According to the docs, QGraphicsSceneEvent::widget() returns a QWidget. Isn't the widget always going to be a QGraphicsView, though (or null)?
I would assume so, except then I don't understand why the devs wouldn't have just made it QGraphicsSceneEvent::view().
The reason I'm asking is that in my subclassed QGraphicsScene, I have overridden QGraphicsScene::mousePressEvent() and I want to know which view originated the event--I'm wondering if it's safe to static cast widget() to a QGraphicsView, or if it's conceivable that some other widget could have created the event.
As it turns out, QGraphicsSceneEvent::widget() returns the viewport widget, not the QGraphicsView. If you want the QGraphicsView, you would need to use: event->widget()->parent().
Documentation page you refered mentions the QGraphicsView as a target of events:
When a QGraphicsView receives Qt mouse, keyboard, and drag and drop
events (QMouseEvent, QKeyEvent, QDragEvent, etc.), it translates them
into instances of QGraphicsSceneEvent subclasses and forwards them to
the QGraphicsScene it displays. The scene then forwards the events to
the relevant items.
However, if you doubt that QGraphicsSceneEvent::widget() always returns QGraphicsView, or you relay that it should always be a QGraphicsView you can check that by using qobject_cast:
QGraphicsView *view = qobject_cast<QGraphicsView *>(event->widget();
if (view) {
// Handle the event
} else {
// This is something that I do not expect.
// ..
}
Related
I have a application in Qt, and a MainWindow. Now, I also added a helping QDialog which can be hooked up. This QDialog does not influence the programmflow, it just displays information.
But, it always starts on top of the MainWindow :/
SO I would like to start it on the side of the main window, so that it does not hinder the view to the main window?? How?
In my opinion , You should try this,
Use the overload of the QWidget::setParent() function to change the ownership of a QDialog widget, using set as NULL(but It will not share the parent's taskbar entry).
QDialog::show() returns control to the caller immediately, So it will not interfere in mainwindow flow.
Let's say, your application is in the full screen mode. Where then the QDialog should appear? It will be shown on the top and you won't be satisfied again.
If it doesn't influence the flow of the app then you are using it to communicate some sort of message. Can you use different ways? For instance, QStatusBar?
If not, why not to split the mainWindow with QSplitter or similar classes and provide an area where you can post all the info messages?
It sounds you want modaless dialog. In main window, use a slot to create the dialog.
void MainWindow::show_dialog()
{
if ( pDialog== NULL )
pDialog= new XYZ_Dialog(this);
QPoint p = pos();
QSize s = frameSize();
pDialog->setGeometry(p.x()+s.width(), p.y(), s.width()*1/2, s.height());
pDialog->show();
}
What I try to say is if the position of the new dialog bothers you, you set the position and size of it, before showing it.
I got a QGraphicsScene that contains QGraphicsItems. On clicking such an item I open a dialog. I now want the item to be displayed in an area of the dialog.
I tried a QGraphicsView (in the dialog) and "pointed" it to the item which works allmost perfectly. The problem is, that it is possible to click the item in the dialog which would open a new dialog.
So my question: is there a easy way to tell QGraphicsView to ignore any input events? If not, is there a easy way to display a QGraphicsItem within a widget?
I am feeling so stupid...
QGraphicsView::setInteractive(false) did the trick.
I am still able to move the icon with the mouse wheel but this can probably be avoided by restricting the scene rect with setSceneRect()
You can install an event filter, on the QGraphicsView, which ignores input events. The Qt documentation states:
In your reimplementation of this function, if you want to filter the event out, i.e. stop it being handled further, return true; otherwise return false.
I'm developing a custom widget with QGraphicsScene/View and I have no prior experience with it.
The custom widget is an image viewer that needs to track mouse movement and send signal(s) to it's parent dialog / window. The signal(s) will be the position of the pixel under the mouse cursor and it's color (in RGB). A status bar will use that information.
I use a QGraphicsPixmapItem to display the image I load from a file in the scene.
Thanks.
First of all you have to implement the mouseMoveEvent in your custom item. In this function you can easily get the mouse position calling the pos function. You can get the rgb value if you transform the item's pixmap into image and call the pixel function. You should consider storing the QImage as member variable in order to avoid multiple transformations. Finally you have to emit a custom signal. Sample code follows:
void MyPixmapItem::mouseMoveEvent(QGraphicsSceneMouseEvent * event)
{
QPointF mousePosition = event->pos();
QRgb rgbValue = pixmap().toImage().pixel(mousePosition.x(), mousePostion.y());
emit currentPositionRgbChanged(mousePosition, rgbValue);
}
Notice that QGraphicsItems do not inherit from QObject so by default signals/slots are not supported. You should inherit from QObject as well. This is what QGraphicsObject does. Last but not least I would advise you to enable mouse tracking on your QGraphicsView
I found the mouseMoveEvent approach to not work at all, at least not with Qt5.5. However, enabling hover events with setAcceptHoverEvents(true) on the item and reimplementing hoverMoveEvent(QGraphicsSceneHoverEvent * event) worked like a charm.
