Differences between Qt Quick Controls 1

Qt Quick Controls 1 was originally developed to support desktop platforms, with mobile and embedded support coming shortly afterwards. They have a very broad scope, in that they provide a styling system flexible enough to allow the development of applications that have either a platform-dependent or platform-independent style.

On embedded systems, where the hardware has limited resources, this approach can be inefficient. Qt Quick Controls 2 was designed to solve this problem, using benchmarks to guide the development.

C++ and QML

In many cases, the internal state of a control can be more efficiently processed in C++. For example, handling input events in C++ makes a difference for controls that would otherwise need to create internal MouseAreas and attached Keys objects.

Styles

Not only does handling events and logic in C++ increase performance, but it allows the visual QML layer to be a simple, declarative layer on top. This is reflected in the structure of the controls project: all visual implementations sit in the imports folder, so that users who want to create their own complete style can copy the folder and start tweaking. Read more about implementing a style plugin here.

In Qt Quick Controls 2, styles no longer provide components that are dynamically instantiated by controls, but controls themselves consist of item delegates that can be replaced. In effect, this means that delegates are Qt Quick items that are instantiated on the spot, as properties of the control, and are simply parented to the control.

Modularity and Simplicity

When it comes to more complex controls, it is sometimes better to split them up into separate building blocks. As an example, the complex ScrollView control:

ScrollView {
    horizontalScrollBarPolicy: Qt.ScrollBarAlwaysOff
    Flickable {
        // ...
    }
}

Is replaced with simple ScrollBar/ScrollIndicator controls that can be attached to any Flickable:

Flickable {
    // ...
    ScrollBar.vertical: ScrollBar { }
}

The API of Qt Quick Controls 2 aims to be clean and simple. Common operations are easy, and more advanced ones are liberally documented with snippets that can be copied into your code.

Feature Comparison Table

	Qt Quick Controls 1	Qt Quick Controls 2
Stylable delegates	Yes	Yes
Pre-built native styles	Yes	No
Runtime style/theme changes	Yes ¹	Yes ²
Can be used on Desktop	Yes	Yes
Can be used on Mobile	Yes ³	Yes
Can be used on Embedded	Yes ³	Yes
Internal event handling	QML	C++

Not officially supported, but technically possible via private APIs
Only themes for specific styles can be changed at runtime, styles are fixed
Performance may not be optimal

Porting Qt Quick Controls 1 Code

The API of Qt Quick Controls 2 is very similar to Qt Quick Controls 1, but it does come with some changes necessary to facilitate the improvements. The majority of changes are to do with styling; all of a control's delegates are now accessible in the control itself, instead of in a separate style object.

For example, to style a button in Qt Quick Controls 1:

Button {
    style: ButtonStyle {
        label: Label {
            // ...
        }
    }
}

To style a button in Qt Quick Controls 2:

Button {
    contentItem: Label {
        // ...
    }
}

Preparing for Migration

With this in mind, a good way to prepare for a migration to Qt Quick Controls 2 is to place each control that you have a custom style for in its own QML file. For example, the Qt Quick Controls 1 button above could be moved to a file named Button.qml in a directory named controls, and used in the following manner:

import "controls" as Controls

Controls.Button {
    // ...
}

This works with both modules, and will reduce the amount of work needed when the migration begins.

Type Comparison Table

The first column lists all types available in Qt Quick Controls 1, Qt Quick Dialogs, and Qt Quick Extras. The second column documents the respective type in Qt Quick Controls 2. When a direct alternative is not available, the third column contains an alternative that provides related functionality. The last column contains some remarks about the differences between the types in the different modules.

