qt-creator/doc/pluginhowto/first-plugin.qdoc

/*!
\page first-plugin.html
    itle 2. First Plugin
The best way to learn about writing Qt Creator plugins is to actually start by writing the very first plugin.

There are two ways for writing plugins for Qt Creator:
\list
\o \l {Writing plugin inside the source tree.}
\o \l {Writing plugin outside the source tree.}
\endlist
For Writing plugin in the any of the above mentioned way Qt Creator source scould have been compiled.

Lets keep our goals very simple for this one. We are going to provide a plugin for Qt Creator that does nothing. The purpose behind
this "Do nothing" plugin is to discover the basic classes in Qt Creator and to feel happy when our plugin shows up in the
"plugin list"

\inlineimage qtc-aboutplugin-2.png


    arget {Writing plugin inside the source tree.}
\section1 2.1 Create a plugin project in Qt Creator
Create a folder called DoNothing in $$QT_CREATOR_ROOT/src/plugins directory. The entire source code of
the plugin will be put into this directory.

\bold {Note:}\underline {It may be possible to write and build Qt Creator plugins outside of its source tree, but it is
much easier to write plugins within the source tree}.


Lets first create the \c {DoNothing.pro} file with the following contents
\code
TEMPLATE = lib
TARGET = DoNothing

PROVIDER = FooCompanyInc

include(../../qtcreatorplugin.pri)
include(../../plugins/coreplugin/coreplugin.pri)

HEADERS += DoNothingPlugin.h
SOURCES += DoNothingPlugin.cpp
OTHER_FILES += DoNothing.pluginspec
\endcode

The project file configures the following aspects of the plugin:
\list 1
\o Declares that DoNothing is a library. The output will be DoNothing.dll
\o Configures DoNothing to make use of settings defined in qtcreatorplugin.pri
\o Overrides the default destination directory to $$IDE_PLUGIN_PATH/FooCompanyInc. By default the value 
   will be to $$IDE_PLUGIN_PATH/Nokia
\o Configures DoNothing to make use of settings defined in coreplugin.pri
\o Provides information about the .h and .cpp files that make up the plugin
\endlist

\section1 2.2 Marking the plugin for build
Edit the \c {$$QT_CREATOR_ROOT/src/plugins/plugins.pro } file and include the following lines at the end of
the file and save the changes.

\code
SUBDIRS += plugin_DoNothing
plugin_DoNothing.subdir = DoNothing
\endcode

The above lines make sure that the next time we build Qt Creator, the DoNothing plugin is compiled along with the rest
of Qt Creator plugins.

\section1 2.3 Implementing the plugin
So far we have only written the project file and marked our plugin for compilation. We now do the actual
implementation of the plugin. All plugins implement the IPlugin interface. Lets take a look at how the DoNothing plugin
implements the interface and understand it in stages.

In \c {$$QT_CREATOR_ROOT/src/plugins/DoNothing/DoNothingPluigin.h} enter the following code.
\code
#ifndef DONOTHINGPLUGIN_H
#define DONOTHINGPLUGIN_H
#include <extensionsystem/iplugin.h>

class DoNothingPlugin : public ExtensionSystem::IPlugin
{
public:
    DoNothingPlugin();
    ~DoNothingPlugin();
    void extensionsInitialized();
    bool initialize(const QStringList & arguments, QString * errorString);
    void shutdown();
};
#endif // DONOTHINGPLUGIN_H
\endcode

As you can see the DoNothingPlugin class implements the IPlugin interface and nothing else. Lets look at how the
functions are implemented.