The Qt docs on mouseMoveEvent() provide the clue:
"If you do receive this event, you can be certain that this item also received a mouse press event"
http://doc.qt.io/qt-5.5/qgraphicsitem.html#mouseMoveEvent
I have a QGLWidget as part of the UI of my application. It is NOT a central widget, there are a lot of others widgets around it. I want to show it full screen on user clicks the button. Similar functionality like on youtube video flash player.
I have tried to use showFullScreen with no effect.
I have read how-to-fullscreen-a-qglwidget and fullscreen-widget, but they suggest using showFullScreen.
Qt documentation states that for using showFullScreen widget must be an independent window. So I assume there should be some trick for this.
The solution I found:
void MyApp::on_fullscreen_button_clicked() {
QDialog *dlg = new QDialog(this);
QHBoxLayout *dlg_layout = new QHBoxLayout(dlg);
dlg_layout->setContentsMargins(0, 0, 0, 0);
dlg_layout->addWidget(glwidget_);
dlg->setLayout(dlg_layout);
dlg->showFullScreen();
bool r = connect(dlg, SIGNAL(rejected()), this, SLOT(showGlNormal()));
assert(r);
r = connect(dlg, SIGNAL(accepted()), this, SLOT(showGlNormal()));
assert(r);
}
void MyApp::showGlNormal() {
ui.glBox->layout()->addWidget(glwidget_);
}
The showFullScreen function works only on windows. From the Qt documentation:
A window is a widget that isn't visually the child of any other widget
and that usually has a frame and a window title.
A possible solution is the following:
When the user clicks the show full screen button
Create a new QGlWidget with no parent and set to it the contents of you QGlWidget
Use the showFullScreen function on it...
Maybe it is a better idea to subclass QGlWidget and pass in its constructor a pointer to another QGlWidget. The constructor should take the context of the provided widget and apply it to the new one.
On your subclass catch keyboard events. When the user press Esc emit a signal
In your base class catch this signal and connect it to a slot. In this slot hide the full screen QGlWidget and delete it.
I want an app's main window to ignore mouse and keyboard events, passing them to applications underneath it in the window manager Z-order.
I see how to make child widgets ignore keyboard or mouse events, but how about the main window?
I'm trying to make a desktop widget that always sits just over the background and is totally invisible to keyboard and mouse events. (Pass through)
Qt::X11BypassWindowManagerHint gets me keyboard pass through (although sadly X11 specific, but fine for now), so how about mouse events?
Is there a OS-agnostic way to be transparent to keyboard events?
EDIT:
The key word here is transparency.
I don't want to EAT mouse and keyboard events, I want the window manager to know I don't want them at all. Those events should be directed to whatever application is under me in the zorder.
For example, I want to be able to click on desktop icons that are covered by my widget and interact with them as if the widget was not there.
I found the following solution (tested on Linux, also works on Windows according to #TheSHEEEP):
setWindowFlags(windowFlags() | Qt::WindowTransparentForInput);
It has been added in more recent qt release (i did not find when)
see http://doc.qt.io/qt-5/qt.html
On Windows you can set WS_EX_TRANSPARENT
To do this in Qt use the following code:
Include the header,
#if _WIN32
#include <windows.h>
#endif
and put the following code into the constructor.
#if _WIN32
HWND hwnd = (HWND) winId();
LONG styles = GetWindowLong(hwnd, GWL_EXSTYLE);
SetWindowLong(hwnd, GWL_EXSTYLE, styles | WS_EX_TRANSPARENT);
#endif
Maybe what you want is
widget->setAttribute(Qt::WA_TransparentForMouseEvents)
? That's what QRubberBand uses to let it's parent handle the mouse events. As for keyboard events, a QWidget doesn't get any keyboard events unless it has set itself a focusPolicy().
setFocusPolicy( Qt::NoFocus );
should therefore take care of the keyboard events.
Use Qt's event filters: they will allow your application to eat whichever events you specify (i.e. keyboard and mouse events) but still process other events such as paint events.
bool FilterObject::eventFilter(QObject* object, QEvent* event)
{
QKeyEvent* pKeyEvent = qobject_cast<QKeyEvent*>(event);
QMouseEvent* pMouseEvent = qobject_cast<QMouseEvent*>(event);
if (pKeyEvent || pMouseEvent)
{
// eat all keyboard and mouse events
return true;
}
return FilterObjectParent::eventFilter(object, event);
}
Maybe I'm missing something here, but have you tried subclassing the QMainWindow class and overriding the QWidget::event() method to always return false? If you need to handle some events, you could add that intelligence here as well.
This technique should allow you to inspect the events coming in to the application and ignore them if desired without having to eat them using an event filter.
If this doesn't work you could attempt to redirect the events to the desktop by calling QCoreApplication::notify() and passing the event to the desktop widget obtained by calling QApplication::desktop(). I have no idea if this would work, but it seemed like it might be worth giving a try.
I think that overriding is supposed to work:
bool YourMainWindow::event( QEvent *event )
{
event ->accept();
return true;
}
that's some of what the QWidget class documentation says about event() member function:
This function returns true if the
event was recognized, otherwise it
returns false. If the recognized event
was accepted (see QEvent::accepted),
any further processing such as event
propagation to the parent widget
stops.