I am currently working on a Python Project and I would like to create the UI with PyQt5 (preferably with the help of PyQt5 Designer).
I have recently finished a Youtube tutorial about the basics of PyQt5, but I am still at beginner level.
I am currently trying to create the Main Menu of the program.
I would like the Main Menu to look like this (the background image would decorate the background but it's not today's problem):
enter image description here
But if possible, I hope there is a way to achieve it, I would like the buttons to scale with window size.
So for example when the user resizes the window, I would like it to look somehow ike this (not exactly, but something similar):enter image description here
So as you can see I would like the button width and height getting changed, as the user resizes the window (and keeping their ratio within the window).
I hope there is a way to solve this problem.
Thank you for the help in advance.
I tried to right click on QWidget and then clicking on the last option (might be Alignment in English, I am not native) and then clicking on that option (Maybe align as Grid in English)
enter image description here
After doing this, the layout this expanded to the window size, the button got resized as well.
enter image description here
enter image description here
But the button width corresponds to the layout size (not just for example 1/3 of it as I would like) and the height does not change that greatly, just the width.
Premise: there are various questions on the matter here on StackOverflow; while they mostly point out to documentation or answer to specific issues, I've not found a comprehensive answer that could be considered as a "main reference" which can be used as duplicate pointer yet, especially when the developer wants to have big margins and leave some empty space within the UI. The following may be considered as a generic answer thanks to the simple nature of this question.
You are on the right track: layout managers are the solution, and while it's not forbidden to use explicit geometries, that practice its frowned upon[1].
Layout management basics
Know more about layout managers
Qt provides 2 basic layout types:
QBoxLayout, a "direction based" layout, that aligns widget along a specified direction: horizontally or vertically; Qt provides two convenience classes for those directions: respectively, QHBoxLayout and QVBoxLayout;
QGridLayout, a layout that aligns widget using a grid, similarly to a table or a spreadsheet;
There are also more complex layout managers:
form layout (QFormLayout), providing a simple "form style" layout, normally shown with a label on the left, and some widget on the right, with "items" shown from the top to the bottom;
stacked layout (QStackedLayout), which instead switches between visible widgets as they were "pages" (see below);
Additionally, there are complex widgets that implement custom layouts on their own:
QTabWidget is based on the convenience QStackedWidget class (using the above mentioned QStackedLayout) with the addition of a tab bar to allow the user to switch between them;
QSplitter, that can split the available space horizontally or vertically, with handles that allow resizing the contents within the available area;
QToolBox that behaves similarly to QTabWidget, with the difference that the "pages" are put in a column, similarly to a file cabinet;
Finally, in Qt, layout managers use layout items, which are abstract object that represent physical geometries that are being shown on the screen. Those items may be widgets, spacers or even nested layouts.
In this answer, I will only cover the basic (grid and boxed) layout managers.
Set a main layout
The first step is to ensure that the parent widget (the one that contains a group of child widgets) has a layout manager: in Designer (as the documentation explains), you have to open the context menu of the "container widget" by right clicking on an empty area inside it, and choose an appropriate item in the "Lay out" submenu.
Using code, that's normally done like this:
widget = QWidget()
layout = QVBoxLayout()
widget.setLayout(layout)
# alternatively, just use the target widget as argument in the constructor
# layout = QVBoxLayout(widget)
# the above line automatically calls setLayout(widget) internally
# ...
layout.addWidget(someWidget)
The issue of "responsiveness" and spacing
Modern UIs may often have lots of free space with relatively small controls. For instance, a login interface takes some amount of screen space, even if its input fields are quite small, allowing some space to show a fancy background or, even, just to better capture attention from the user.
With nowadays devices, we normally have a lot of available (and actually readable) screen size, but that wasn't the case until 10-20 years ago, when it was still normal to have "big" screens with a very small resolution (19" CRT screens only showing 1280x960 pixels if not less... heck, that's one of my screens!): you had about 90-100 pixels for inch, while High DPI screens or modern mobile devices can show about 10 times more in the same size. Less resolution means that it's more difficult to distinguish objects on the screen, especially when dealing with text; it's like having some light form of visual impairment: you may still be able to read text and set shapes apart, but it's difficult, you need to be more focused on what you're trying to see, and after some time that can be annoying and create fatigue.
The QtWidget module, similarly to other namespaces of other "old" common toolkits (eg. Gtk), was born on those concepts, meaning that "widgets" (UI elements that are used as human interface) have some requirements based on the available pixels, also considering the capabilities of the system to show text.
Long story short: widgets normally take as much space as it's possible in order to show their context, based on the principles above, but also considering previous, existing conventions.
