Desenvolvimento de Complementos Python

It is possible to create plugins in Python programming language. In comparison with classical plugins written in C++ these should be easier to write, understand, maintain and distribute due the dynamic nature of the Python language.

Python plugins are listed together with C++ plugins in QGIS plugin manager. They’re being searched for in these paths:

  • UNIX/Mac: ~/.qgis/python/plugins e (qgis_prefix)/share/qgis/python/plugins

  • Windows: ~/.qgis/python/plugins e (qgis_prefix)/python/plugins

Home directory (denoted by above ~) on Windows is usually something like C:\Documents and Settings\(user) (on Windows XP or earlier) or C:\Users\(user). Since Quantum GIS is using Python 2.7, subdirectories of these paths have to contain an __init__.py fily to be considered Python packages that can be imported as plugins.

Passos:

  1. 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?
  2. Create files: Create the files described next. A starting point (__init.py__). Fill in the Plugin metadata (metadata.txt) A main python plugin body (mainplugin.py). A form in QT-Designer (form.ui), with its resources.qrc.
  3. Write code: Write the code inside the mainplugin.py
  4. Test: Close and re-open QGIS and import your plugin again. Check if everything is OK.
  5. Publish: Publish your plugin in QGIS repository or make your own repository as an “arsenal” of personal “GIS weapons”

Escrevendo um complemento

Since the introduction of python plugins in QGIS, a number of plugins have appeared - on Plugin Repositories wiki page you can find some of them, you can use their source to learn more about programming with PyQGIS or find out whether you are not duplicating development effort. QGIS team also maintains an Repositório oficial de complementos python. Ready to create a plugin but no idea what to do? Python Plugin Ideas wiki page lists wishes from the community!

arquivos de complementos

Here’s the directory structure of our example plugin:

PYTHON_PLUGINS_PATH/
  MyPlugin/
    __init__.py    --> *required*
    mainPlugin.py  --> *required*
    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:

  • __init__.py = The starting point of the plugin. It has to have the classFactory method and may have any other initialisation code.
  • mainPlugin.py = The main working code of the plugin. Contains all the information about the actions of the plugin and the main code.
  • resources.qrc = The .xml document created by QT-Designer. Contains relative paths to resources of the forms.
  • resources.py = The translation of the .qrc file described above to Python.
  • form.ui = The GUI created by QT-Designer.
  • form.py = The translation of the form.ui described above to Python.
  • metadata.txt = Required for QGIS >= 1.8.0. Containts general info, version, name and some other metadata used by plugins website and plugin infrastructure. Since QGIS 2.0 the metadata from __init__.py are not accepted anymore and the metadata.txt is required.

Here is an online automated way of creating the basic files (skeleton) of a typical QGIS Python plugin.

Also there is a QGIS plugin called Plugin Builder that creates plugin template from QGIS and doesn’t require internet connection. This is the recommended option, as it produces 2.0 compatible sources.

Aviso

If you plan to upload the plugin to the Repositório oficial de complementos python you must check that your plugin follows some additional rules, required for plugin Validação

Conteúdo do complemento

Here you can find information and examples about what to add in each of the files in the file structure described above.

Plugin metadata

First, plugin manager needs to retrieve some basic information about the plugin such as its name, description etc. File metadata.txt is the right place to put this information.

Importante

All metadata must be in UTF-8 encoding.

Metadata name

requerida

Notas

Nome

Verdadeiro

a short string containing the name of the plugin
qgisMinimumVersion

Verdadeiro

dotted notation of minimum QGIS version
qgisMaximumVersion

Falso

dotted notation of maximum QGIS version

Descrição

Verdadeiro

short text which describes the plugin, no HTML allowed

sobre

Falso

longer text which describes the plugin in details, no HTML allowed

Versão

Verdadeiro

short string with the version dotted notation

Autor

Verdadeiro

nome do autor

email

Verdadeiro

e-mail do autor, não será mostrado no site

changelog

Falso

string, can be multiline, no HTML allowed
experimental

Falso

boolean flag, True or False
deprecated

Falso

boolean flag, True or False, applies to the whole plugin and not just to the uploaded version
tags

Falso

comma separated list, spaces are allowe inside individual tags

página inicial

Falso

a valid URL pointing to the homepage of your plugin

Repositório

Falso

a valid URL for the source code repository

rastreador

Falso

a valid URL for tickets and bug reports

Ícone

Falso

a file name or a relative path (relative to the base folder of the plugin’s compressed package)

Categoria

Falso

one of Raster, Vector, Database and Web

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 Raster, Vector, Database and 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 metadata.txt:

category=Raster

Nota

If qgisMaximumVersion is empty, it will be automatically set to the major version plus .99 when uploaded to the Repositório oficial de complementos python.

An example for this metadata.txt:

; the next section is mandatory

[general]
name=HelloWorld
[email protected]
author=Just Me
qgisMinimumVersion=2.0
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
; 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
; synoninms before creating a new one.
tags=wkt,raster,hello world

; these metadata can be empty, they will eventually become mandatory.
homepage=http://www.itopen.it
tracker=http://bugs.itopen.it
repository=http://www.itopen.it/repo
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=2.0

__init__.py

This file is required by Python’s import system. Also, Quantum GIS requires that this file contains a classFactory() function, which is called when the plugin gets loaded to QGIS. It receives reference to instance of QgisInterface and must return instance of your plugin’s class from the mainplugin.py - in our case it’s called TestPlugin (see below). This is how __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. mainPlugin.py):

from PyQt4.QtCore import *
from PyQt4.QtGui import *
from qgis.core import *

# initialize Qt resources from file resouces.py
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")
    QObject.connect(self.action, SIGNAL("triggered()"), 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
    QObject.connect(self.iface.mapCanvas(), SIGNAL("renderComplete(QPainter *)"), \
      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
    QObject.disconnect(self.iface.mapCanvas(), SIGNAL("renderComplete(QPainter *)"), \
      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. mainPlugin.py) are:: - __init__ –> which gives access to Quantum GIS’ interface - initGui() –> called when the plugin is loaded - unload() –> called when the plugin is unloaded

You can see that in the above example, the ``:func:`addPluginToMenu`<http://qgis.org/api/classQgisInterface.html#ad1af604ed4736be2bf537df58d1399c3>`_ is used. This will add the corresponding menu action to the Plugins menu. Alternative methods exist to add the action to a different menu. Here is a list of those methods:

  • addPluginToRasterMenu()
  • addPluginToVectorMenu()
  • addPluginToDatabaseMenu()
  • addPluginToWebMenu()

All of them have the same syntax as the 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")
    QObject.connect(self.action, SIGNAL("triggered()"), 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 QAction and QMenu objectName to a name specific to your plugin so that it can be customized.

Arquivo de Recursos

You can see that in initGui() we’ve used an icon from the resource file (called resources.qrc in our case):

<RCC>
  <qresource prefix="/plugins/testplug" >
     <file>icon.png</file>
  </qresource>
</RCC>

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 pyrcc4 command:

pyrcc4 -o resources.py resources.qrc

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 to your QGIS installation.

Documentação

The documentation for the plugin can be written as HTML help files. The qgis.utils module provides a function, showPluginHelp() which will open the help file browser, in the same way as other QGIS help.

The showPluginHelp`() function looks for help files in the same directory as the calling module. It will look for, in turn, index-ll_cc.html, index-ll.html, index-en.html, index-en_us.html and 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 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.