13. Comunicarea cu utilizatorul

Sugestie

The code snippets on this page need the following imports if you’re outside the pyqgis console:

from qgis.core import (
    QgsMessageLog,
    QgsGeometry,
)

from qgis.gui import (
    QgsMessageBar,
)

from qgis.PyQt.QtWidgets import (
    QSizePolicy,
    QPushButton,
    QDialog,
    QGridLayout,
    QDialogButtonBox,
)

Această secțiune prezintă câteva metode și elemente care ar trebui să fie utilizate pentru a comunica cu utilizatorul, în scopul menținerii coerenței interfaței cu utilizatorul.

13.1. Showing messages. The QgsMessageBar class

Folosirea casetelor de mesaje poate fi o idee rea, din punctul de vedere al experienței utilizatorului. Pentru a arăta o mică linie de informații sau un mesaj de avertizare/eroare, bara QGIS de mesaje este, de obicei, o opțiune mai bună.

Folosind referința către obiectul interfeței QGIS, puteți afișa un text în bara de mesaje, cu ajutorul următorului cod

from qgis.core import Qgis
iface.messageBar().pushMessage("Error", "I'm sorry Dave, I'm afraid I can't do that", level=Qgis.Critical)

Messages(2): Error : I'm sorry Dave, I'm afraid I can't do that

Fig. 13.33 Bara de mesaje a QGIS

Puteți seta o durată, pentru afișarea pentru o perioadă limitată de timp

iface.messageBar().pushMessage("Ooops", "The plugin is not working as it should", level=Qgis.Critical, duration=3)

Messages(2): Ooops : The plugin is not working as it should

Fig. 13.34 Bara de mesaje a QGIS, cu cronometru

Exemplele de mai sus prezintă o bară de eroare, dar parametrul level poate fi utilizat pentru a crea mesaje de avertizare sau informative, folosind enumerarea Qgis.MessageLevel. Se pot utiliza până la 4 niveluri diferite:

0. Info

1. Warning

2. Critical

3. Success

Fig. 13.35 Bara de mesaje a QGIS (info)

Widget-urile pot fi adăugate la bara de mesaje, cum ar fi, de exemplu, un buton pentru afișarea mai multor informații

def showError():
    pass

widget = iface.messageBar().createMessage("Missing Layers", "Show Me")
button = QPushButton(widget)
button.setText("Show Me")
button.pressed.connect(showError)
widget.layout().addWidget(button)
iface.messageBar().pushWidget(widget, Qgis.Warning)

Messages(1): Missing Layers : Show Me

Fig. 13.36 Bara de mesaje a QGIS, cu un buton

Puteți utiliza o bară de mesaje chiar și în propria fereastră de dialog, în loc să apelați la o casetă de text, sau să arătați mesajul în fereastra principală a QGIS

class MyDialog(QDialog):
    def __init__(self):
        QDialog.__init__(self)
        self.bar = QgsMessageBar()
        self.bar.setSizePolicy( QSizePolicy.Minimum, QSizePolicy.Fixed )
        self.setLayout(QGridLayout())
        self.layout().setContentsMargins(0, 0, 0, 0)
        self.buttonbox = QDialogButtonBox(QDialogButtonBox.Ok)
        self.buttonbox.accepted.connect(self.run)
        self.layout().addWidget(self.buttonbox, 0, 0, 2, 1)
        self.layout().addWidget(self.bar, 0, 0, 1, 1)
    def run(self):
        self.bar.pushMessage("Hello", "World", level=Qgis.Info)

myDlg = MyDialog()
myDlg.show()

Fig. 13.37 Bara de mesaje a QGIS, într-o fereastră de dialog

13.2. Afișarea progresului

Barele de progres pot fi, de asemenea, incluse în bara de mesaje QGIS, din moment ce, așa cum am văzut, aceasta acceptă widget-uri. Iată un exemplu pe care îl puteți încerca în consolă.

