Qt 5.7 | Qt Quick Controls 2 | Differences between Qt Quick Controls

Qt 5.7.1 Reference Documentation

# Differences between Qt Quick Controls

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

* No hover effects

### Porting Qt Quick Controls Code

The API of Qt Quick Controls 2 is very similar to Qt Quick Controls, 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:

      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 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

Qt Quick Controls 1, Qt Quick Extras | Qt Quick Controls 2, Qt Labs Calendar
--- | ---
— | AbstractButton
Action | — (see Shortcut instead)
ApplicationWindow | ApplicationWindow
BusyIndicator | BusyIndicator
Button | Button
CircularGauge | —
— | Control
— | Container
Calendar | MonthGrid, DayOfWeekRow, WeekNumberColumn
CheckBox | CheckBox
— | CheckDelegate
ComboBox | ComboBox
DelayButton | —
Dial | Dial
— | Drawer
ExclusiveGroup | ButtonGroup
— | Frame
Gauge | —
GroupBox | GroupBox
— | ItemDelegate
Label | Label
Menu | Menu
MenuBar | —
MenuItem | MenuItem
— | Page
— | PageIndicator
— | Pane
Picture | —
PieMenu | —
— | Popup
ProgressBar | ProgressBar
RadioButton | RadioButton
— | RadioDelegate
— | RangeSlider
ScrollView | ScrollBar, ScrollIndicator
Slider | Slider
SplitView | —
SpinBox | SpinBox
StackView, StackViewDelegate, Stack | StackView
StatusBar | —
StatusIndicator | —
— | SwipeDelegate
— | SwipeView
Switch | Switch
— | SwitchDelegate
TabView, Tab | TabBar, TabButton
TableView | —
TextArea | TextArea
TextField | TextField
ToggleButton | —
ToolBar | ToolBar
ToolButton | ToolButton
— | ToolTip
TreeView | —
Tumbler, TumblerColumn | Tumbler

## Related Information

- Qt Quick
- Qt Quick Controls 2 QML Types
- Qt Quick Controls QML Types
- Qt Quick Extras QML Types