I need an event for detecting if an user has moved the scrollbar position to another one.
In other words, if the user does scroll up/down, would it be possible to catch a signal so I can know the scroll has been changed its position?
I think it's not important, but the scrollbar I refer to is inside a QGraphicsView.
Regards.
Edit:
QGraphicsView is for displaying items in the screen, and if those items are too big it shows the scrollbars I refer to. What I need is to know when the user changes the position of those scrollbars.
Sliders have a sliderMoved(int value) signal, where value is the new position of slider.
If you need to get notified when the scroll bar position is changed, you need to subclass the QGraphicsView and reimplement the QWidget::mouseMoveEvent(QMouseEvent*). For this you also need to enable mouse tracking. Here is Qt 4.7 QGraphicsView reference.
Related
I'm getting started with Qt and decided to build a full-screen text editor. I want to have a button (button with arrow in screenshot) attached to a QDockWidget which opens and closes it so the button is always visible to the right side of the screen and stay anchored to it when dock is visible or resized.
My current app is a simple fullscreen textEdit set to centeralwidget in Mainwindow.
I haven't found a way to do this yet with layouts or existing addAnchor() functions so any help or direction is appreciated.
You can achieve what you want by using a container for your text edit and the button. A QWidget instance can be used as an "invisible"*** container for other widgets.
So in Qt Designer you add a widget as a central widget of the main-window, inside this widget you add the text edit and the button, then you set a vertical layout for this container widget.
Don't forget to restrict the docking widget to only dock to the right side, you can do that with: dock->setAllowedAreas(Qt::DockWidgetArea::RightDockWidgetArea); //assuming dock is the pointer to your QDockWidget.
In case you want the dockWidget to be able to dock to any side and the button to follow, you can do that too, but it get a little bit more complicated. Basically you need to connect a slot to dockLocationChanged of your dockWidget and based on where it's docked you need to set-up a new layout for the container widget to be vertical or horizontal and the order of the textEdit and the button based on the side the dock happened.
LE:*** you will most likely need to set the margins you want, since both the widget and it's layout can have them and the actual content might have higher spacing than you want.
I wish to make a custom graphics item to follow the cursor without needing to be clicked on. My view has setMouseTracking(true), my graphics item has setFlag(ItemIsMovable, true); setAcceptHoverEvents(true);, but it doesn't track the cursor, I have to click and drag it. What is the proper way to make a QGraphicsItem follow the cursor?
You can only capture mouse event on an item if your cursor pass above it. For example, instead of clicking on the item, you can react on mouseMove events.
But you seem to want a more global behaviour. You could track mouseMoveEvent directly on your QGraphicsView (or on your QGraphicsScene if you have multiple views) (see mouseMoveEvent). After that, just keep a reference on your item and make it move each time you intercept an event
I need to detect if the mouse pointer leaves my custom widget even if a mouse button is pressed.
According to this post, Qt does not cause a leaveEvent in case a button is pressed, at least not in version 4.4. I am working with 4.7.3, but still do not get a leaveEvent in the described case. I also tried with the various drag-related events, but no luck. Does anyone have an idea how to deal with this?
Actually there is an even better option than using the mouse events of the parent widget: You can implement the mouseMoveEvent function of the child widget and get the QMouseEvent::pos() position which is relative to the top left corner of the widget. That means, if you know the size of the widget (use for example QWidget::rect()), you can compute within the widget if the mouse pointer is still on the widget or not without having to change the parent widget.
Well, I did something similar to #gregseth.
Write your own MouseLeaveEvent that is invoked from MouseMoveEvent
when the mouse's position is outside of the widget's boundary.
As Qt's documentation says "Mouse move events will occur only when a mouse button is pressed down"
I got the same problem. The only workaround I found is to manage the mouseMove event of the parent widget, and to check if the position of the cursor is inside or outside the boundaries of the widget you want the event on.
I'm writing an image viewer as a custom Qt widget (see: https://github.com/dov/Qviv) and I now got stuck on the question of how to make my widget notify a parent QScrollArea of changes in the view port, and thus to tell it to move the scrollbars. E.g. if the image viewer changes the zoom factor as the result of a keypress then the scrollbars need to change their page size.
One way of doing it would be to have the widget explicitly check if the parent is a QScrollArea and then make an explicit call to its methods to notify it on any changes.
Of course I also need to connect the changes of the ScrollArea to the internal view of the image, but that is a different question. And I need to cut the infinite recursion where the widget reports changes to the scrollbar that report changes to the widget etc.
Edit 20:15 Wednesday (GMT/UTC) trying to clarify to Vjo and myself what I need.
What I am trying to achieve is the equivalent of a Gtk widget that has been assigned a pair of GtkAdjustment's that are connected to a horizontal and vertical scrollbar. In my widget GtkImageViewer, that QvivImageViewer is based on, whenever I change the view due to some internal event (e.g. a keypress) I update the GtkAdjustment's. The scrollbars are connected to such changes and are update accordingly. GtkImageViewer also listens to the GtkAdjustment changes, and thus if the user scrolls the scrollbars, the GtkImageViewer is updated with this information and can change its view. My question is whether there is anything similar to GtkAdjustment in Qt that you can connect to for changes, and update in which case the update will be propagated to all the listeners?
Thus I don't expect the ScrollArea to be part of QvivImageViewer, but if the user has placed QvivImageViewer within a ScrollArea, I want bidirectional communication with it so that the scrollbars reflect the internal state of the widget.
The simplest is to send the QResizeEvent event from your widget object to the QScrollArea object.
I finally downloaded the Qt sources and investigated how QTextEdit does it. What I found is that QTextEdit inherits the QAbstractScrollArea on its own, and thus the scroll area and the scrollbars are part of the widget. This is different from Gtk, which uses a higher level of abstraction, through its GtkAdjustment's that are used to signal changes between the scrollbars and the widget. The Qt model is simpler and this is the way that I will implement it in my widget.
It's been a while, but I ran across this same issue.
You can inherit QAbstractScrollArea if you'd like, but QScrollArea will work as well.
Your custom inner widget (i.e. the one that you are scrolling), should do the following when its size changes:
void MyCustomControl::resize_me() {
// recompute internal data such that sizeHint() returns the new size
...
updateGeometry();
adjustSize();
}
QSize MyCustomControl::sizeHint() {
return ... ; // Return my internally computed size.
}
I was missing the adjustSize() call, and without it the QScrollArea will ignore size changes of the internal widget.
I've got a long horizontal QLabel displaying a png (the image shows a signal/time graph). Under that, I've got a QTableWidget. Both of these are in a QScrollArea because I want them to stay vertically aligned (the cells in the table correspond with the signal seen directly above them). I'm trying to add a handler to the QLabel such that the user can use the picture itself to scroll the scrollarea, rather than having to use the scrollbar. Is there a tried-and-tested way to do this? Directly setting the scrollarea's sliderPosition inside the QLabel's dragMoveEvent doesn't seem smart, because when the scrollarea scrolls it also leads to another dragMoveEvent on the (moving) QLabel.
I would suggest wrapping the combination (including the scroll area) in their own widget, and overriding the dragMoveEvent() on that widget. The dragMoveEvent() shouldn't be triggered when you change the scroll position if you are doing it this way, I wouldn't think, although I haven't actually tested it.