directoryimports.qdoc

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// Copyright (C) 2017 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\page qtqml-syntax-directoryimports.html
\title Importing QML Document Directories
\brief Description of directory import statements in QML
 
A local directory of QML files can be imported without any additional setup or
configuration.  A remote directory of QML files can also be imported, but
requires a directory listing \c qmldir file to exist.  A local directory may
optionally contain a directory listing \c qmldir file in order to define the
type names which should be provided to clients which import the directory, and
to specify JavaScript resources which should be made available to importers.
 
Qt assumes that all files inside the imported directory come from a trusted source.
 
\section1 Local Directory Imports
 
Any QML file on the local file system can import a local directory as using an
import statement that refers to the directory's absolute or relative file
system path, enabling the file to use the \l{qtqml-typesystem-objecttypes.html}
{object types} defined within that directory.
 
The QML runtime reads an optional directory listing \c qmldir file from the
imported directory to discover available types defined in QML and C++. The
\c qmldir file specifies the names of the types defined in QML and the paths
of the plugins containing C++ defined types.
 
QML files are made available with the type names specified in the \c qmldir file
if there is one; otherwise, they will be made available with type names derived
from the filenames of the QML documents. Only filenames beginning with an
uppercase letter and ending with ".qml" will be exposed as types if no \c qmldir
file is specified in the directory.
 
The QML runtime loads all plugins listed in the \c qmldir file to find
all types exposed from C++.
 
Directory Imports rank below any
\l{qtqml-modules-identifiedmodules.html}{module imports} in precedence. If the
same name is defined in a module and in a directory that are both imported into
the same namespace, only the module's type is made available.
 
\section2 An Example
 
Consider the following QML project directory structure. Under the top level directory \c myapp,
there are a set of common UI components in a sub-directory named \c mycomponents, and the main
application code in a sub-directory named \c main, like this:
 
\code
myapp
    |- mycomponents
        |- CheckBox.qml
        |- DialogBox.qml
        |- Slider.qml
    |- main
        |- application.qml
\endcode
 
The \c main/application.qml file can import the \c mycomponents directory using
the relative path to that directory, allowing it to use the QML object types
defined within that directory:
 
\qml
import "../mycomponents"
 
DialogBox {
    CheckBox {
        // ...
    }
    Slider {
        // ...
    }
}
\endqml
 
The directory may be imported into a qualified local namespace, in which case
uses of any types provided in the directory must be qualified:
 
\qml
import "../mycomponents" as MyComponents
 
MyComponents.DialogBox {
    // ...
}
\endqml
 
The ability to import a local directory is convenient for cases such as
in-application component sets and application prototyping, although any code
that imports such modules must update their relevant \c import statements
if the module directory moves to another location.  This can be avoided if
\l{qtqml-modules-identifiedmodules.html}{QML modules} are used instead,
as an installed module is imported with a unique identifier string rather than
a file system path.
 
 
\section1 The Implicit Import
 
The directory a QML document resides in is automatically imported. You do
not have to explicitly import \c{"."} or similar.
 
\note You should make sure that the qmldir file that specifies the module a QML
document belongs to resides in the same directory as the QML document itself.
Otherwise the implicit import is different from the module the document belongs
to. Then, for example, another QML document may be a singleton in the context of
the module, but not a singleton in the context of the implicit import. This is a
frequent source of mistakes.
 
 
\section1 Remotely Located Directories
 
A directory of QML files can also be imported from a remote location if the
directory contains a directory listing \c qmldir file.
 
\note This also holds for the \l{The Implicit Import}{implicit import} of the
directory a QML document resides in. If your QML documents are loaded from a
remote location, you need to add qmldir files even if they don't contain any
explicit directory import statements. Otherwise your QML documents won't see
each other.
 
For example, if the \c myapp directory in the previous example was hosted at
"http://www.my-example-server.com", and the \c mycomponents directory
contained a \c qmldir file defined as follows:
 
\code
CheckBox CheckBox.qml
DialogBox DialogBox.qml
Slider Slider.qml
\endcode
 
Then, the directory could be imported using the URL to the remote
\c mycomponents directory:
 
\qml
import "http://www.my-example-server.com/myapp/mycomponents"
 
DialogBox {
    CheckBox {
        // ...
    }
    Slider {
        // ...
    }
}
\endqml
 
Note that when a file imports a directory over a network, it can only access QML
and JavaScript files specified in the \c qmldir file located in the directory.
 
\warning When importing directories from a remote server, developers should
always be careful to only load directories from trusted sources to avoid
loading malicious code.
 
 
\section1 Directory Listing qmldir Files
 
A directory listing \c qmldir file is distinctly different from a
\l{qtqml-modules-qmldir.html}{module definition qmldir file}.  A directory
listing \c qmldir file allows a group of QML documents to be quickly and easily
shared, but it does not define a type namespace into which the QML object types
defined by the documents are registered, nor does it support versioning of
those QML object types.
 
The syntax of a directory listing \c qmldir file is as follows:
\table
    \header
    \li Command
    \li Syntax
    \li Description
 
    \row
    \li Object Type Declaration
    \li <TypeName> <FileName>
    \li An object type declaration allows a QML document to be exposed with
        the given \c <TypeName>.
 
        Example:
        \code
RoundedButton RoundedBtn.qml
        \endcode
 
    \row
    \li Internal Object Type Declaration
    \li internal <TypeName> <FileName>
    \li An internal object type declaration allows a QML document to be
        registered as a type which becomes available only to the other
        QML documents contained in the directory import.  The internal
        type will not be made available to clients who import the directory.
 
        Example:
        \code
internal HighlightedButton HighlightedBtn.qml
        \endcode
 
    \row
    \li JavaScript Resource Declaration
    \li <Identifier> <FileName>
    \li A JavaScript resource declaration allows a JavaScript file to be
        exposed via the given identifier.
 
        Example:
        \code
MathFunctions mathfuncs.js
        \endcode
\endtable
 
A local file system directory may optionally include a \c qmldir file. This
allows the engine to only expose certain QML types to clients who import the
directory.  Additionally, JavaScript resources in the directory are not exposed
to clients unless they are declared in a \c qmldir file.
 
*/