path: root/doc/api/first-plugin.qdoc

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/*!
    \page first-plugin.html
    \title Creating Your First Plugin

    This section describes how to create a \QC plugin by using the plugin
    template provided by \QC, and get the first impression of what
    a plugin consists of and what its general structure is.

    \section1 Creating a Plugin Project

    \QC comes with a wizard for \QC plugins, that creates a
    runable, \e minimal plugin for you. We strongly suggest that you
    use two different \QC instances for developing and testing
    your plugin with. Otherwise your plugin will also be loaded in your
    development environment, which can make that unstable while your
    plugin is still unstable. You can just create a copy of your \QC
    build and use one for actually developing, and the other for testing
    your plugin with.

    \list 1
        \o Select \gui{File > New File or Project > Other Qt Project > Qt Creator Plugin > Choose}.

           \image firstplugin-wizard.png "Choose the \QC Plugin Wizard"

           The \gui{Introduction and Project Location} dialog opens.

           \image firstplugin-nameandpath.png "Choose Name and Place of the Project"

        \o Give your project a name and specify in which path
           this project will be created. The actual plugin's name can be different
           from the project name. You will choose that name later in the wizard.
           Continue to the next page.

           The \gui{Target Setup} dialog opens.

           \image firstplugin-target.png "Choose the Desktop Target and Matching Qt"

        \o Select the target and Qt version to build your project with.
           For a \QC plugin this needs to be the \gui{Desktop} target,
           and a Qt version that is compatible with the Qt version that your
           \QC was built with (in the best case the exact same build).
           If you use an incompatible Qt version to build your plugin, you
           will get errors while \QC tries to load your plugin.
           Continue to the next page.

           The \gui{Plugin Information} dialog opens.

           \image firstplugin-pluginsetup.png "Specify Your Plugin Details"

        \o In the \gui{Plugin name} field, type \gui{Example}. The name of the plugin
           is used as its identifier, and also is the base for the file names and
           classes in the code.

        \o The values of the following fields are mainly informational, and
           are shown in the detailed view in \QC's plugin overview
           (\gui{Help > About Plugins}, or \gui{Qt Creator > About Plugins}
           on Mac).

           \list
               \o \gui{Vendor name} is a short one-word name of the company
                  or organization that created the plugin. This is also used for
                  the path name where the plugin will be deployed to.
               \o \gui{Copyright} is a one-line, short copyright string.
               \o \gui{License} is a multi-line license text (but shouldn't be pages over pages long,
                  since the interface doesn't allow nice reading of long texts).
               \o \gui{Description} is a relatively short, but
                  possibly multi-line description of what the plugin does.
               \o \gui{URL} is a website where the user can find more
                  information about the plugin and/or organization providing it.
           \endlist

        \o Set the \gui{Qt Creator sources} and \gui{Qt Creator build} fields to
           the source and build directory of the \QC
           instance you want to use to test your plugin with, respectively.
           If you don't do that correctly you will get compile errors for your
           plugin, and your plugin might not show up in \QC at all.

        \o In the \gui{Deploy into} list, select \gui{Qt Creator build}. This sets
           your .pro file up to deploy your plugin directly into your \QC build's
           plugin directory (requires you to have write permissions there).
           The other option, \gui{Local user settings}, sets your .pro file up to
           deploy your plugin into \QC's user plugin path
           (for example \c{~/.config/Nokia/qtcreator/plugins} on Unix systems).
           We choose \gui{Qt Creator build} because we use a self-compiled
           \QC, and want the plugin to be only loaded by that \QC
           instance.
           Continue to the next page.

           The \gui{Project Management} dialog opens.

           \image firstplugin-summary.png "Summary of Created Files"

        \o Review the files that will be created, choose a version control
           system that \QC should use for your project (always a good idea!),
           and finish the wizard.
    \endlist

    \section1 Building and Running the Plugin

    If you passed the correct \QC source and build paths in the project
    wizard, your plugin should just build fine when pressing the build button.
    When you try to run your project, \QC will ask you for the executable to run and
    you are presented the following dialog:

    \image firstplugin-runsettings.png "Specify the Executable to Run"

    Select the path to the \QC executable from the build that you specified
    in the \gui{Qt Creator build} setting in the project wizard and click \gui OK.
    \QC starts up, and you can verify that your plugin successfully loaded
    by looking for a menu entry \gui{Tools > Example} and by looking for
    the plugin in the \gui{About Plugins} dialog.

