Qt Quick Best Practices

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This article lists out the best practices and also the DOs and DONTs recommended by developers while developing with Qt Quick. Please add your recommendations and help this page grow …

Formatting

/**
 * The example component accomplishes …
 */

Rectangle {
id: example

    // size independently from screen height
    width: 100
    height: 100
}

Use 4 spaces for indentation

  • Let the { bracket be on the same line separated by 1 white space
  • Use blank lines intelligently to separate code blocks
  • Use a blank line before a multi line comment - easy to read

Basics

  • Starting Qt 4.7.1, use QtQuick namespace, import QtQuick 1.0 - more consistent and is aimed for backward compatibility
  • The .qml file name should start with an uppercase letter
  • Use property alias and avoid duplicating same property within a component - uses less memory
  • Specify each property in a single line - helps readability
  • If you are grouping multiple properties in a single line - group logically related properties (e.g. x, y makes sense. x, color are not related)
  • Use Grouped Properties where you find logical group of properties (e.g. font)
  • Property names should begin with a lowercase letter (exception being Attached Properties)
  • Use square brackets even while assigning a single property to a list - easy to identify that its a list
  • Define signal handlers with the prefix "on" (e.g. onHover)
  • Avoid single line comment at the end of line - one can easily miss this
  • Avoid over documentation, name your variables meaningfully

Mandatory

  • Each .qml file should have only one top level component
  • Each .qml file should have at least one import
  • Component name should match the .qml file
  • A component id will be unique in that .qml file
  • The component id must not be enclosed within quotes
  • The component id must begin with a lower-case letter or underscore
  • The component id cannot contain characters other than letters, numbers and underscores
  • Specify property and value with this syntax property: value
  • Multiple properties on same line are separated by a semicolon

Best Practices

  • Avoid hard coding of sizes and positions, use layouts smartly
  • Use QML more for UI and let Qt/C++ handle the backend, i.e. the business logic, data models
  • Trying to do too much in javascript will lead to performance issues, use Qt C++
  • Use javascript as sparingly as possible
  • Expose the current state and the state change as properties rather than functions - cleaner integration with QML property binding
  • Keep C++ implementation agnostic of the QML user interface implementation and the QML object tree composition
  • Avoid directly manipulating the QML object tree using C++. QML elements should "pull" data from C++ rather than C++ trying to "push" data into QML elements
  • Use OpenGL to do any blending, scaling or rotating. (-opengl to qmlviewer or QGLWidget as viewport of QDeclarativeView)
  • Run fullscreen rather than maximized to avoid compositing overhead (-fullscreen to qmlviewer or use showFullscreen() rather than show())

Open for discussion- add your comments directly here

  • Default Property: If a property has been declared as the default property, the property tag can be omitted. Is this a good idea?
  • Use single line comment at the end of line only in places like end of a code block Is commenting ends of block this a good style?
  • If a single property has to be documented, an end of line comment could still be used

For common coding conventions have also a look on http://doc.qt.io/qt-5/qml-codingconventions.html

see also