.. only:: html .. index:: Plugins; Folder, Python; Developing plugins .. _structuring_plugins: ************************** Structuring Python Plugins ************************** .. contents:: :local: In order to create a plugin, here are some steps to follow: #. *Idea*: Have an idea about what you want to do with your new QGIS plugin. Why do you do it? What problem do you want to solve? Is there already another plugin for that problem? #. *Create files*: The essentials: a starting point :file:`__init__.py`; fill in the :ref:`plugin_metadata` :file:`metadata.txt`. Then implement your own design. A main Python plugin body e.g. :file:`mainplugin.py`. Probably a form in Qt Designer :file:`form.ui`, with its :file:`resources.qrc`. #. *Write code*: Write the code inside the :file:`mainplugin.py` #. *Test*: Close and re-open QGIS and import your plugin again. Check if everything is OK. #. *Publish*: Publish your plugin in QGIS repository or make your own repository as an "arsenal" of personal "GIS weapons". .. index:: Plugins; Writing Writing a plugin ================ Since the introduction of Python plugins in QGIS, a number of plugins have appeared. The QGIS team maintains an :ref:`official_pyqgis_repository`. You can use their source to learn more about programming with PyQGIS or find out whether you are duplicating development effort. .. _plugin_files_architecture: Plugin files ------------ Here's the directory structure of our example plugin :: PYTHON_PLUGINS_PATH/ MyPlugin/ __init__.py --> *required* mainPlugin.py --> *core code* metadata.txt --> *required* resources.qrc --> *likely useful* resources.py --> *compiled version, likely useful* form.ui --> *likely useful* form.py --> *compiled version, likely useful* What is the meaning of the files: * :file:`__init__.py` = The starting point of the plugin. It has to have the :func:`classFactory` method and may have any other initialisation code. * :file:`mainPlugin.py` = The main working code of the plugin. Contains all the information about the actions of the plugin and the main code. * :file:`resources.qrc` = The .xml document created by Qt Designer. Contains relative paths to resources of the forms. * :file:`resources.py` = The translation of the .qrc file described above to Python. * :file:`form.ui` = The GUI created by Qt Designer. * :file:`form.py` = The translation of the form.ui described above to Python. * :file:`metadata.txt` = Contains general info, version, name and some other metadata used by plugins website and plugin infrastructure. `Here `_ is an online automated way of creating the basic files (skeleton) of a typical QGIS Python plugin. There is a QGIS plugin called `Plugin Builder 3 `_ that creates a plugin template for QGIS and doesn't require an internet connection. This is the recommended option, as it produces 3.x compatible sources. .. warning:: If you plan to upload the plugin to the :ref:`official_pyqgis_repository` you must check that your plugin follows some additional rules, required for plugin :ref:`official_pyqgis_repository_validation` .. index:: Plugins; Writing code Plugin content ============== Here you can find information and examples about what to add in each of the files in the file structure described above. .. index:: Plugins; Metadata, metadata.txt .. _plugin_metadata: Plugin metadata --------------- First, the plugin manager needs to retrieve some basic information about the plugin such as its name, description etc. File :file:`metadata.txt` is the right place to put this information. .. note:: All metadata must be in UTF-8 encoding. .. _plugin_metadata_table: ===================== ======== ======================================= Metadata name Required Notes ===================== ======== ======================================= name True a short string containing the name of the plugin qgisMinimumVersion True dotted notation of minimum QGIS version qgisMaximumVersion False dotted notation of maximum QGIS version description True short text which describes the plugin, no HTML allowed about True longer text which describes the plugin in details, no HTML allowed version True short string with the version dotted notation author True author name email True email of the author, only shown on the website to logged in users, but visible in the Plugin Manager after the plugin is installed changelog False string, can be multiline, no HTML allowed experimental False boolean flag, `True` or `False` - `True` if this version is experimental deprecated False boolean flag, `True` or `False`, applies to the whole plugin and not just to the uploaded version tags False comma separated list, spaces are allowed inside individual tags homepage False a valid URL pointing to the homepage of your plugin