    \image firstplugin-menuitem.png "Menu Registered by the Plugin"

    \section1 File Structure

    The plugin wizard creates a set of basic files that a plugin needs or should have.
    We will have a look at some of them in detail in the following sections, here is a short
    overview:

    \table
    \header
        \o File
        \o Role
    \row
        \o \c{Example.pluginspec.in}
        \o Template plugin specification. QMake creates a \c{Example.pluginspec}
           from this file, which is read by \QC to find out about the plugin.
    \row
        \o \c{example.pro}
        \o Project file, used by QMake to generate a Makefile that then is used to
           build the plugin.
    \row
        \o \c{example_global.h}
        \o Contains macro definitions that are useful when this plugin should export
           symbols to other plugins.
    \row
        \o \c{exampleconstants.h}
        \o Header defining constants used by the plugin code.
    \row
        \o \c{exampleplugin.h/.cpp}
        \o C++ header and source files that define the plugin class that will be
           instanciated and run by \QC's plugin manager.
    \endtable

    \section1 qmake Project

    The qmake project file \c{example.pro} defines how your plugin should be compiled.
    \QC plugins need to have a specific setup there, in addition to telling qmake
    which files need to be compiled (or handled by \c moc or \c uic).
    Let us have a look at what the project wizard generated for you in detail.

    \snippet exampleplugin/example.pro 1

    The first section of the .pro file defines the very basic properties of your project,
    the name (\c{TARGET}), and that a library should be generated,
    since plugins are actually libraries that are dynamically loaded (\c{TEMPLATE = lib}).
    The section also lets the compiler pass an \c EXAMPLE_LIBRARY define to the compiled
    code, which is used in the \c{example_global.h} header, but is not really of interest
    for now. You should not need to change that section of the .pro file.

    \snippet exampleplugin/example.pro 2

    This section tells qmake about the files of your project that it should let
    compile or otherwise handle. You need to expand that section with any files
    you add to the project.

    \snippet exampleplugin/example.pro 3

    To compile and deploy your plugin, the project needs access to the \QC sources and
    build. This section contains the logic that looks for the information about
    the location of the sources and build in the \c{QTC_SOURCE} and \c{QTC_BUILD}
    environment variables. If these are not defined, it uses the defaults you
    set in the project wizard.

    So, if someone else opens your plugin project on their machine, they do not
    need to edit the .pro file, but instead they should set the \c{QTC_SOURCE} and
    \c{QTC_BUILD} environment variables correctly for the plugin's build environment.

    You should not need to change this section, except perhaps to adapt the defaults.

    \snippet exampleplugin/example.pro 4

    \QC plugins can either be installed into the \QC installation's plugin directory
    (requires write access there), or to a user specific plugin directory.
    The \c USE_USER_DESTDIR switch in the .pro file defines which method is used for building
    the plugin (which is independent from what you can later use for distributing your
    plugin to other users).

    \snippet exampleplugin/example.pro 5

    The \c{PROVIDER} variable is for example used to deploy your plugin to a provider specific
    plugin subdirectory, and the value is taken from the information that
    you gave in the plugin project wizard.

    \snippet exampleplugin/example.pro 6

    This section includes the necessary parts from the \QC sources and makes your
    plugin find the \QC libraries and plugins. The included file
    \c{qtcreatorplugin.pri} makes sure that you build a plugin that is suitable
    for use in \QC. The file \c{plugins/coreplugin/coreplugin.pri} makes your
    plugin dependent on the Core plugin and makes sure that you can access its
    public API.
    If you want to use or extend functionality from other plugins, you
    need to add the corresponding .pri file of the plugin here.

    For more information about qmake, and writing .pro files in general,
    see the \l{http://doc.qt.nokia.com/4.7/qmake-manual.html}{qmake Manual}.

