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.
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 the following, quite simple setup:
In a QWidget that is displayed as a window (no parent), there is a single QVBoxLayout.
In that QVBoxLayout, there is a single custom QGraphicsView.
The size policy of that custom QGraphicsView is set to Preferred/Preferred and setHeightForWidth set to true (and overwritten in the custom class) - I want to preserve aspect ratio.
The whole constructor of the widget here:
graphicsView = new CustomGraphicsView();
QVBoxLayout *layout = new QVBoxLayout();
layout->setMargin(0);
QSizePolicy sp(QSizePolicy::Preferred, QSizePolicy::Preferred);
sp.setHeightForWidth(true);
graphicsView->setSizePolicy(sp);
layout->addWidget(graphicsView);
setLayout(layout);
The setup works, and the aspect ratio is maintained when dragging the width of the window bigger (the height grows with it).
But as soon as I drag the window width smaller, the aspect ratio of the graphics view is maintained, but the height of the window itself won't shrink. The result being a small graphics view with lots of space above and below it that shouldn't be there.
Investigating it further I was trying to find out where things break, so I overloaded all the sizeHint(), minimumSize(), minimumHeight(), etc. functions of my custom graphics view.
Just to discover that not a single one of them is ever being called while I am manually resizing the window. The only thing called as expected is heightForWidth - which returns my calculated value - but its return value is not applied when the window is shrinking.
So, not only do I not know why the layout won't shrink on its own despite having the Preferred vertical policy (which explicity says "The widget can be expanded, but there is no advantage to it being larger than sizeHint()").
I also don't know how the layout gets the size from the widget to begin with. I assumed sizeHint() since all of the documentation permanently refers to it, but that is obviously wrong in this case.
What I already tried is to set the vertical policy to every possible value. None of them would cause the window to grow and shrink as it is supposed to.
My current workaround:
I have added the resizeEvent(...) function to the widget and inside that, I manually resize() the whole widget if its height exceeds the value returned by the heightForWidth() function of the custom graphics widget.
Okay as far as workarounds go, but it leads to heavy flickering (as usual when resizing inside a resizeEvent).
Any ideas on either problem?
I have a simple qt application with a QTabWidget inside the main window. I also have a few QPushButton(s) and QRadioButton(s).
What I want is that when I resize the window either manually or by maximizing/minimizing it should resize the containers in the same way.
In other words, what I want is equivalent of DockStyle.Fill in qt C++
How can I do that ?
In Qt you have to use Layouts:
The Qt layout system provides a simple and powerful way of automatically arranging child widgets within a widget to ensure that
they make good use of the available space.
In short, all components in a layout will be relocated to new places after the window, to which the layout belongs, is resized.
If you are using deisgner:
1. Click the empty space of a widget to select itself(or a main Window, I use just a base widget here for demonstration), and the layout option will be hightlighted:
2. Choose a desired layout
Here is what object monitor looks like after a QVBoxLayout is used:
If your widget doesn't use layout, it will look like this:
What we have done here is to make the base widget/mainWindow equip a main layout. You can see that the buttons are automatically aligned, when you resize the widget, those component will be relocated according to the layout:
Perhaps you will find it nettlesome of those expanding space, so the next move is to add a Spacer to the layout; so when layout is resized, only the spacer will stretch.
(Another option is to make your widgets expandable, see ** at the end of this post)
3. Besides, you can add a layout into another to create a nested layout
For example, first I choose A and B (by pressing Ctrl) and use QVBoxLayout. This additional layout is not base layout and hence highlighted by red rectangle.
Then I choose C and the layout which contains A & B, and use QHBoxLayout on them,
Finally I use another QVBoxLayout as my main layout on the base widget, just like what we did previously.
And the object monitor:
If you like the special feeling of hitting keyboard and always handcraft the code:
For the last example:
QWidget *Form = new QWidget;
QPushButton *pushButton_A = new QPushButton("A");
QPushButton *pushButton_B = new QPushButton("B");
QPushButton *pushButton_C = new QPushButton("C");
QVBoxLayout *verticalLayout = new QVBoxLayout;
QHBoxLayout *horizontalLayout = new QHBoxLayout;
QVBoxLayout *mainLayout = new QVBoxLayout;
verticalLayout->addWidget(pushButton_A);
verticalLayout->addWidget(pushButton_B);
horizontalLayout->addWidget(pushButton_C);
horizontalLayout->addLayout(verticalLayout);
mainLayout->addLayout(horizontalLayout);
Form->setLayout(mainLayout);
Form->show();
In your case
Here is an example of layout:
Notice that QMainWidget has a centralwidget as a base widget. Besides, each tab of QTabWidget has it's own base widget (tab and tab_2 in the picture) which adopts another base layout.
*Don't forget to add Spacer in layouts to shape them as you like.
** You can set size policy on each widget (QTabWidget, QPushButton etc) to make them horizontally/vertically expandable or fixed, this cooperates with the layout strategy. For example, in the very begin example if we set
button A to be vertically fixed, horizontally expanding
button B to be vertically expanding, horizontally expanding
button C to be vertically expanding, horizontally fixed
It will look like this when resizing:
you need to look into how to use layouts in your application
http://qt-project.org/doc/qt-4.8/layout.html
As a quick and simple first try, in the Designer you can right-click on the main window, and choose "layout" from the drop-down menu. Here you can pick the grid layout, for instance.
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 have a QDialog with a QVBoxLayout controlling its height.
This main QVBoxLayout consists of one or more QVBoxLayout children, followed by some other widgets. As I add additional QVBoxLayout children, (and/or lower widgets) the dialog box expands to accommodate them - as you would expect, and as I want.
However, when I remove QVBoxLayout children from the parent QVBoxLayout, the dialog box is not resized smaller by the amount equal to the size of the QVBoxLayout that was removed - it just remains the same size with unsightly large blank areas.
How do I achieve the correct dynamic behaviour in QVBoxLayout/QDialog, such that the dialog box is resized properly when child components are removed from the QVBoxLayout?
Make sure you call mainLayoutPtr->setSizeConstraint(QLayout::SetFixedSize) (this will also make the dialog not resizable by user, but it will be able to properly resize when widgets hide/show)
If you don't want to make the dialog non-resizable, you can resize it manually after any child is deleted:
QApplication::processEvents();
dialog->resize(dialog->sizeHint());
QWidget::adjustSize() is what you are looking for:
Adjusts the size of the widget to fit its contents.
This function uses sizeHint() if it is valid, i.e., the size hint's width and height are >= 0. Otherwise, it sets the size to the children rectangle that covers all child widgets (the union of all child widget rectangles).
For windows, the screen size is also taken into account. If the sizeHint() is less than (200, 100) and the size policy is expanding, the window will be at least (200, 100). The maximum size of a window is 2/3 of the screen's width and height.
Docs - http://doc.qt.digia.com/4.7/qwidget.html#adjustSize