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.
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 MainWindow in qt with a Tab Widget attached, containing a tab called "tab_upload".
On this tab i got a label with the text "Genres" (it's a library application) with a "plus" button attached. I want to be able to get a new QLineEdit every time I click this button , positioned inline with the other ones. To get the right coordonates is easy but I'm not able to properly set the geometry of the new QLineEdit. It doesn't matter what I type in the setGeometry function, the QLineEdit will always appear in the center.
And also, if I press the button a second time I get an error saying
QWidget::setLayout: Attempting to set QLayout "" on QWidget "tab_upload", which already has a layout.
if(nr_genres < 4)
{
QLineEdit *newgen = new QLineEdit(ui->tab_upload);
int x = 5 + nr_genres * 90;
newgen->setGeometry(x,187,90,25);
QVBoxLayout *layout = new QVBoxLayout;
layout->addWidget(newgen);
ui->tab_upload->setLayout(layout);
}
Layouts are designed to have control over the positioning of widgets:
All QWidget subclasses can use layouts to manage their children. The QWidget::setLayout() function applies a layout to a widget. When a layout is set on a widget in this way, it takes charge of the following tasks:
Positioning of child widgets.
Sensible default sizes for windows.
Sensible minimum sizes for windows.
Resize handling.
Automatic updates when contents change:
Font size, text or other contents of
child widgets.
Hiding or showing a child widget.
Removal of child widgets.
You should read this documentation for information about adding widgets to layouts:
All the widgets will initially be allocated an amount of space in accordance with their QWidget::sizePolicy() and QWidget::sizeHint().
If any of the widgets have stretch factors set, with a value greater than zero, then they are allocated space in proportion to their stretch factor (explained below).
If any of the widgets have stretch factors set to zero they will only get more space if no other widgets want the space. Of these, space is allocated to widgets with an Expanding size policy first.
Any widgets that are allocated less space than their minimum size (or minimum size hint if no minimum size is specified) are allocated this minimum size they require. (Widgets don't have to have a minimum size or minimum size hint in which case the stretch factor is their determining factor.)
Any widgets that are allocated more space than their maximum size are allocated the maximum size space they require. (Widgets do not have to have a maximum size in which case the stretch factor is their determining factor.)
I think that the easiest way to manage widgets in layouts is to use the Design mode in Qt Creator, and specify a minimumSize and/or maximumSize for each widget, along with a sizePolicy. This way, you can see what happens and experiment with different values.
With regards to the error you're receiving, it is mentioned in the documentation for setLayout():
If there already is a layout manager installed on this widget, QWidget won't let you install another. You must first delete the existing layout manager (returned by layout()) before you can call setLayout() with the new layout.
QWidget::setLayout: Attempting to set QLayout "" on QWidget
"tab_upload", which already has a layout.
You set new layout on widget that already contains layout from previous click on "plus" button. This problem can be solve by next way:
QLineEdit *newgen = new QLineEdit(ui->tab_upload);
QVBoxLayout *layout = static_cast<QVBoxLayout*>(ui->tab_upload->layout());
if(!layout) {
layout = new QVBoxLayout(ui->tab_upload);
ui->tab_upload->setLayout(layout);
}
layout->addWidget(newgen);
But you cannot directly set geometry for your QLineEdit because geometry was set by layout. If I understand the problem, this code must help you. It creates new QLineEdit after each click on "plus" button and append QLineEdit to existing layout.
I have a complex layout of widgets in widgets in widgets in a QMainWindow. In one of them I have an image, it sits in the corner. What I would like to achieve is following: if the image is activated (e.g. clicked upon), it should be enlarged, so it might overlap other widgets, or parts of other widgets. The problem is, I still would like it to remain in the layout, but in a way that everything else remains in its original size and position.
I was thinking about having an empty but similar size widget as a "placeholder", and have the actual resizable widget float on top of it. My problem is, that it does not guarantee that it stays in its position if the main window is resized, maximized, etc. Is there a better or more efficient way to do it?
One way to do it, if the widgets to be overlapped are in the same layout than the one you want to enlarge, and the policies for that widget allow it, is just .setVisible(false) in the other widgets. The widget that remains visible should resize to cover all the available area!
If I can't find a better solution, I think I'll do the following:
The MainWindow will have no layout, just two QWidgets on top of each other. The bottom one will contain all the layouts and everything else, while the upper one will have a transparent background and the resizable widget, maybe supported with a number of spacers.
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.
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.