\code
#include "DoNothingPlugin.h"
#include <QtPlugin>
#include <QStringList>

DoNothingPlugin::DoNothingPlugin()
{
    // Do nothing
}

DoNothingPlugin::~DoNothingPlugin()
{
    // Do notning
}   
\endcode
Apart from initializing local (non widget and non action) variables; the constructor and destructor don't do much else.
\code

bool DoNothingPlugin::initialize(const QStringList& args, QString *errMsg)
{
    Q_UNUSED(args);
    Q_UNUSED(errMsg);
    return true;
}
\endcode

The \bold initialize() method is called when Qt Creator wants the plugin to initialize itself. This function is ideally used to
initialize the internal state of the plugin and register actions/objects with Qt Creator. The function is called after all the
dependencies of this plugin have been loaded.

Since our plugin really does nothing, we return \bold {true} signifying that the initialization was successful. If the initialization
was unsuccessful (for some wired reason); the \bold {errMsg} string should be set to a human readable error message.


\code
void DoNothingPlugin::extensionsInitialized()
{
    // Do nothing
}
\endcode

The \bold extensionsInitialized() method is called after this plugin has been initialized (ie. after initialize() method has been
called). This method is called on plugins that depend on this plugin first.
\code
void DoNothingPlugin::shutdown()
{
    // Do nothing
}
\endcode
The \bold shutdown() method is called when the plugin is about to be unloaded.
\code
Q_EXPORT_PLUGIN(DoNothingPlugin)
\endcode
Finally we export the plugin class by making use of the \bold {Q_EXPORT_PLUGIN()} macro.

\section1 2.4 Writing the pluginspec file

Each plugin should accompany a pluginspec file that provides some meta data about the plugin. For our plugin the
pluginspec file is as follows
\code
<plugin name="DoNothing" version="0.0.1">
    <vendor>FooCompanyInc</vendor>
    <copyright>(C) 2009-2011 FooCompanyInc Pvt. Ltd.</copyright>
    <license>Do anything you want</license>
    <description>A plugin that does nothing</description>
    <url>http://www.FooCompanyInc.com</url>
    <dependencyList>
        <dependency name="Core"/>
    </dependencyList>
</plugin>
\endcode
The pluginspec file provides the following fields of information:

\list 1
\o Name of the plugin, which is also used as the name of the library file that provides the plugin implementation.
  (In our case DoNothing.dll on Windows, libDoNothing.so on Unix)

\o Version of the plugin

\o Vendor name

\o Copyright

\o License text

\o Description

\o URL of the plugin vendor

\o Dependency List provides all the plugins that this plugin depends on. Qt Creator ensures that dependencies
   are loaded and initialized before this plugin.

\endlist

\bold {Note:}\underline {The pluginspec file should be in the same directory as the plugin's project file. Just to make things clear, the
contents of the DoNothing plugin directory is as shown below}


\inlineimage qtc-plugindirectory-2.png


\section1 2.5 Compiling the plugin

Open a command prompt and move to the Qt Creator build directory (the same build directory you created in the
previous chapter). Execute the following commands
\code
qmake ..\qtcreator.pro -recursive
nmake
\endcode
After nmake returns, you will notice a FooCompanyInc folder within plugins folder whose contents are shown in the image
below.

\inlineimage qtc-compiledplugin-2.png


\section1 2.6 Check out the new plugin
Launch (or relaunch) Qt Creator and notice that the "Installed Plugins" dialog box now reports that DoNothing plugin
was infact loaded and initialized.


\inlineimage qtc-installedplugin-2.png


In the coming chapters we will learn to write more complicated plugins for Qt Creator.

    arget {Writing plugin outside the source tree.}
\section1 2.7 Building out-of-source plugins

Thus far we have understood how to build plugins within the source tree of Qt Creator. It may not be practical for us to
use the Qt Creator source tree for plugin development all the time. Suppose that you are the author of a specialized
library (or application) and you want integrate your product into Qt Creator. Since you are a 3rd party developer you
cannot expect to have your code in Qt Creator source tree all the time. In this section we will look at how to build
plugins that are outside the Qt Creator source tree.

\section2 2.7.1 The plugin project file

The whole magic of out-of-source plugin builds lies in the project (.pro) file of your plugin. Lets the DoNothing plugin
discussed in the previous section and modify (its ".pro" file) so that plugins can be built from a directory outside Qt
Creator source.

