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/*!
\page qtqml-modules-qmldir.html
\title Module Definition qmldir Files
\brief How to write a qmldir file which defines a QML module

There are two distinct types of \c qmldir files:
\list
\li QML document directory listing files
\li QML module definition files
\endlist

This documentation covers only the second form of \c qmldir file.  For more
information about the first form of \c qmldir file, please see the
documentation about
\l{qtqml-syntax-directoryimports.html#directory-listing-qmldir-files}
{directory listing qmldir files}.

\section1 Contents of a Module Definition qmldir File

A \c qmldir file which defines a module is a plain-text file which consists
of the following commands:

\table
    \header
        \li Command
        \li Syntax
        \li Usage

    \row
        \li Module Identifier Directive
        \li
            \code
module <ModuleIdentifier>
            \endcode
        \li Declares the module identifier of the module.
            The <ModuleIdentifier> is the (dotted URI notation) identifier
            for the module, which must match the module's install path.

            The \l{qtqml-modules-topic.html#the-module-identifier-directive}
            {module identifier directive} must be the first line of the file.
            Exactly one module identifier directive may exist in the \c qmldir
            file.

            Example:
            \code
module ExampleModule
            \endcode

    \row
        \li Object Type Declaration
        \li
            \code
<TypeName> <InitialVersion> <File>
            \endcode
        \li Declares a \l{qtqml-typesystem-objecttypes.html}{QML object type}
            to be made available by the module.
                \list
                \li \c <TypeName> is the type being made available
                \li \c <InitialVersion> is the module version for which the type is to be made available
                \li \c <File> is the (relative) file name of the QML file that defines the type
                \endlist

            Zero or more object type declarations may exist in the \c qmldir
            file, however each object type must have a unique type name within
            any particular version of the module.

            Example:
            \code
MyCustomType 1.0 MyCustomType.qml
            \endcode

    \row
        \li Internal Object Type Declaration
        \li
            \code
internal <TypeName> <File>
            \endcode
        \li Declares an object type that is in the module but should not be
            made available to users of the module.

            Zero or more internal object type declarations may exist in the
            \c qmldir file.

            Example:
            \code
internal MyPrivateType MyPrivateType.qml
         \endcode

            This is necessary if the module may be imported remotely (see
            \l{Remotely Installed Modules}) because if an exported type depends
            on an non-exported type within the module, the engine must also
            load the non-exported type.

    \row
        \li JavaScript Resource Declaration
        \li
            \code
<ResourceIdentifier> <InitialVersion> <File>
            \endcode
        \li Declares a JavaScript file to be made available by the module.
            The resource will be made available via the specified identifier
            with the specified version number.

            Zero or more JavaScript resource declarations may exist in the
            \c qmldir file, however each JavaScript resource must have a unique
            identifier within any particular version of the module.

            Example:
            \code
MyScript 1.0 MyScript.js
            \endcode

            See the documentation about \l{qtqml-javascript-resources.html}
            {defining JavaScript resources} and
            \l{qtqml-javascript-imports.html}
            {Importing JavaScript Resources In QML} for more information.

    \row
        \li C++ Plugin Declaration
        \li
            \code
plugin <Name> [<Path>]
            \endcode
        \li Declares a plugin to be made available by the module.

            \list
            \li \c <Name> is the plugin library name. This is usually not the
                same as the file name of the plugin binary, which is platform
                dependent; e.g. the library \c MyAppTypes would produce
                \c libMyAppTypes.so on Linux and \c MyAppTypes.dll on Windows.
            \li \c <Path> (optional) specifes either:
                \list
                \li an absolute path to the directory containing the plugin
                    file, or
                \li a relative path from the directory containing the \c qmldir
                    file to the directory containing the plugin file.
                \endlist

                By default the engine searches for the plugin library in the
                directory that contains the \c qmldir file. (The plugin search
                path can be queried with QQmlEngine::pluginPathList() and
                modified using QQmlEngine::addPluginPath().)
            \endlist

            Zero or more C++ plugin declarations may exist in the \c qmldir
            file, however since plugin loading is a relatively expensive
            operation, clients are advised to specify at most a single plugin.

