Qt 5.6 | Qt Labs Controls | Differences between Qt Quick Controls

Qt 5.6.3 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 Labs Controls 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 Labs Controls, 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 Labs Controls 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 Labs Controls
--- | --- | ---
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 support

### Porting Qt Quick Controls Code

The API of Qt Labs Controls 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 Labs Controls:

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

#### Preparing for Migration

With this in mind, a good way to prepare for a migration to Qt Quick Labs 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, 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 Changes

Qt Quick Controls | Qt Labs Controls
--- | ---
Action | No equivalent; see Shortcut instead.
ApplicationWindow | ApplicationWindow
BusyIndicator | BusyIndicator
Button | Button
Calendar | No equivalent; see MonthGrid, DayOfWeekRow and WeekNumberColumn instead.
CheckBox | CheckBox
ComboBox | ComboBox
ExclusiveGroup | ButtonGroup
GroupBox | GroupBox, or Frame if a title is not required.
Label | Label
Menu | Menu
ProgressBar | ProgressBar
RadioButton | RadioButton
ScrollView | ScrollBar, ScrollIndicator
Slider | Slider
SpinBox | SpinBox
Stack, StackView, StackViewDelegate | StackView
StatusBar | No equivalent
Switch | Switch
Tab, TabView | TabBar in combination with, for example, SwipeView.
TableView | No equivalent
TextArea | TextArea
TextField | TextField
ToolBar | ToolBar
ToolButton | ToolButton
TreeView | No equivalent

## Related Information

- Qt Quick
- Qt Quick Controls
- Qt Labs Controls QML Types