Dezvoltarea plugin-urilor Python¶

Fișierele Plugin-ului¶

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*

Care este semnificația fișierelor:

• __init__.py = The starting point of the plugin. It has to have the classFactory method and may have any other initialisation code.

• mainPlugin.py = Principalul codul lucrativ al plugin-ului. Conține toate informațiile cu privire la acțiunile plugin-ului și ale codului principal.

• resources.qrc = The .xml document created by QT-Designer. Contains relative paths to resources of the forms.

• resources.py = Traducerea fișierului .qrc descris mai sus.

• form.ui = The GUI created by QT-Designer.

• form.py = Traducerea form.ui descris mai sus.

• metadata.txt = Necesar pentru QGIS >= 1.8.0. Conține informații generale, versiunea, numele și alte metadate utilizate de către site-ul de plugin-uri și de către infrastructura plugin-ului. Începând cu QGIS 2.0 metadatele din __init__.py nu mai sunt acceptate, iar metadata.txt este necesar.

Aici este o modalitate on-line, automată, de creare a fișierelor de bază (carcase) pentru un plugin tipic QGIS Python.

De asemenea, există un plugin QGIS numit Plugin Builder care creează un șablon de plugin QGIS și nu are nevoie de conexiune la internet. Aceasta este opțiunea recomandată, atât timp cât produce surse compatibile 2.0.

|Metadatele plugin-ului¶

În primul rând, managerul de plugin-uri are nevoie de preluarea câtorva informații de bază despre plugin, cum ar fi numele, descrierea etc. Fișierul metadata.txt este locul potrivit pentru a reține această informație.

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

An example for this metadata.txt:

; the next section is mandatory

[general]
name=HelloWorld
email=me@example.com
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()

Toate acestea au aceeași sintaxă ca metoda addPluginToMenu().

Adăugarea unui meniu la plugin-ul dvs. printr-una din metoldele predefinite este recomandată pentru a păstra coerența în stilul de organizare a plugin-urilor. Cu toate acestea, puteți adăuga grupul dvs. de meniuri personalizate direct în bara de meniu, așa cum demonstrează următorul exemplu :

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()

Nu uitați să setați QAction și QMenu objectName unui nume specific plugin-ului dvs, astfel încât acesta să poată fi personalizat.

Fișier de resurse¶

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.

Când lucrați la un plug-in real, este înțelept să stocați plugin-ul într-un alt director (de lucru), și să creați un fișier make care va genera UI + fișierele de resurse și să instalați plugin-ul în instalarea QGIS.