repository True a valid URL for the source code repository tracker False a valid URL for tickets and bug reports icon False a file name or a relative path (relative to the base folder of the plugin's compressed package) of a web friendly image (PNG, JPEG) category False one of `Raster`, `Vector`, `Database` and `Web` plugin_dependencies False PIP-like comma separated list of other plugins to install server False boolean flag, `True` or `False`, determines if the plugin has a server interface hasProcessingProvider False boolean flag, `True` or `False`, determines if the plugin provides processing algorithms ===================== ======== ======================================= | By default, plugins are placed in the `Plugins` menu (we will see in the next section how to add a menu entry for your plugin) but they can also be placed the into :menuselection:`Raster`, :menuselection:`Vector`, :menuselection:`Database` and :menuselection:`Web` menus. A corresponding "category" metadata entry exists to specify that, so the plugin can be classified accordingly. This metadata entry is used as tip for users and tells them where (in which menu) the plugin can be found. Allowed values for "category" are: Vector, Raster, Database or Web. For example, if your plugin will be available from `Raster` menu, add this to :file:`metadata.txt` :: category=Raster .. note:: If `qgisMaximumVersion` is empty, it will be automatically set to the major version plus `.99` when uploaded to the :ref:`official_pyqgis_repository`. An example for this metadata.txt :: ; the next section is mandatory [general] name=HelloWorld email=me@example.com author=Just Me qgisMinimumVersion=3.0 description=This is an example plugin for greeting the world. Multiline is allowed: lines starting with spaces belong to the same field, in this case to the "description" field. HTML formatting is not allowed. about=This paragraph can contain a detailed description of the plugin. Multiline is allowed, HTML is not. version=version 1.2 tracker=http://bugs.itopen.it repository=http://www.itopen.it/repo ; end of mandatory metadata ; start of optional metadata category=Raster changelog=The changelog lists the plugin versions and their changes as in the example below: 1.0 - First stable release 0.9 - All features implemented 0.8 - First testing release ; Tags are in comma separated value format, spaces are allowed within the ; tag name. ; Tags should be in English language. Please also check for existing tags and ; synonyms before creating a new one. tags=wkt,raster,hello world ; these metadata can be empty, they will eventually become mandatory. homepage=https://www.itopen.it icon=icon.png ; experimental flag (applies to the single version) experimental=True ; deprecated flag (applies to the whole plugin and not only to the uploaded version) deprecated=False ; if empty, it will be automatically set to major version + .99 qgisMaximumVersion=3.99 .. index:: Plugins; Initialisation __init__.py ----------- This file is required by Python's import system. Also, QGIS requires that this file contains a :func:`classFactory()` function, which is called when the plugin gets loaded into QGIS. It receives a reference to the instance of :class:`QgisInterface ` and must return an object of your plugin's class from the :file:`mainplugin.py` --- in our case it's called ``TestPlugin`` (see below). This is how :file:`__init__.py` should look like :: def classFactory(iface): from .mainPlugin import TestPlugin return TestPlugin(iface) ## any other initialisation needed mainPlugin.py ------------- This is where the magic happens and this is how magic looks like: (e.g. :file:`mainPlugin.py`) :: from qgis.PyQt.QtGui import * from qgis.PyQt.QtWidgets import * # initialize Qt resources from file resources.py from . import resources class TestPlugin: def __init__(self, iface): # save reference to the QGIS interface self.iface = iface def initGui(self): # create action that will start plugin configuration self.action = QAction(QIcon(":/plugins/testplug/icon.png"), "Test plugin", self.iface.mainWindow()) self.action.setObjectName("testAction") self.action.setWhatsThis("Configuration for test plugin") self.action.setStatusTip("This is status tip") self.action.triggered.connect(self.run) # add toolbar button and menu item self.iface.addToolBarIcon(self.action) self.iface.addPluginToMenu("&Test plugins", self.action) # connect to signal renderComplete which is emitted when canvas # rendering is done self.iface.mapCanvas().renderComplete.connect(self.renderTest) def unload(self): # remove the plugin menu item and icon self.iface.removePluginMenu("&Test plugins", self.action) self.iface.removeToolBarIcon(self.action) # disconnect form signal of the canvas