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Code Snippets

This section features code snippets to facilitate plugin development.

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")

How to toggle Layers

There is an API to access layers in the legend. Here is an example that toggles the visibility of the active layer

root = QgsProject.instance().layerTreeRoot()
node = root.findLayer(iface.activeLayer().id())
new_state = Qt.Checked if node.isVisible() == Qt.Unchecked else Qt.Unchecked
node.setItemVisibilityChecked(new_state)

How to access attribute table of selected features

def change_value(value):
    """Change the value in the second column for all selected features.

    :param value: The new value.
    """
    layer = iface.activeLayer()
    if layer:
        count_selected = layer.selectedFeatureCount()
        if count_selected > 0:
            layer.startEditing()
            id_features = layer.selectedFeatureIds()
            for i in id_features:
                layer.changeAttributeValue(i, 1, value) # 1 being the second column
            layer.commitChanges()
        else:
            iface.messageBar().pushCritical("Error",
                "Please select at least one feature from current layer")
    else:
        iface.messageBar().pushCritical("Error", "Please select a layer")

The method requires one parameter (the new value for the second field of the selected feature(s)) and can be called by

changeValue(50)