            Example:
            \code
plugin MyPluginLibrary
           \endcode

    \row
        \li Type Information Description File Declaration
        \li
            \code
typeinfo <File>
            \endcode
        \li Declares a \l{Writing a qmltypes file}{type description file} for
            the module that can be read by QML tools such as Qt Creator to
            access information about the types defined by the module's plugins.
            \c <File> is the (relative) file name of a \c .qmltypes file.

            Example:
            \code
typeinfo mymodule.qmltypes
            \endcode

            Without such a file, QML tools may be unable to offer features such
            as code completion for the types defined in your plugins.

    \row
        \li Comment
        \li
            \code
# <Comment>
            \endcode
        \li Declares a comment. These are ignored by the engine.

            Example:
            \code
# this is a comment
            \endcode
\endtable

Each command in a \c qmldir file must be on a separate line.

\section1 Versioning Semantics

Types which are exported for a particular version are still made available if a
later version is imported.  If a module provides a \c MyButton type in version
1.0 and a \c MyWindow type in version 1.1, clients which import version 1.1 of
the module will be able to use the \c MyButton type and the \c MyWindow type.
However, the reverse is not true: a type exported for a particular version
cannot be used if an earlier version is imported. If the client had imported
version 1.0 of the module, they can use the \c MyButton type but \b not the
\c MyWindow type.

A type can be defined by different files in different versions. In this case,
the most closely matching version will be used when imported by clients.
For example, if a module had specified the following types via its \c qmldir
file:

\code
module ExampleModule
MyButton 1.0 MyButton.qml
MyButton 1.1 MyButton11.qml
MyButton 1.3 MyButton13.qml
MyButton 2.0 MyButton20.qml
MyRectangle 1.2 MyRectangle12.qml
\endcode

a client who imports version 1.2 of ExampleModule will get the \c MyButton
type definition provided by \c MyButton11.qml as it is the most closely
matching (i.e., latest while not being greater than the import) version of the
type, and the \c MyRectangle type definition provided by \c MyRectangle12.qml.

The versioning system ensures that a given QML file will work regardless of the
version of installed software, since a versioned import \e only imports types
for that version, leaving other identifiers available, even if the actual
installed version might otherwise provide those identifiers.

See \l{examples/qml/plugins} for an example that uses C++
plugins.


\section1 Example of a qmldir File

One example of a \c qmldir file follows:

\code
module ExampleModule
CustomButton 1.0 CustomButton.qml
CustomButton 2.0 CustomButton20.qml
CustomButton 2.1 CustomButton21.qml
plugin examplemodule
MathFunctions 2.0 mathfuncs.js
\endcode

The above \c qmldir file defines a module called "ExampleModule".  It defines
the \c CustomButton QML object type in versions 1.1, 2.0 and 2.1 of the
module, with different implementations in each version.  It specifies a plugin
which must be loaded by the engine when the module is imported by clients, and
that plugin may register various C++-defined types with the QML type system.
On Unix-like systems the QML engine will attempt to load \c libexamplemodule.so
as a QQmlExtensionPlugin, and on Windows it will attempt to load
\c examplemodule.dll as a QQmlExtensionPlugin.  Finally, the \c qmldir file
specifies a \l{qtqml-javascript-resources.html}{JavaScript resource} which is
only available if version 2.0 or greater of the module is imported, accessible
via the \c MathFunctions identifier.

If the module is \l{qtqml-modules-identifiedmodules.html}{installed} into the
QML import path, clients could import and use the module in the following
manner:

\qml
import QtQuick 2.0
import ExampleModule 2.1

Rectangle {
    width: 400
    height: 400
    color: "lightsteelblue"

    CustomButton {
        color: "gray"
        text: "Click Me!"
        onClicked: MathFunctions.generateRandom() > 10 ? color = "red" : color = "gray";
    }
}
\endqml

The \c CustomButton type used above would come from the definition specified in
the \c CustomButton21.qml file, and the JavaScript resource identified by the
\c MathFunctions identifier would be defined in the \c mathfuncs.js file.


