Creating QgsVectorLayer in QThread using PyQt and GIS

In this tutorial, we will be discussing how to create a QgsVectorLayer in a QThread using PyQt’s threading module. This can be useful when you want to perform time-consuming operations in the background without blocking the main user interface of your application.

First, make sure you have PyQt installed on your system. You can install it using pip:

pip install PyQt5

Next, let’s create a new Python file and import the necessary modules:

import sys
from qgis.core import QgsVectorLayer, QgsFields, QgsField, QgsFeature, QgsGeometry
from PyQt5.QtCore import QThread

Now let’s create a custom QThread subclass that will handle the creation of the QgsVectorLayer:

class VectorLayerThread(QThread):
    def __init__(self, layer_name, crs):
        super().__init__()
        self.layer_name = layer_name
        self.crs = crs

    def run(self):
        fields = QgsFields()
        fields.append(QgsField('name', 10))
        fields.append(QgsField('value', 6))

        # Create the vector layer
        layer = QgsVectorLayer('Point?crs=' + self.crs, self.layer_name, 'memory')
        layer.provider().addAttributes(fields)
        layer.updateFields()

        # Add a point feature to the layer
        feature = QgsFeature(layer.fields())
        feature.setGeometry(QgsGeometry.fromPointXY(QgsPointXY(0, 0)))
        feature.setAttributes(['Point 1', 10])
        layer.dataProvider().addFeatures([feature])

        # Add the layer to the QgsMapLayerRegistry and emit a signal when finished
        QgsProject.instance().addMapLayer(layer)
        self.finished.emit()

In the code above, we first define a custom QThread subclass called VectorLayerThread that takes the layer name and CRS as arguments. In the run method, we create a new QgsVectorLayer with the specified CRS and name. We then add fields, create a feature, set attributes, and add the feature to the layer’s data provider. Finally, we add the layer to the QgsProject and emit a signal to indicate that the thread has finished.

Now let’s create a simple PyQt application that will create and run an instance of the VectorLayerThread:

if __name__ == '__main__':
    from PyQt5.QtWidgets import QApplication

    app = QApplication(sys.argv)

    # Create and start the VectorLayerThread
    thread = VectorLayerThread('test_layer', 'EPSG:4326')
    thread.finished.connect(app.quit)
    thread.start()

    sys.exit(app.exec_())

In the code above, we create a QApplication instance and start the VectorLayerThread with the name ‘testlayer’ and the CRS ‘EPSG:4326’. We then connect the thread’s finished signal to the app.quit method and start the thread using thread.start(). Finally, we run the application using app.exec().

That’s it! You have now successfully created a QgsVectorLayer in a QThread using PyQt’s threading module. This allows you to perform time-consuming operations in the background without blocking the main user interface of your application. Feel free to modify the code to suit your specific needs and requirements.