    \section1 Plugin Specification

    The .pluginspec file is an XML file that contains information that is needed by
    the plugin manager to find your plugin and resolve its dependencies before actually
    loading your plugin's library file. We will only have a short look at it here.
    For more information, see \l{Plugin Specifications}.

    The wizard doesn't actually create a .pluginspec file directly, but instead a
    .pluginspec.in file. qmake uses this to generate the actual plugin specification
    file, replacing variables like \c{QTCREATOR_VERSION} with their actual values.
    Therefore you need to escape all backslashes and quotes in the .pluginspec.in file
    (i.e. you need to write \c{\\} to get a backslash and \c{\"} to get a quote
    in the generated plugin specification).

    \snippet exampleplugin/Example.pluginspec.in 1

    The main tag of the plugin specification that is created by the wizard
    defines the name of your plugin, its version, and with what version of this plugin
    the current version is binary compatible with.

    \snippet exampleplugin/Example.pluginspec.in 2

    After the main tag you'll find the information about the plugin
    that you gave in the project wizard.

    \snippet exampleplugin/Example.pluginspec.in 3

    The last section tells the plugin manager about the dependencies of this
    plugin. Most \QC plugins will at least depend on the \c{Core} plugin.

    \section1 Plugin Class

    The files \c{exampleplugin.h} and \c{exampleplugin.cpp} define the plugin
    implementation of your little plugin. We'll concentrate on some highlights
    here, and give pointers to more detailed information for the various parts.

    \section2 Header File

    The header file \c{exampleplugin.h} defines the interface of the plugin class.

    \snippet exampleplugin/exampleplugin.h namespaces

    The plugin is defined in a \c{Example::Internal} namespace, which conforms to
    the coding rules for \l{coding-rules-namespacing}{namespacing}
    in \QC sources.

    \snippet exampleplugin/exampleplugin.h base class

    All \QC plugins must be derived from \l{ExtensionSystem::IPlugin} and
    are QObjects.

    \snippet exampleplugin/exampleplugin.h plugin methods

    The base class defines basic methods that are called during the life cycle
    of a plugin, which are here implemented for your new plugin.
    These methods and their roles are described in detail in
    \l{The Plugin Life Cycle}.

    \snippet exampleplugin/exampleplugin.h slot

    The plugin has an additional custom slot, that is used to pop up a dialog
    when the user chooses the menu item that this plugin adds.

    \section2 Source File

    The source file contains the actual implementation of the plugin, which registers
    a new menu and menu item, and opens a message box when that item is triggered.

    All the necessary header files from the plugin code itself,
    from the Core plugin, and from Qt are included in the beginning of the file.
    The setup of the menu and menu item
    is done in the plugin's \c{initialize} method, which is the first thing called
    after the plugin constructor. In that method, the plugin can be sure that the basic
    setup of plugin's that it depends on has been done, for example the Core plugin's
    \c{ActionManager} instance has been created.

    For more information about implementing the plugin interface, see the
    \l{ExtensionSystem::IPlugin} API documentation and \l{Plugin Life Cycle}.

    \snippet exampleplugin/exampleplugin.cpp add action

    This part of the code creates a new \c{QAction}, registers it as a new
    \c{Command} in the action manager, and connects it to the plugin's slot.
    The action manager provides a central place where the user can assign and
    change keyboard shortcuts, and manages cases where for example a menu item should be
    directed to different plugins under different circumstances, as well as a few
    other things. This is described in more detail in \l{Menus and Menu Items}.

    \snippet exampleplugin/exampleplugin.cpp add menu

    Here a new menu item is created, the created command added to it, and the menu
    added to the \gui{Tools} menu in the menu bar. Again, this is covered in more
    detail in \l{Menus and Menu Items}.

    \snippet exampleplugin/exampleplugin.cpp slot implementation

    This part defines the code that is called when the menu item is triggered.
    It uses the Qt API to open a message box that displays informative text and
    an \gui OK button.

    \snippet exampleplugin/exampleplugin.cpp export plugin

    At the end of the file, the Qt macro \c{Q_EXPORT_PLUGIN2} is used to register
    the plugin with Qt's plugin loader system. This is necessary for Qt to
    be able to load your plugin.

*/