Some widgets use space weirdly
Let's create two buttons and manually set their geometries:
And then set a vertical layout as explained above:
As you can see, they take all the available horizontal space, but do not extend vertically. The previous convention says that buttons do not expand vertically.
In the early days, UIs were simple: there were few buttons that were normally shown at the bottom of some dialog, and they used as much horizontal space as possible. Screen resolutions were actually small (640x480, or even less when using simple ASCII characters to display UI elements), there was no point in having "big" buttons, not to mention tall buttons.
Other widgets require different space usage
Let's add a QLineEdit to the top of the above layout: QLineEdit is a simple input field, it normally requires a simple string consisting of a single line; meaning that there is no point in requiring more vertical space, so the result is quite the same:
Now, we need a more complex text input, allowing text that may have multiple lines; let's add a QTextEdit widget:
Whoa, what's happened? Since QTextEdit is normally capable of showing multiple lines, it's important to take all the available space. Since the other widgets don't really need all that space, it will take advantage of it.
Size hints and policies
Layout managers have to decide how to set the geometry (position and size) of all the items they manage. In order to do that, they query all the items they manage (consider that layouts may be nested) and ask them about their size hints (the size that the item prefers), their constraints (minimum/maximum or fixed size) and their policy.
All Qt widgets provide a size policy, which tells the layout that manages them how they could be eventually resized and positioned. QPushButton has a fixed vertical policy (meaning that they usually have a predefined fixed height[2], as shown in the second image), while all scroll areas have an expanding vertical and horizontal policy, so they will try to take advantage of all the available space (and the layout will decide how much, based on all the other items).
Stretch factors
Basic layout managers support stretch factors, which can also be used as spacers: each layout item has a stretch factor that is considered as a ratio (computed with the total sum of all stretch factors of the layout).
Consider the following layout, using 2 QTextEdits:
Now, select the container widget in Designer, and scroll to the bottom of the Property Editor until we get the container layout properties; change the layoutStretch property to 1, 2, meaning that the available vertical space will be split in 3, with the first QTextEdit using the result of that value, and the second using twice (height / sum_of_stretches * stretch_of_item):
Margins and spaces
Considering the above, we still want to have a fancy UI that uses a lot of the huge available resolution and show very tiny widgets.
QBoxLayout classes provide the helper functions addStretch() and insertStretch(), that allow to create "empty" spaces (using QSpacerItem objects). This can also be done in Designer, by dragging and dropping the "Horizontal" or "Vertical" spacer item from the widget box; in the following image, I've added a vertical spacer to the top, and changed again the layoutStretch property to 1, 1, 2, meaning that there will be an empty space on top that is tall as much as the first QTextEdit, and both will be half of the second:
Complex layout management
As said above, QLayout subclasses manage their items, including nested layouts[3]. Let's restart from the basic two buttons and add spacers above and below:
That's still not fine. Let's set stretch factors properly; for instance, let the buttons take 1/5 of the available space each, with 2/5 of the space above and a remaining fifth below:
But that still doesn't work as expected. Remember about the size policy explained above. That property can be changed also in Designer (or by code by using setSizePolicy()); select those buttons and change their vertical policies to Preferred [4]:
That's better. But still not close enough: there's still a lot of unnecessarily used horizontal space.
We could change the maximumWidth properties of those buttons, but that would be fixed; we don't like that: the buttons will always have the same width, even if the window is very wide.
Enter QGridLayout
One of the benefits (and falls) of QGridLayout is that it always has a static amount of rows and columns [5], even if no layout item exists at that row/column cell position. This means that we can use its setRowStretch() and setColumnStretch() functions even when the layout has no widget for such row or column amount.
In Designer, we can change the layout type to a grid by right clicking on an empty area of the container, then it's just a matter of setting proper stretch factors, but if you already had a layout set it's better to select the Break Layout item and manually set an hypothetical layout by hand, then select Grid Layout from the submenu.
Let's restart again from scratch, as shown in the first image; break the layout and reposition/resize the buttons:
Then select a grid layout from the context menu (the following shows buttons for which a Preferred vertical size policy was already set):
Now add horizontal and vertical spacers:
Assuming that the vertical size policy of those buttons is set to Preferred as explained above, finally update the parent layout's layoutRowStretch and layoutColumnStretch factors to 2, 1, 1, 1 and 1, 1, 1 respectively; the vertical space will be split in 5, with an empty area occupying twice the resulting value, while the buttons and the bottom spacer occupying that fifth each; horizontally, left and right spacers will be as wide as the buttons:
If we resize the form or its preview, the button sizes are more responsive:
Note that in order to do that by code you must previously consider cell positions: the buttons will be added to rows 1 and 2, and column 1, then you have to properly call setRowStretch() and setColumnStretch() with appropriate indexes and factors.
