16.2. Code Snippets

Hint

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

from qgis.core import (
    QgsProject,
    QgsApplication,
    QgsMapLayer,
)

from qgis.gui import (
    QgsGui,
    QgsOptionsWidgetFactory,
    QgsOptionsPageWidget,
    QgsLayerTreeEmbeddedWidgetProvider,
    QgsLayerTreeEmbeddedWidgetRegistry,
)

from qgis.PyQt.QtCore import Qt
from qgis.PyQt.QtWidgets import (
    QMessageBox,
    QAction,
    QHBoxLayout,
    QComboBox,
)
from qgis.PyQt.QtGui import QIcon

This section features code snippets to facilitate plugin development.

16.2.1. How to call a method by a key shortcut

In the plug-in add to the initGui()

self.key_action = QAction("Test Plugin", self.iface.mainWindow())
self.iface.registerMainWindowAction(self.key_action, "Ctrl+I")  # action triggered by Ctrl+I
self.iface.addPluginToMenu("&Test plugins", self.key_action)
self.key_action.triggered.connect(self.key_action_triggered)

To unload() add

self.iface.unregisterMainWindowAction(self.key_action)

The method that is called when CTRL+I is pressed

def key_action_triggered(self):
  QMessageBox.information(self.iface.mainWindow(),"Ok", "You pressed Ctrl+I")

It is also possible to allow users to customize key shortcuts for the provided actions. This is done by adding:

# in the initGui() function
QgsGui.shortcutsManager().registerAction(self.key_action)

# and in the unload() function
QgsGui.shortcutsManager().unregisterAction(self.key_action)

16.2.2. How to reuse QGIS icons

Because they are well-known and convey a clear message to the users, you may want sometimes to reuse QGIS icons in your plugin instead of drawing and setting a new one. Use the getThemeIcon() method.

For example, to reuse the mActionFileOpen.svg icon available in the QGIS code repository:

# e.g. somewhere in the initGui
self.file_open_action = QAction(
    QgsApplication.getThemeIcon("/mActionFileOpen.svg"),
    self.tr("Select a File..."),
    self.iface.mainWindow()
)
self.iface.addPluginToMenu("MyPlugin", self.file_open_action)

iconPath() is another method to call QGIS icons. Find examples of calls to theme icons at QGIS embedded images - Cheatsheet.

16.2.3. Interface for plugin in the options dialog

You can add a custom plugin options tab to Settings ► Options. This is preferable over adding a specific main menu entry for your plugin’s options, as it keeps all of the QGIS application settings and plugin settings in a single place which is easy for users to discover and navigate.

The following snippet will just add a new blank tab for the plugin’s settings, ready for you to populate with all the options and settings specific to your plugin. You can split the following classes into different files. In this example, we are adding two classes into the main mainPlugin.py file.

class MyPluginOptionsFactory(QgsOptionsWidgetFactory):

    def __init__(self):
        super().__init__()

    def icon(self):
        return QIcon('icons/my_plugin_icon.svg')

    def createWidget(self, parent):
        return ConfigOptionsPage(parent)


class ConfigOptionsPage(QgsOptionsPageWidget):

    def __init__(self, parent):
        super().__init__(parent)
        layout = QHBoxLayout()
        layout.setContentsMargins(0, 0, 0, 0)
        self.setLayout(layout)

Finally we are adding the imports and modifying the __init__ function:

from qgis.PyQt.QtWidgets import QHBoxLayout
from qgis.gui import QgsOptionsWidgetFactory, QgsOptionsPageWidget


class MyPlugin:
    """QGIS Plugin Implementation."""

    def __init__(self, iface):
        """Constructor.

        :param iface: An interface instance that will be passed to this class
            which provides the hook by which you can manipulate the QGIS
            application at run time.
        :type iface: QgsInterface
        """
        # Save reference to the QGIS interface
        self.iface = iface


    def initGui(self):
        self.options_factory = MyPluginOptionsFactory()
        self.options_factory.setTitle(self.tr('My Plugin'))
        iface.registerOptionsWidgetFactory(self.options_factory)

    def unload(self):
        iface.unregisterOptionsWidgetFactory(self.options_factory)

Tip

Add custom tabs to layer properties dialog

You can apply a similar logic to add the plugin custom option to the layer properties dialog using the classes QgsMapLayerConfigWidgetFactory and QgsMapLayerConfigWidget.

16.2.4. Embed custom widgets for layers in the layer tree

Beside usual layer symbology elements displayed next or below the layer entry in the Layers panel, you can add your own widgets, allowing for quick access to some actions that are often used with a layer (setup filtering, selection, style, refreshing a layer with a button widget, create a layer based time slider or just show extra layer information in a Label there, or …). These so-called Layer tree embedded widgets are made available through the layer’s properties Legend tab for individual layers.

The following code snippet creates a drop-down in the legend which shows you the layer-styles available for the layer, allowing to quickly switch between the different layer styles.

class LayerStyleComboBox(QComboBox):
    def __init__(self, layer):
        QComboBox.__init__(self)
        self.layer = layer
        for style_name in layer.styleManager().styles():
            self.addItem(style_name)

        idx = self.findText(layer.styleManager().currentStyle())
        if idx != -1:
          self.setCurrentIndex(idx)

        self.currentIndexChanged.connect(self.on_current_changed)

    def on_current_changed(self, index):
        self.layer.styleManager().setCurrentStyle(self.itemText(index))

class LayerStyleWidgetProvider(QgsLayerTreeEmbeddedWidgetProvider):
    def __init__(self):
        QgsLayerTreeEmbeddedWidgetProvider.__init__(self)

    def id(self):
        return "style"

    def name(self):
        return "Layer style chooser"

    def createWidget(self, layer, widgetIndex):
        return LayerStyleComboBox(layer)

    def supportsLayer(self, layer):
        return True   # any layer is fine

provider = LayerStyleWidgetProvider()
QgsGui.layerTreeEmbeddedWidgetRegistry().addProvider(provider)

Then from a given layer’s Legend properties tab, drag the Layer style chooser from the Available widgets to Used widgets to enable the widget in the layer tree. Embedded widgets are ALWAYS displayed at the top of their associated layer node subitems.

If you want to use the widgets from within e.g. a plugin, you can add them like this:

layer = iface.activeLayer()
counter = int(layer.customProperty("embeddedWidgets/count", 0))
layer.setCustomProperty("embeddedWidgets/count", counter+1)
layer.setCustomProperty("embeddedWidgets/{}/id".format(counter), "style")
view = self.iface.layerTreeView()
view.layerTreeModel().refreshLayerLegend(view.currentLegendNode())
view.currentNode().setExpanded(True)