Settings QML Type

Provides persistent platform-independent application settings. More...

• List of all members, including inherited members

Properties

• category : string
• location : url

Methods

• setValue(string key, var value)
• sync()
• var value(string key, var defaultValue)

Detailed Description

The Settings type provides persistent platform-independent application settings.

Users normally expect an application to remember its settings (window sizes and positions, options, etc.) across sessions. The Settings type enables you to save and restore such application settings with the minimum of effort.

Individual setting values are specified by declaring properties within a Settings element. Only value types recognized by QSettings are supported. The recommended approach is to use property aliases in order to get automatic property updates both ways. The following example shows how to use Settings to store and restore the geometry of a window.

 import QtCore
 import QtQuick

 Window {
     id: window

     width: 800
     height: 600

     Settings {
         property alias x: window.x
         property alias y: window.y
         property alias width: window.width
         property alias height: window.height
     }
 }

At first application startup, the window gets default dimensions specified as 800x600. Notice that no default position is specified - we let the window manager handle that. Later when the window geometry changes, new values will be automatically stored to the persistent settings. The second application run will get initial values from the persistent settings, bringing the window back to the previous position and size.

A fully declarative syntax, achieved by using property aliases, comes at the cost of storing persistent settings whenever the values of aliased properties change. Normal properties can be used to gain more fine-grained control over storing the persistent settings. The following example illustrates how to save a setting on component destruction.

 import QtCore
 import QtQuick

 Item {
     id: page

     state: settings.state

     states: [
         State {
             name: "active"
             // ...
         },
         State {
             name: "inactive"
             // ...
         }
     ]

     Settings {
         id: settings
         property string state: "active"
     }

     Component.onDestruction: {
         settings.state = page.state
     }
 }

Notice how the default value is now specified in the persistent setting property, and the actual property is bound to the setting in order to get the initial value from the persistent settings.

Application Identifiers

Application specific settings are identified by providing application name, organization and domain, or by specifying location.

 #include <QGuiApplication>
 #include <QQmlApplicationEngine>

 int main(int argc, char *argv[])
 {
     QGuiApplication app(argc, argv);
     app.setOrganizationName("Some Company");
     app.setOrganizationDomain("somecompany.com");
     app.setApplicationName("Amazing Application");

     QQmlApplicationEngine engine("main.qml");
     return app.exec();
 }

These are typically specified in C++ in the beginning of main(), but can also be controlled in QML via the following properties:

• Qt.application.name,
• Qt.application.organization and
• Qt.application.domain.

Categories

Application settings may be divided into logical categories by specifying a category name via the category property. Using logical categories not only provides a cleaner settings structure, but also prevents possible conflicts between setting keys.

If several categories are required, use several Settings objects, each with their own category:

 Item {
     id: panel

     visible: true

     Settings {
         category: "OutputPanel"
         property alias visible: panel.visible
         // ...
     }

     Settings {
         category: "General"
         property alias fontSize: fontSizeSpinBox.value
         // ...
     }
 }

Instead of ensuring that all settings in the application have unique names, the settings can be divided into unique categories that may then contain settings using the same names that are used in other categories - without a conflict.

Settings singleton

It's often useful to have settings available to every QML file as a singleton. For an example of this, see the To Do List example. Specifically, AppSettings.qml is the singleton, and in the CMakeLists.txt file, the QT_QML_SINGLETON_TYPE property is set to TRUE for that file via set_source_files_properties.

Notes

The current implementation is based on QSettings. This imposes certain limitations, such as missing change notifications. Writing a setting value using one instance of Settings does not update the value in another Settings instance, even if they are referring to the same setting in the same category.

The information is stored in the system registry on Windows, and in XML preferences files on macOS. On other Unix systems, in the absence of a standard, INI text files are used. See QSettings documentation for more details.

See also QSettings.

Property Documentation

Method Documentation