qtdoc/doc/src/qmlapp/codingconventions.qdoc

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/*!
\page qml-codingconventions.html
\title QML Coding Conventions
\brief code style convention

This document contains the QML coding conventions that we follow in our documentation and examples and recommend that others follow.

\section1 QML Object Declarations

Throughout our documentation and examples, \l{QML Object Attributes}{QML object attributes} are always structured in the following order:

\list
\li id
\li property declarations
\li signal declarations
\li JavaScript functions
\li object properties
\li child objects
\endlist

For better readability, we separate these different parts with an empty line.


For example, a hypothetical \e photo QML object would look like this:

\snippet qmlapp/codingconventions/photo.qml 0


\section1 Grouped Properties

If using multiple properties from a group of properties,
consider using \e {group notation} instead of \e {dot notation} if it
improves readability.

For example, this:

\snippet qmlapp/codingconventions/dotproperties.qml 0

could be written like this:

\snippet qmlapp/codingconventions/dotproperties.qml 1

\section1 Unqualified access

In order to improve readability and performance always reference properties of parent components by their id explicitly:

\snippet qmlapp/codingconventions/qualifiedaccess.qml 0

\section1 Required properties

When requiring data defined outside the component, make this explicit by using \l{Required Properties}.
Required properties must be set or else the creation of the component will fail.
These are preferable to unqualified lookups because they are more performant and allow for both
users and tooling to reason about an external property's type.
Additionally they remove assumptions that a component otherwise has to make about the environment
in which it is created.

\section1 Signal handlers

When handling parameters in signal handlers use functions which name them explicitly:

\snippet qmlapp/codingconventions/signalhandler.qml 0

\section1 JavaScript Code

If the script is a single expression, we recommend writing it inline:

\snippet qmlapp/codingconventions/javascript.qml 0

If the script is only a couple of lines long, we generally use a block:

\snippet qmlapp/codingconventions/javascript.qml 1

If the script is more than a couple of lines long or can be used by different objects, we recommend creating a function and calling it like this:

\snippet qmlapp/codingconventions/javascript.qml 2

Also note that is recommended to add type annotations to your function in order
to more easily reason about and refactor your application since both parameter
and return types are immediately visible from the function signature.

For long scripts, we will put the functions in their own JavaScript file and import it like this:

\snippet qmlapp/codingconventions/javascript-imports.qml 0

If the code is longer than one line and hence within a block,
we use semicolons to indicate the end of each statement:

\snippet qmlapp/codingconventions/javascript-semicolons.qml 0

\section1 Related Information

\list
    \li \l {Best Practices for QML and Qt Quick}
\endlist

*/