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.
Related
There are hundreds of widgets in QVBoxLayout. I am hiding/showing them based on option menus. If I hide some of widgets, some blank space remains in QVBoxLayout and I dont want this unnecessary space. Adding spacer at bottom is not solving the issue. Same for setting margin spacing. Its like hidden widgets consume some space. Is there any way to fix this?
Thanks.
Layouts have some default spacing between each child widget, defined by setSpacing(), setHorizontalSpacing(), setVerticalSpacing(). Even if you hide the child widget, the spacing around it remains visible. (Note: I think this is a bad design decision made by Qt developers, but we need to live with it.) You have basically these options:
a) Remove the child widget from the layout instead of hiding it. Remember its original position and if it should be shown again, insert it at that position. This is complicated, the original position may be invalidated if you removed some other widgets meanhile, so this would require some clever algorithm for maintaining the correct visual positions of the hidden child widgets in the layout etc. I would not do this, feels too complicated for me.
b) Use zero-sized default spacing in the layout and add spacings manually by https://doc.qt.io/qt-5/qboxlayout.html#addSpacing and then when hiding the child widgets, set the size of the QSpacerItem next to it to zero. And set it back to non-zero when showing the child widget again.
c) Alternative to a) but do not keep original indexes but have a container of pointers to the child widgets and when a change in the visibility of the child widgets is required, then remove all the items from the layout and put all the child widgets which should be visible to the layout. This means to re-create the content of the layout in each change. Actually this is how I am doing it in my code. I have about 20 widgets and hiding/showing is fast enough. I believe it will be fast enough even for hundreds of widgets.
d) And alternative to c) ... if you have really large number of widgets, then you should consider deleting those which are not supposed to be visible and re-creating them when they are shown. I.e. in c) we keep the widget alive but hidden in a certain container but in d) we delete this widget and create it later again. It depends on your use case whether c) is better than d) or vice versa. My gut feeling is that c) should be fine performance-wise and is simpler.
Note: My reasonging is based on showing and hiding of widgets in grid layout, but I guess that VBox layout has the same principles regarding preserving default spacing even around hidden items.
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 want to add scroll bars to the frame container. the QscrollArea can only take on widget but in my frame I need many wigets
I tried to write a code for the bars after adding a horizantal and vertical one but It's too hard.Is there any pre-made free code I could use ?
thank you
QScrollArea can take any number of widgets - indirectly. The widget() can contain any number of child widgets, it can have a layout set, etc. See e.g. this answer.
In Qt, how can I have a widget which automatically sizes itself according to the size of it's children?
For example, if I have a QGroupBox which contains a QHBoxLayout which contains some QPushButtons, I would like the QGroupBox to automatically calculate it's size so that it is no bigger and no smaller than necessary to fit all of the QPushButtons.
Ideally I would like to be able to do this in Qt Designer so that I can create a .ui file which already knows how to size the QGroupBox, however I am also opening to deriving from a class inside a .ui file and doing the resizing manually.
I have tried placing the QGroupBox inside it's own layout (with and without a spacer) but this just resizes the QGroupBox to the smallest possible size so that none of the children are visible.
There are two things to pay attention to:
Set the size policies appropriately on the children in the groupbox. You literally need to think what the buttons can do - most likely, you do not want the buttons to either grow or shrink, so setting both of their size policies to Fixed is the right thing to do. You could, possibly, let the buttons expand horizontally, so the horizontal policy of MinimumExpanding is an option.
Set the size constraint on the layout in the groupbox to act according to your objective:
ui->groupbox->layout()->setConstraint(QLayout::SetMinAndMaxSize);
Of course, the groupbox will be inside of some layout in its parent window, but that doesn't matter.
You'll probably have the most luck by sub classing QGroupBox and overriding sizeHint or other sizing functions to loop through children and calculate the minimum bounding rectangle. Depending on how dynamic the group box is, managing connections to new widgets might be a small challenge.
I am having a problem redrawing a QWidget window after its size has been adjusted. I have tried update(), repaint(), adjustSize(), but all seem to suffer from the same thing: only part of the window is redrawn, resulting in the window frame on the bottom and right sides to not show. The window is also not resized entirely.
Just in case it makes a difference, the window is in a QMdiArea.
Thanks.
// ... some subwidget resizing and moving.
calibrationWindowUIs[activeWindow].layoutWidget2->move(QPoint(oldXLeft, 30 + height + 21));
calibrationWindowUIs[activeWindow].layoutWidget1->move(QPoint(oldXRight, 30 + height + 21));
// Set window size.
calibrationWindows[activeWindow]->setMinimumSize(calibrationWindowUIs[activeWindow].tabWidget->geometry().width() + 40, calibrationWindowUIs[activeWindow].tabWidget->geometry().height() + 40);
calibrationWindows[activeWindow]->update();
Note: I'm new to Qt; perhaps I'm doing something wrong with layouts?
Edit: I may have not given enough information. Alright, to be quite honest, I still have to delve deeper into layouts and related material. What I had tried to do here was to use Qt Designer in order to design the window. I've done what perhaps amounts to a stupid mistake: I didn't use an overall parent layout for the entire window, but hacked it with a couple of smaller layouts that I therefore have to move about and resize individually. See the Qt Designer screen (the red rectangles are the sole layouts): .
What is happening is that in the frame to the right, I am playing a video clip that can be of various resolutions. I want the frame to resize depending on this resolution, which also means that the buttons and window have to move/resize accordingly. That is where the window resize comes in. I'm sure there is a more elegant solution than what I am doing here, but I am trying to handle several other scenarios here and hence the lack of quality of code.
The result is that when I load a clip, the window attempts to resize, but does so badly; the following is the result:
If the window is dragged, it 'pops' into its correct size; in the meantime, however, it just looks ugly.
A couple further questions: do you use the Qt Designer to design your UIs? I found that programmatically you can achieve much better control of your interfaces. One thing which I could not do in the designer was to have a layout parented by the main widget, i.e. the equivalent of having the following bit of code:
QVBoxLayout* layout = new QVBoxLayout;
this->setLayout(layout);
A layout placed in the designer always seems to create this 'layoutWidget' subwidget, which the layout you placed is then parented to. Any way around that?
We use a mix of designer and code to create layouts, the Qt layout system can be very unintuitive at times. But I would probably not layout a full series of tabs in one designer ui file, i would make each tab each own widget and then assemble them either through code or in the designer by promoting to custom classes. This gives you better separation of responsibilities, by putting all the functionality of all the tabs into one file you almost guarantee a large unwieldy class.
When a widget has child widgets in designer you can assign a layout to it by adding it from the context menu. Make sure nothing is selected and click on the background of the widget in which you want to create a layout, select the layout and all of the widgets children will be assigned the layout.
What does help is creating hierarchies of layouts. Looking at your first screenshot, i would probably use a vertical layout with spacers on top and bottom for the items on the right, an horizontal layout with spacers left and right for the button bar and a grid layout for all the items together. Without the spacers your items will extend when the window grows. The spacers will let you control the behavior under resizing better.
you are calling setMinimumSize(). That's fine, but you should also call resize()