\section1 Writing a qmltypes File

QML modules may refer to one or more type information files in their
\c qmldir file. These usually have the \c .qmltypes
extension and are read by external tools to gain information about
types defined in plugins.

As such qmltypes files have no effect on the functionality of a QML module.
Their only use is to allow tools such as Qt Creator to provide code completion,
error checking and other functionality to users of your module.

Any module that uses plugins should also ship a type description file.

The best way to create a qmltypes file for your module is to generate it
using the \c qmlplugindump tool that is provided with Qt.

Example:
If your module is in \c /tmp/imports/My/Module, you could run
\code
qmlplugindump My.Module 1.0 /tmp/imports > /tmp/imports/My/Module/mymodule.qmltypes
\endcode
to generate type information for your module. Afterwards, add the line
\code
typeinfo mymodule.qmltypes
\endcode
to \c /tmp/imports/My/Module/qmldir to register it.

While the qmldump tool covers most cases, it does not work if:
\list
\li The plugin uses a \c{QQmlCustomParser}. The component that uses
   the custom parser will not get its members documented.
\li The plugin can not be loaded. In particular if you cross-compiled
   the plugin for a different architecture, qmldump will not be able to
   load it.
\endlist

In case you have to create a qmltypes file manually or need to adjust
an existing one, this is the file format:

\qml
import QtQuick.tooling 1.1

// There always is a single Module object that contains all
// Component objects.
Module {
    // A Component object directly corresponds to a type exported
    // in a plugin with a call to qmlRegisterType.
    Component {

        // The name is a unique identifier used to refer to this type.
        // It is recommended you simply use the C++ type name.
        name: "QQuickAbstractAnimation"

        // The name of the prototype Component.
        prototype: "QObject"

        // The name of the default property.
        defaultProperty: "animations"

        // The name of the type containing attached properties
        // and methods.
        attachedType: "QDeclarativeAnimationAttached"

        // The list of exports determines how a type can be imported.
        // Each string has the format "URI/Name version" and matches the
        // arguments to qmlRegisterType. Usually types are only exported
        // once, if at all.
        // If the "URI/" part of the string is missing that means the
        // type should be put into the package defined by the URI the
        // module was imported with.
        // For example if this module was imported with 'import Foo 4.8'
        // the Animation object would be found in the package Foo and
        // QtQuick.
        exports: [
            "Animation 4.7",
            "QtQuick/Animation 1.0"
        ]

        // The meta object revisions for the exports specified in 'exports'.
        // Describes with revisioned properties will be visible in an export.
        // The list must have exactly the same length as the 'exports' list.
        // For example the 'animations' propery described below will only be
        // available through the QtQuick/Animation 1.0 export.
        exportMetaObjectRevisions: [0, 1]

        Property {
            name: "animations";
            type: "QQuickAbstractAnimation"
            // defaults to false, whether this property is read only
            isReadonly: true
            // defaults to false, whether the type of this property was a pointer in C++
            isPointer: true
            // defaults to false: whether the type actually is a QQmlListProperty<type>
            isList: true
            // defaults to 0: the meta object revision that introduced this property
            revision: 1
        }
        Property { name: "loops"; type: "int" }
        Property { name: "name"; type: "string" }
        Property { name: "loopsEnum"; type: "Loops" }

        Enum {
            name: "Loops"
            values: {
                "Infinite": -2,
                "OnceOnly": 1
            }
        }

        // Signal and Method work the same way. The inner Parameter
        // declarations also support the isReadonly, isPointer and isList
        // attributes which mean the same as for Property
        Method { name: "restart" }
        Signal { name: "started"; revision: 2 }
        Signal {
            name: "runningChanged"
            Parameter { type: "bool" }
            Parameter { name: "foo"; type: "bool" }
        }
    }
}
\endqml

*/

