My main application window is constructed as follows:
A QVBoxLayout;
In its upper cell there is a horizontal QSplitter;
In its lower cell there is a QFrame with QHBoxLayout.
Now, when I add widgets to either QSplitter or QHBoxLayout and there is no room left in them, they both stretch themselves indefinitely (and go offscreen if they can) instead of shrinking the widgets they contain. For the QHBoxLayout part, I tried combining setSizeConstraint(QLayout::SetMaximumSize) with various ways of setting QFrame's width, to no avail. It still stretches uncontrollably. For the QSplitter part, I don't even know what to begin with.
So, what is the magic (and apparently undocumented - I spent 2 hours googling) API call combo for making Qt widget containers shrink their children instead of growing themselves?
Related
How to add an image to a dialog in Qt?
I know this has been often asked in the past and most answers come up with a QLabel and its setPixmap member. However, this usually is not what the user (me) intends:
A QLabel with a pixmap set does not participate in the surrounding QLayout. That is, it simply refuses to resize when the dialog is resized, like e.g., a QPushButton would do. Two QPushButtons next to each other in a QHorizontalLayout will (something like) equally divide the available horizontal space between them. A QLabe with a pixmap next to a QPushButton in the same layout will just stay fixed in size.
By default, a naked QLabel won't resize its contents when it's resized.
But when it does (QLabel::setResizeContents) it won't keep aspect ratio.
Is there any native way to have a pixmap shown on a dialog and have it reasonably participate in the layout?
Item resizing can be managed via sizePolicy property. From Qt documentation:
sizePolicy : QSizePolicy
This property holds the default layout behavior of the widget.
If there is a QLayout that manages this widget's children, the size
policy specified by that layout is used. If there is no such QLayout,
the result of this function is used.
The default policy is Preferred/Preferred, which means that the widget
can be freely resized, but prefers to be the size sizeHint() returns.
Button-like widgets set the size policy to specify that they may
stretch horizontally, but are fixed vertically. The same applies to
lineedit controls (such as QLineEdit, QSpinBox or an editable
QComboBox) and other horizontally orientated widgets (such as
QProgressBar). QToolButton's are normally square, so they allow growth
in both directions. Widgets that support different directions (such as
QSlider, QScrollBar or QHeader) specify stretching in the respective
direction only. Widgets that can provide scroll bars (usually
subclasses of QScrollArea) tend to specify that they can use
additional space, and that they can make do with less than sizeHint().
I think you are searching for QSizePolicy::Expanding size policy:
The sizeHint() is a sensible size, but the widget can be shrunk and
still be useful. The widget can make use of extra space, so it should
get as much space as possible (e.g. the horizontal direction of a
horizontal slider).
Set this for your QLabel and check how it will resize. Try other values from QSizePolicy::Policy enum.
I have a Qt application which has a window based on a QWdiget. Inside my window I have two QVBoxLayouts and one QHBoxLayout with controls underneath the first two Vertical layouts. When my window is resized, the QVBoxLayout move apart and the QHBoxLayout underneath also moves away. I want to prevent this from happening, what is the best way to do this?
All these layouts are inside a QGridLayout.
If I understand your question correctly, you have a window's layout like this :
The layouts is going to resize depending on the size of the objects in them. To solve your problem, you should set the alignment of your layouts within the grid layout using setAlignment method.
by the way, if nothing works, you can always write your own layout manager.
I want to place some widgets in a parent widget in some random places, like one button at Point (10,10) and another at (15,40), etc. How to achieve this?. QGridLayout is pushing everything into row column style. But I want to put the widgets whereever I want,Can anybody help me?
If you really want to set absolute positions, I would ignore using a layout altogether. You can manually set the positions of elements by using the move() function or the setGeometry() function.
QWidget *parent = new QWidget();
parent->resize(400, 400);
QPushButton *buttonA = new QPushButton(parent);
buttonA->setText("First Button");
buttonA->move(10, 10);
QPushButton *buttonB = new QPushButton(parent);
buttonB->setText("Second Button");
buttonB->move(15, 40);
Side note: I would avoid setting absolute positions of elements in Qt. Why? Well, Qt tries to be a platform-independent GUI library. On different platforms, a lot of display things can change (i.e. font size of text in push buttons) so the size of your actual push buttons can vary to accommodate large or smaller font sizes. This can throw off your meticulously spaced push buttons is you use absolute positions as in the example above.