The following table lists out the directory structure

\table
\header
\o Description
\o Directory

 \row 
 \o   Qt Creator Source Code 
 \o   C:\\Work\\QtCreator 

 \row
 \o Qt Creator Build Directory 
 \o C:\\Work\\QtCreator\\build

 \row
 \o DoNothing Plugin Source 
 \o C:\\Work\\Research\\QtCreator\\Plugins\\DoNothing


    This directory currently contains
    \list
    \o DoNothing.pluginspec
    \o DoNothing.pro
    \o DoNothingPlugin.cpp
    \o DoNothingPlugin.h
    \endlist
\row 
\o Target plugin directory
\o C:\\Work\\QtCreator\\build\\lib\\qtcreator\\plugins\\FooCompanyInc   

 \endtable

Let's now modify the DoNothing.pro file in C:\\Work\\Research\\QtCreator\\Plugins\\DoNothing as follows.

\code
QTC_SOURCE = C:/Work/QtCreator/
QTC_BUILD = C:/Work/QtCreator/build/

TEMPLATE = lib
TARGET = DoNothing

IDE_SOURCE_TREE = $$QTC_SOURCE
IDE_BUILD_TREE = $$QTC_BUILD

PROVIDER = FooCompanyInc

LIBS += -L$$IDE_PLUGIN_PATH/Nokia

include($$QTC_SOURCE/src/qtcreatorplugin.pri)
include($$QTC_SOURCE/src/plugins/coreplugin/coreplugin.pri)

HEADERS = DoNothingPlugin.h
SOURCES = DoNothingPlugin.cpp
OTHER_FILES = DoNothingPlugin.pluginspec
\endcode

The \bold{QTC_SOURCE} and \bold {QTC_BUILD} variables in the project file point to the source and build directories of Qt Creator.
If you prefer setting these as environment variables, then use \bold{$$(QTC_BUILD)} instead of \bold{$$QTC_BUILD} in the
project file.

The \bold {IDE_SOURCE_TREE} and \bold {IDE_BUILD_TREE} variables are used by qtcreatorplugin.pri to establish the include
and library paths.

The \bold {PROVIDER} and \bold {DESTDIR} directories must be set before including qtcreatorplugin.pri. This is because the variables
will be provided default values are \bold {Nokia} and \bold {$$IDE_BUILD_TREE/lib/qtcreator/plugins/Nokia} otherwise.

By default qtcreatorplugin.pri assumes that all the libs that a plugin may depend on are present inside the \bold {DESTDIR}. If
our \bold {DESTDIR} is different from the default (Nokia) one, then we will need to explicitly set that. The remaining things are
just the same.


\section2 2.7.2 Compiling the plugin

Once the project file has been created, we make use of the standard qmake and make commands to compile the plugin.

\code
C:\Work\Research\QtCreator\Plugins\DoNothing>qmake
C:\Work\Research\QtCreator\Plugins\DoNothing>nmake

Microsoft (R) Program Maintenance Utility Version 8.00.50727.762
Copyright (C) Microsoft Corporation. All rights reserved.

"C:\Program Files\Microsoft Visual Studio 8\VC\BIN\nmake.exe" -f Makefile.Debug
Microsoft (R) Program Maintenance Utility Version 8.00.50727.762
Copyright (C) Microsoft Corporation. All rights reserved.

copy /y "DoNothing.pluginspec"
"..\..\..\..\QtCreator\build\lib\qtcreator\plugins\FooCompanyInc\DoNothing.pluginspec"
1 file(s) copied.
........................................
mt.exe -nologo -manifest "debug\DoNothingd.intermediate.manifest" -
outputresource:..\..\..\..\QtCreator\build\lib\qtcreator\plugins\FooCompanyInc\DoNothingd.dll;2
C:\Work\Research\QtCreator\Plugins\DoNothing>
\endcode    
*/