Qt Quick Controls 1	Qt Quick Controls 2	Alternatives	Remarks
Action	Action	Shortcut ^{(Qt Quick)}
ApplicationWindow	ApplicationWindow
BusyIndicator	BusyIndicator
Button	Button
Calendar	—	MonthGrid, DayOfWeekRow, WeekNumberColumn ^{(Qt Labs Calendar)}	Qt Labs Calendar: `MonthGrid`, `DayOfWeek`, and `WeekNumberColumn` are experimental unstyled building blocks for calendar views.
CheckBox	CheckBox
ComboBox	ComboBox
ExclusiveGroup	—	ActionGroup, ButtonGroup ^{(Qt Quick Controls 2)}	Qt Quick Controls 2: `ActionGroup` and `ButtonGroup` offer similar functionality.
GroupBox	GroupBox
Label	Label
Menu	Menu	Menu ^{(Qt Labs Platform)}	Qt Quick Controls 1: `Menu` is native on platforms where an implementation is available in the Qt Platform Abstraction Layer. Other platforms use a QML-based top-level menu popup window. `Menu` supports traditional desktop style cascading submenus, but does not work on Embedded Linux because EGLFS does not support multiple top-level windows. Qt Quick Controls 2: `Menu` is a non-native `Item-based` popup that is stacked above the application content. Due to this, menu popups are restricted within window boundaries. `Menu` is fully customizable using QML and Qt Quick, and allows adding any `Items`. Traditional desktop oriented features, such as cascading submenus and visualizing keyboard shortcuts are missing. Qt Labs Platform: `Menu` is an experimental native menu that uses Qt Widgets as a fallback on platforms where a native implementation is not available in the Qt Platform Abstraction Layer.
MenuBar	MenuBar	MenuBar ^{(Qt Labs Platform)}	Qt Quick Controls 1: `MenuBar` is native on platforms where an implementation is available in the Qt Platform Abstraction Layer. Other platforms use a QML-based menubar item stacked at the top of the window. Qt Quick Controls 2: `MenuBar` is a non-native QML-based menubar that can be fully customized using QML and Qt Quick. Qt Labs Platform: `MenuBar` is an experimental native menubar. It is only available on platforms where a native implementation is available in the Qt Platform Abstraction Layer.
MenuItem, MenuSeparator	MenuItem, MenuSeparator	MenuItem, MenuSeparator ^{(Qt Labs Platform)}	Qt Quick Controls 1: `MenuItem` and `MenuSeparator` are native on platforms where an implementation is available in the Qt Platform Abstraction Layer. Other platforms use QML-based menu items and separators. Qt Quick Controls 2: `MenuItem` and `MenuSeparator` are a non-native QML-based menu items and separators that can be fully customized using QML and Qt Quick. Qt Labs Platform: `MenuItem` and `MenuSeparator` are experimental native menu items and separators.
ProgressBar	ProgressBar
RadioButton	RadioButton
ScrollView	ScrollView
Slider	Slider
SpinBox	SpinBox
SplitView	—
StackView, StackViewDelegate, Stack	StackView		Qt Quick Controls 2: `StackView` provides customizable transitions and attached properties via a single `StackView` type.
StatusBar	—	ToolBar ^{(Qt Quick Controls 2)}	Qt Quick Controls 2: `ApplicationWindow` allows assigning any item or control, such as `ToolBar`, as a header or footer.
Switch	Switch
TabView, Tab	—	TabBar, TabButton ^{(Qt Quick Controls 2)}	Qt Quick Controls 2: `TabBar` and `TabButton` offer similar functionality, and can be used to build tabbed views.
TableView	—
TextArea	TextArea		Qt Quick Controls 1: `TextArea` inherits `ScrollView` and is therefore always a scrollable editor. Qt Quick Controls 2: `TextArea` is a simpler multi-line editor that can be optionally attached to a `Flickable` to provide scrolling functionality. This allows using `TextArea` in a scrollable page without having two nested scrollable areas, which can be problematic and cause usability issues.
TextField	TextField
ToolBar	ToolBar
ToolButton	ToolButton
TreeView	—
Qt Quick Dialogs	Qt Quick Controls 2	Alternatives	Remarks
Dialog	—	Dialog	Qt Quick Dialogs: `Dialog` is either a top-level window or an `Item-based` popup depending on whether the underlying platform supports multiple top-level windows. Qt Quick Controls 2: `Dialog` is not a top-level window, but an `Item-based` popup that is stacked above the application content. Due to this, dialogs are restricted within window boundaries.
ColorDialog, FileDialog, FontDialog, MessageDialog	—	ColorDialog, FileDialog, FolderDialog, FontDialog, MessageDialog ^{(Qt Labs Platform)}	Qt Quick Dialogs: Dialogs are native on platforms where an implementation is available in the Qt Platform Abstraction Layer. Other platforms use either Qt Widgets or QML-based dialogs depending on whether the underlying platform supports multiple top-level windows. Qt Labs Platform: Experimental native dialogs that use Qt Widgets as a fallback on platforms where a native implementation is not available in the Qt Platform Abstraction Layer.
Qt Quick Extras	Qt Quick Controls 2	Alternatives	Remarks
CircularGauge	—
DelayButton	DelayButton
Dial	Dial
Gauge	—
Picture	—
PieMenu	—
StatusIndicator	—
ToggleButton	—
Tumbler, TumblerColumn	Tumbler		Qt Quick Extras: `Tumbler` can consist of multiple columns. Qt Quick Controls 2: `Tumbler` presents a single spinnable wheel. Multiple columns can be created by placing multiple `Tumblers` next to each other.
No Predecessor	Qt Quick Controls 2	Alternatives	Remarks
—	AbstractButton
—	ActionGroup	ExclusiveGroup ^{(Qt Quick Controls 1)}	Qt Quick Controls 1: `ExclusiveGroup` offers similar functionality.
—	ButtonGroup	ExclusiveGroup ^{(Qt Quick Controls 1)}	Qt Quick Controls 1: `ExclusiveGroup` offers similar functionality.
—	CheckDelegate
—	Container
—	Control
—	Drawer
—	Frame
—	ItemDelegate
—	Page
—	PageIndicator
—	Pane
—	Popup
—	RadioDelegate
—	RangeSlider
—	RoundButton
—	ScrollBar, ScrollIndicator	ScrollView ^{(Qt Quick Controls 1)}	Qt Quick Controls 1: `ScrollView` offers similar functionality. It combines horizontal and vertical scrollbars, and the background and frame around the scrollable view.
—	—	StandardPaths ^{(Qt Labs Platform)}	Qt Quick Dialogs: `FileDialog` offers a shortcut property that can be used to access the most common standard paths. Qt Labs Platform: `StandardPaths` offers a separate type to give full access to the standard paths.
—	SwipeDelegate
—	SwipeView
—	SwitchDelegate
—	—	SystemTrayIcon ^{(Qt Labs Platform)}	Qt Labs Platform: `SystemTrayIcon` is an experimental native system tray icon that uses Qt Widgets as a fallback on platforms where a native implementation is not available in the Qt Platform Abstraction Layer.
—	TabBar, TabButton	TabView ^{(Qt Quick Controls 1)}	Qt Quick Controls 1: `TabView` offers similar functionality. It combines the tab bar, background and frame around the tabs.
—	ToolSeparator
—	ToolTip		Qt Quick Controls 1: `Button` and `Action` have built-in Qt Widgets-based tooltips. Qt Quick Controls 2: `ToolTip` can be attached to any `Item`.

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https://doc.qt.io/qt-5.12/qtquickcontrols2-differences.html