self.iface.mapCanvas().renderComplete.disconnect(self.renderTest) def run(self): # create and show a configuration dialog or something similar print("TestPlugin: run called!") def renderTest(self, painter): # use painter for drawing to map canvas print("TestPlugin: renderTest called!") The only plugin functions that must exist in the main plugin source file (e.g. :file:`mainPlugin.py`) are: * ``__init__`` --> which gives access to QGIS interface * ``initGui()`` --> called when the plugin is loaded * ``unload()`` --> called when the plugin is unloaded In the above example, :meth:`addPluginToMenu ` is used. This will add the corresponding menu action to the :menuselection:`Plugins` menu. Alternative methods exist to add the action to a different menu. Here is a list of those methods: * :meth:`addPluginToRasterMenu() ` * :meth:`addPluginToVectorMenu() ` * :meth:`addPluginToDatabaseMenu() ` * :meth:`addPluginToWebMenu() ` All of them have the same syntax as the :meth:`addPluginToMenu ` method. Adding your plugin menu to one of those predefined method is recommended to keep consistency in how plugin entries are organized. However, you can add your custom menu group directly to the menu bar, as the next example demonstrates: :: def initGui(self): self.menu = QMenu(self.iface.mainWindow()) self.menu.setObjectName("testMenu") self.menu.setTitle("MyMenu") self.action = QAction(QIcon(":/plugins/testplug/icon.png"), "Test plugin", self.iface.mainWindow()) self.action.setObjectName("testAction") self.action.setWhatsThis("Configuration for test plugin") self.action.setStatusTip("This is status tip") self.action.triggered.connect(self.run) self.menu.addAction(self.action) menuBar = self.iface.mainWindow().menuBar() menuBar.insertMenu(self.iface.firstRightStandardMenu().menuAction(), self.menu) def unload(self): self.menu.deleteLater() Don't forget to set :class:`QAction` and :class:`QMenu` ``objectName`` to a name specific to your plugin so that it can be customized. .. index:: Plugins; Resource file, resources.qrc Resource File ------------- You can see that in :func:`initGui()` we've used an icon from the resource file (called :file:`resources.qrc` in our case) :: icon.png It is good to use a prefix that will not collide with other plugins or any parts of QGIS, otherwise you might get resources you did not want. Now you just need to generate a Python file that will contain the resources. It's done with :command:`pyrcc5` command: :: pyrcc5 -o resources.py resources.qrc .. note:: In Windows environments, attempting to run the :command:`pyrcc5` from Command Prompt or Powershell will probably result in the error "Windows cannot access the specified device, path, or file [...]". The easiest solution is probably to use the OSGeo4W Shell but if you are comfortable modifying the PATH environment variable or specifiying the path to the executable explicitly you should be able to find it at :file:`\\bin\\pyrcc5.exe`. And that's all... nothing complicated :) If you've done everything correctly you should be able to find and load your plugin in the plugin manager and see a message in console when toolbar icon or appropriate menu item is selected. When working on a real plugin it's wise to write the plugin in another (working) directory and create a makefile which will generate UI + resource files and install the plugin into your QGIS installation. .. index:: Plugins; Documentation, Plugins; Implementing help Documentation ============= The documentation for the plugin can be written as HTML help files. The :mod:`qgis.utils` module provides a function, :func:`showPluginHelp` which will open the help file browser, in the same way as other QGIS help. The :func:`showPluginHelp` function looks for help files in the same directory as the calling module. It will look for, in turn, :file:`index-ll_cc.html`, :file:`index-ll.html`, :file:`index-en.html`, :file:`index-en_us.html` and :file:`index.html`, displaying whichever it finds first. Here ``ll_cc`` is the QGIS locale. This allows multiple translations of the documentation to be included with the plugin. The :func:`showPluginHelp` function can also take parameters packageName, which identifies a specific plugin for which the help will be displayed, filename, which can replace "index" in the names of files being searched, and section, which is the name of an html anchor tag in the document on which the browser will be positioned. .. index:: Plugins; Code snippets, Plugins; Translation Translation =========== With a few steps you can set up the environment for the plugin localization so that depending on the locale settings of your computer the plugin will be loaded in different languages. Software requirements --------------------- The easiest way to create and manage all the translation files is to install `Qt Linguist `_. In a Debian-based GNU/Linux environment you can install it typing:: sudo apt install qttools5-dev-tools Files and directory ------------------- When you create the plugin you will find the ``i18n`` folder within the main plugin directory. **All the translation files have to be within this directory.