import time
from qgis.PyQt.QtWidgets import QProgressBar
from qgis.PyQt.QtCore import *
progressMessageBar = iface.messageBar().createMessage("Doing something boring...")
progress = QProgressBar()
progress.setMaximum(10)
progress.setAlignment(Qt.AlignLeft|Qt.AlignVCenter)
progressMessageBar.layout().addWidget(progress)
iface.messageBar().pushWidget(progressMessageBar, Qgis.Info)

for i in range(10):
    time.sleep(1)
    progress.setValue(i + 1)

iface.messageBar().clearWidgets()

Messages(0): Doing something boring...

Also, you can use the built-in status bar to report progress, as in the next example:

vlayer = iface.activeLayer()

count = vlayer.featureCount()
features = vlayer.getFeatures()

for i, feature in enumerate(features):
    # do something time-consuming here
    print('.') # printing should give enough time to present the progress

    percent = i / float(count) * 100
    # iface.mainWindow().statusBar().showMessage("Processed {} %".format(int(percent)))
    iface.statusBarIface().showMessage("Processed {} %".format(int(percent)))

iface.statusBarIface().clearMessage()

13.3. Jurnalizare

There are three different types of logging available in QGIS to log and save all the information about the execution of your code. Each has its specific output location. Please consider to use the correct way of logging for your purpose:

• QgsMessageLog is for messages to communicate issues to the user. The output of the QgsMessageLog is shown in the Log Messages Panel.

• The python built in logging module is for debugging on the level of the QGIS Python API (PyQGIS). It is recommended for Python script developers that need to debug their python code, e.g. feature ids or geometries

• QgsLogger is for messages for QGIS internal debugging / developers (i.e. you suspect something is triggered by some broken code). Messages are only visible with developer versions of QGIS.

Examples for the different logging types are shown in the following sections below.

Atenționare

Use of the Python print statement is unsafe to do in any code which may be multithreaded and extremely slows down the algorithm. This includes expression functions, renderers, symbol layers and Processing algorithms (amongst others). In these cases you should always use the python logging module or thread safe classes (QgsLogger or QgsMessageLog) instead.

13.3.1. QgsMessageLog

# You can optionally pass a 'tag' and a 'level' parameters
QgsMessageLog.logMessage("Your plugin code has been executed correctly", 'MyPlugin', level=Qgis.Info)
QgsMessageLog.logMessage("Your plugin code might have some problems", level=Qgis.Warning)
QgsMessageLog.logMessage("Your plugin code has crashed!", level=Qgis.Critical)

MyPlugin(0): Your plugin code has been executed correctly
(1): Your plugin code might have some problems
(2): Your plugin code has crashed!

Notă

You can see the output of the QgsMessageLog in the Log Messages Panel

13.3.2. The python built in logging module

import logging
formatter = '%(asctime)s - %(name)s - %(levelname)s - %(message)s'
logfilename=r'c:\temp\example.log'
logging.basicConfig(filename=logfilename, level=logging.DEBUG, format=formatter)
logging.info("This logging info text goes into the file")
logging.debug("This logging debug text goes into the file as well")

The basicConfig method configures the basic setup of the logging. In the above code the filename, logging level and the format are defined. The filename refers to where to write the logfile to, the logging level defines what levels to output and the format defines the format in which each message is output.

2020-10-08 13:14:42,998 - root - INFO - This logging text goes into the file
2020-10-08 13:14:42,998 - root - DEBUG - This logging debug text goes into the file as well

If you want to erase the log file every time you execute your script you can do something like:

if os.path.isfile(logfilename):
    with open(logfilename, 'w') as file:
        pass

Further resources on how to use the python logging facility are available at:

• https://docs.python.org/3/library/logging.html

• https://docs.python.org/3/howto/logging.html

• https://docs.python.org/3/howto/logging-cookbook.html

Atenționare

Please note that without logging to a file by setting a filename the logging may be multithreaded which heavily slows down the output.