If you use layouts, overlapping buttons or buttons falling off the edge of your window can be avoided.
You can see my answer for overlay button in QT: Qt Widget Overlays. This may help you to achieve what you want.
How do you change the behavior of a QListWidget so that it resizes its height instead of choosing a (seemingly arbitrary) height and adding scrollbars? See screenshot:
The QListView's should fill up as much space horizontally as they can (creating as many "columns," if you will.) Then they wrap and make as many rows as necessary to fit all the items. These calculations should be adjusted as the window is resized. This is all working fine.
However, what I want to happen is that instead of the height staying the same, the QListView should grow or shrink vertically and never need any scrollbars. The scrolling, if necessary, will be handled on the parent QWidget that hosts all of the labels and lists. It seems like once the height of the QListWidget is established (not sure where its default is coming from), it never changes. It is too big in some cases (see second "Test" list above) and too small in others (see first "blank maps" list above.)
The layout above is nothing surprising: two QLabel's and two QListWidget's in a QVBoxLayout. Here are the properties I have set on the QListWidget's:
setMovement(QListView::Static);
setResizeMode(QListView::Adjust);
setViewMode(QListView::IconMode);
setIconSize(QSize(128, 128));
(I already tried setting the horizontal and vertical scrollbar policies, but that just turns the scrollbars off, clipping the content. Not what I want.)
Maybe you could this without using QListWidget. The Qt's examples contain a new layout class, QFlowLayout, which could be useful. With the following kind of widget hierarchy you could get multiple groups with labels and they all would be inside one QScrollArea.
QScrollBox
QVBoxLayout
QLabel "Blank maps"
QWidget
QFlowLayout
your own widgets showing map images and labels
QLabel "Text"
QWidget
QFlowLayout
your own widgets
The problem is that this kind of solution would create much more widgets than QListWidget based solution. So if you have hundreds of items in your list, this might not be the best solution.
There is a protected member function called contentsSize() in QListView. It is used to calculate the required minimum(), maximum(), and pageStep() for the scrollbars (as mentioned here).
Can you subclass the QListView class and make use of that information? I suggest you recalculate the size of your widget in the same function where you add contents to it. While somewhat lacking elegance, this appears to be a pretty reliable solution.
I'm creating some graphic data displaying widget in Qt4 and I was tempted to use the QGraphicsScene for it, create QGraphicsItems for the data items etc.
However, I wanted to add some layer of controls (eg. scrollbars, zoom+other buttons - I want to make it in a similar style as eg. Google Maps, that is, the data would be displayed all over the widget, and the buttons would be shown atop of them) to the widget. So I thought it might be feasible to add them to the scene (perhaps as a child of a QGraphicsGroupItem that would be shown over the data). But I want them to move & resize when I resize the whole widget, so I should use a QGraphicsLayout for managing them. But at this point, I discovered things are pretty complicated.
The problem is that when using QGraphicsLayout, the following constraints hold:
Only a QGraphicsWidget can be managed by a layout
QGraphicsLayout can only be used to manage children of a QGraphicsWidget
Which means that I would have to create my controls as QGraphicsWidgets, add a top level QGraphicsWidget to the data widget, and manage the size of this top level widget myself.
So I want to ask:
Wouldn't a classic approach (ie. use plain old widgets for all controls, and use QGraphicsScene only for displaying the data) be more reasonable?
Is there any advantage in using QGraphicsScene in this case (performance or simplicity...)?
How should I use QGraphicsScene to exploit its strengths?
Since Qt 4.4 you can embed classic widgets in a QGraphicsScene by using QGraphicsProxyWidget :
QWidget *widget = new QWidget;
QGraphicsScene scene;
QGraphicsProxyWidget *proxy = scene.addWidget(widget);
If you think that QGraphicsScene (or whatever other widget you have) is appropriate for most of your display, use that. What we have done in the past for somewhat similar things is to make a custom widget that inherits (one way or another) from QWidget, and put the control widgets in a layout on top of that widget. This means that the whole widget is drawing whatever it is you want drawn, and the control widgets are on top of that, resizing as the whole widget is resized.
Alternatively, a couple of times we've had layouts that were just a bit too complicated for the layout widgets to easily handle. Rather than create a custom layout, we just positioned them with no layout, and moved them in code on the resize event. It works just as well.