This is one of the reasons for which QGridLayout may not always be the proper choice, especially for dynamic layouts for which the row/column cell count might not be known at first.
Layout management seems difficult, is it required?
The simple answer is "no", but reality is quite more complex.
As mentioned above, widgets must always ensure that they are always visible and usable. Modern systems use HighDPI screens, meaning that the physical pixels are never the same as logical pixels: a line that has a width of 1 "pixel" may actually be 10 pixels wide. Text may also depend on the font scaling.
Some visually impaired users (including people just having "simple" presbyopia) may set up their computers to have high font scale ratios (150, 200 or even more) in order to be able to read text more easily; some people may just use a peculiar default font that, at the default size, requires much more space to be shown, vertically and/or horizontally. Since Qt always tries to fully show a widget containing text considering the required space of its font, the result is that you may have overlapping widgets, because you didn't consider that another widget on its left or top may require more space than you thought.
The rule of thumb is: what you see on your device(s) is never what others will see.
Qt layout management (including QStyle functions, specifically those related to QSize such as QStyle.sizeFromContents()) always consider these factors, and, besides some unexpected behavior/bug, you can normally expect a resulting UI that is properly shown to the user.
99.9% of the times somebody wants to use fixed geometries, they are doing something wrong: they are probably trying to do something for the wrong reason (normally, lack of experience), and, in any case, they are not considering the above aspects.
As a reference, you've probably browsed some website on a mobile device that is simply "not responsive": you have to scroll a lot, and navigation is really annoying. That is because those website obviously didn't consider modern devices; and that's as annoying as a "not layout managed" UI might look. Luckily, even if the QtWidgets module is "old", it considers these modern aspects, and, even considering some glitches and inconsistencies, it normally allows proper geometry management as long as layout managers are properly used.
[1]: there is theoretically nothing wrong in explicitly setting geometries, as long as it's done with awareness; 99% of the times, it isn't: object require a certain size in order to be properly shown and used, which requires being aware of system settings: most importantly screen DPI and font scaling; Qt is quite careful about these aspects and tries to ensure that all widgets are properly displayed and usable; if you're getting issues with font or widget display, avoiding layout managers is not the solution;
[2]: Qt uses QStyle functions to decide how wide or tall a widget should or could be, based on the detected system configuration; you should normally trust it;
[3]: See the following posts: 1, 2 and 3;
[4]: It's possible to set properties to multiple widgets at once, as long as those properties are common; since the sizePolicy property is common to all widgets, we can select both buttons (using Ctrl) and the property change will be applied to both of them;
[5]: See this related post;
I have a layout question for python with qt5.
So, there is a main window with a normal vertical layout with 2 widgets.
The first one is a widget with a scrollarea which has a minimumSize & maximumSize set.
The second one is another widget with yet another scrollarea widget.
My goal is this. I load some content in the first widget and depending on the content it should either shrink or grow to the set min/max sizes and if it gets bigger than maxsize the scrollarea should take effect.
The second widget should always take all the rest of the available space.
I've tried all kinds of sizePolicy combinations but can't get it to quite to work. The second widget has a sizePolicy of Prefered/Prefered with vertical stretch set to 1, so it takes all the available space for itself.
The 1st widget has a miniumSize of 100 and a maximumSize of 250. So ideally it should shrink to something between 100-250 if the content is less and it should grow to 250 and activate the scrollbar if the content is getting bigger.
If I update the content of widget one (i.e. by clicking on a button) it should 1. resize/shrink/grow so the content fits, but not smaller than 100 and not larger than 250. If I have less content I should not be able to make widget one reszie to 250 - it shoudl always just take the exact needed height.
Any idea on how to do that?
example layout
Your scrollarea isn't going to change size, because it's a scrollarea. It doesn't need to size itself to its content, because the size of the contents of a scrollarea is basically unbounded. You can just scroll more. If you want to change the size of the first scrollarea, you're going to have to set its height manually.
Is there a way to set a fixed width of a QHBoxLayout?
For example, when I have two small widgets in it that take up little space and I don't want the two to split over the entire screen width when I full screen the app. The widgets already have their widths set to their minimumSizeHint() widths.
Just add a stretchable space to the end of the layout:
hbox_layout.addStretch()
Or if you want the widgets on the right:
hbox_layout.insertStretch(0)
Admission: I don't use PyQT, but I use Qt in C++. I believe it would work the same.
The trick here, is to as you run QHBoxLayout::addWidget(), you define a stretch factor (greater than zero) to the widgets you want to stretch. You define a zero-stretch factor (the default) to the ones you want to stay small.
Have you run QWidget::setMaximumWidth() on the smallish widgets? That would also be useful, perhaps.