docs for context:
A QAction is defined; it is given an icon image, a text description, a keyboard shortcut and a longer tooltip description, as well as being linked to a user defined function.
newAct = new QAction(QIcon(":/images/new.png"), tr("&New"), this);
newAct->setShortcuts(QKeySequence::New);
newAct->setStatusTip(tr("Create a new file"));
connect(newAct, SIGNAL(triggered()), this, SLOT(newFile()));
Later in the implementation, the QAction is added both to a textual menu bar...
fileMenu->addAction(newAct);
... and an icon-based tool bar:
fileToolBar->addAction(newAct);
The menu bar uses the text description to create an entry in the menu corresponding to the action. Similarly the toolbar uses the icon set on the QAction to create an icon in the toolbar which corresponds to the action. Selecting the menu item, clicking the toolbar icon or pressing the keyboard shortcut will all result in the same effect: that defined by the linking of QAction::triggered() to newFile().
So to directly answer your question: a QAction is an abstract way of defining the various parameters and behaviour of a particular task performed by the application. A QToolbarButton is a UI object (derived from QWidget) created by a QToolbar in response to QToolbar::addAction()
Question 2:
Yes, QPushButton has a clicked() signal inherited from QAbstractButton, but it does indeed lack a way to inform when the mouse has entered its bounds. You have a couple of options in order achieve this, but first you need to first set the mouseTracking property to be enabled. This will allow you to receive mouse move events on the QPushButton even if no mouse buttons are pressed. With that done you need to explore one of the following options:
As you suggest, you could subclass QPushButton and reimplement mousePressEvent in order to respond to the mouse position.
You could install another widget as an eventFilter on the QPushButton, and watch for events of type (QEvent::MouseMove).
I have a problem:
I'm creating a widget which displays current date's day number. It's like a button, but it's not derived from QPushButton class. Just from QWidget. So I've reimplemented enterEvent(), leaveEvent(), mousePressEvent(), mouseReleaseEvent(). I do call update() inside these methods and widget has realistic button behavior (paintEvent() is reimplemented also).
But when I change system date and hover that widget with other window, my widget doesn't get paintEvent() and the old date is displayed. Only when I place mouse over it, widget repaints it's contents.
I guess there is a feature (like buffering) which paints old contents on hovering with other window to avoid unnecessary recalculations. But I need to disable it. Tried to set many attributes (the Qt::WidgetAttribute enum). But it doesn't work.
I think you should find a way to detect that the system time has changed and call update() when that happens. Any other method (like detecting the "hovering" of a window or waiting for a mouse event) will cause the update to occur too late.