.. only:: html .. index:: Plugins; User interaction *************************** Communicating with the user *************************** .. contents:: :local: This section shows some methods and elements that should be used to communicate with the user, in order to keep consistency in the User Interface. Showing messages. The QgsMessageBar class ========================================= Using message boxes can be a bad idea from a user experience point of view. For showing a small info line or a warning/error messages, the QGIS message bar is usually a better option. Using the reference to the QGIS interface object, you can show a message in the message bar with the following code .. code-block:: python from qgis.core import Qgis iface.messageBar().pushMessage("Error", "I'm sorry Dave, I'm afraid I can't do that", level=Qgis.Critical) .. figure:: img/errorbar.png :align: center :width: 40em QGIS Message bar You can set a duration to show it for a limited time .. code-block:: python iface.messageBar().pushMessage("Ooops", "The plugin is not working as it should", level=Qgis.Critical, duration=3) .. figure:: img/errorbar-timed.png :align: center :width: 40em QGIS Message bar with timer The examples above show an error bar, but the ``level`` parameter can be used to creating warning messages or info messages, using the :class:`Qgis.MessageLevel ` enumeration. You can use up to 4 different levels: 0. Info 1. Warning 2. Critical 3. Success .. figure:: img/infobar.png :align: center :width: 40em QGIS Message bar (info) Widgets can be added to the message bar, like for instance a button to show more info .. code-block:: python 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) .. figure:: img/bar-button.png :align: center :width: 40em QGIS Message bar with a button You can even use a message bar in your own dialog so you don't have to show a message box, or if it doesn't make sense to show it in the main QGIS window .. code-block:: python 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() .. figure:: img/dialog-with-bar.png :align: center :width: 40em QGIS Message bar in custom dialog Showing progress ================ Progress bars can also be put in the QGIS message bar, since, as we have seen, it accepts widgets. Here is an example that you can try in the console. .. code-block:: python 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() Also, you can use the built-in status bar to report progress, as in the next example: .. code-block:: python vlayer = QgsProject.instance().mapLayersByName("countries")[0] 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() Logging ======= You can use the QGIS logging system to log all the information that you want to save about the execution of your code. .. code-block:: python # 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) .. warning:: Use of the Python ``print`` statement is unsafe to do in any code which may be multithreaded. This includes **expression functions**, **renderers**, **symbol layers** and **Processing algorithms** (amongst others). In these cases you should always use thread safe classes (:class:`QgsLogger ` or :class:`QgsMessageLog `) instead. .. note:: You can see the output of the :class:`QgsMessageLog ` in the :ref:`log_message_panel` .. note:: * :class:`QgsLogger ` is for messages for debugging / developers (i.e. you suspect they are triggered by some broken code) * :class:`QgsMessageLog ` is for messages to investigate issues by sysadmins (e.g. to help a sysadmin to fix configurations)