** .pro file ......... First you should create a ``.pro`` file, that is a *project* file that can be managed by **Qt Linguist**. In this ``.pro`` file you have to specify all the files and forms you want to translate. This file is used to set up the localization files and variables. A possible project file, matching the structure of our :ref:`example plugin `: :: FORMS = ../form.ui SOURCES = ../your_plugin.py TRANSLATIONS = your_plugin_it.ts Your plugin might follow a more complex structure, and it might be distributed across several files. If this is the case, keep in mind that ``pylupdate5``, the program we use to read the ``.pro`` file and update the translatable string, does not expand wild card characters, so you need to place every file explicitly in the ``.pro`` file. Your project file might then look like something like this: :: FORMS = ../ui/about.ui ../ui/feedback.ui \ ../ui/main_dialog.ui SOURCES = ../your_plugin.py ../computation.py \ ../utils.py Furthermore, the ``your_plugin.py`` file is the file that *calls* all the menu and sub-menus of your plugin in the QGIS toolbar and you want to translate them all. Finally with the *TRANSLATIONS* variable you can specify the translation languages you want. .. warning:: Be sure to name the ``ts`` file like ``your_plugin_`` + ``language`` + ``.ts`` otherwise the language loading will fail! Use the 2 letter shortcut for the language (**it** for Italian, **de** for German, etc...) .ts file ........ Once you have created the ``.pro`` you are ready to generate the ``.ts`` file(s) for the language(s) of your plugin. Open a terminal, go to ``your_plugin/i18n`` directory and type:: pylupdate5 your_plugin.pro you should see the ``your_plugin_language.ts`` file(s). Open the ``.ts`` file with **Qt Linguist** and start to translate. .qm file ........ When you finish to translate your plugin (if some strings are not completed the source language for those strings will be used) you have to create the ``.qm`` file (the compiled ``.ts`` file that will be used by QGIS). Just open a terminal cd in ``your_plugin/i18n`` directory and type:: lrelease your_plugin.ts now, in the ``i18n`` directory you will see the ``your_plugin.qm`` file(s). Translate using Makefile ------------------------- Alternatively you can use the makefile to extract messages from python code and Qt dialogs, if you created your plugin with Plugin Builder. At the beginning of the Makefile there is a LOCALES variable:: LOCALES = en Add the abbreviation of the language to this variable, for example for Hungarian language:: LOCALES = en hu Now you can generate or update the :file:`hu.ts` file (and the :file:`en.ts` too) from the sources by:: make transup After this, you have updated ``.ts`` file for all languages set in the LOCALES variable. Use **Qt Linguist** to translate the program messages. Finishing the translation the ``.qm`` files can be created by the transcompile:: make transcompile You have to distribute ``.ts`` files with your plugin. Load the plugin --------------- In order to see the translation of your plugin just open QGIS, change the language (:menuselection:`Settings --> Options --> Language`) and restart QGIS. You should see your plugin in the correct language. .. warning:: If you change something in your plugin (new UIs, new menu, etc..) you have to **generate again** the update version of both ``.ts`` and ``.qm`` file, so run again the command of above. Tips and Tricks =============== Plugin Reloader --------------- During development of your plugin you will frequently need to reload it in QGIS for testing. This is very easy using the Plugin Reloader plugin. You can find it as an experimental plugin with the Plugin Manager. Accessing Plugins ----------------- You can access all the classes of installed plugins from within QGIS using python, which can be handy for debugging purposes.:: my_plugin = qgis.utils.plugins['My Plugin'] Log Messages ------------ Plugins have their own tab within the :ref:`log_message_panel`. Share your plugin ----------------- QGIS is hosting hundreds of plugins in the plugin repository. Consider sharing yours! It will extend the possibilities of QGIS and people will be able to learn from your code. All hosted plugins can be found and installed from within QGIS with the Plugin Manager. Information and requirements are here: `plugins.qgis.org `_.