Calling the correct element of an output via PyQGIS Script

Question

I am trying to apply a style to the output file of a script that I´m running from the toolbox in QGIS 3.4.7. The last step is as described below.

        def processAlgorithm(self, parameters, context, feedback):

        if parameters['Input1'] is not None:
            source = self.parameterAsSource(parameters,'Input1',context)
            (sink, dest_id3) = self.parameterAsSink(parameters,'Output1',context,source.fields(),source.wkbType(),source.sourceCrs())
            total = 100.0 / source.featureCount() if source.featureCount() else 0
            features = source.getFeatures()
            for current, feature in enumerate(features):
                sink.addFeature(feature, QgsFeatureSink.FastInsert)
                feedback.setProgress(int(current * total))

After that, I would like to apply a fixed style to the output file so that it will be displayed on Layers with the applied style. I reached the lines below:

                self.source.loadNamedStyle(u"C:\\Users\\ct279359\\Desktop\\Styles\\Roads.qml")
                self.source.triggerRepaint() 

I got this error:

AttributeError: 'InOut' object has no attribute 'source'

I would like to know the correct way to call the output file created in the first part.

I did some research on the subject Here, Here, Here, Here, Here and Here.

All explain ways to invoke the QML file or how to change the style of a file that is already in the Layers section. I need next to this, to invoke the correct output file.

-------------------------------------------------------------
Full code here.

from qgis.PyQt.QtCore import QCoreApplication
from qgis.core import (QgsProcessing,
                       QgsFeatureSink,
                       QgsProcessingException,
                       QgsProcessingAlgorithm,
                       QgsProcessingParameterVectorLayer,
                       QgsProcessingParameterFeatureSink,
                       QgsProcessingParameterRasterLayer,
                       QgsProcessingParameterRasterDestination,
                       QgsVectorLayer,
                       QgsProject)
import processing

class InOut(QgsProcessingAlgorithm):

    def tr(self, string):
        return QCoreApplication.translate('Processing', string)

    def createInstance(self):
        return InOut()

    def name(self):
        return 'InOut2'

    def displayName(self):
        return self.tr('InOut2')

    def group(self):
        return self.tr('Auxiliares')

    def groupId(self):
        return 'auxiliares1'


    def initAlgorithm(self, config=None):
        self.addParameter(QgsProcessingParameterVectorLayer('Input1','Input1',optional=True, types=[QgsProcessing.TypeVector], defaultValue=None))
        self.addParameter(QgsProcessingParameterFeatureSink('Output1','Output1', type=QgsProcessing.TypeVectorAnyGeometry, createByDefault=True, defaultValue=None))

    def processAlgorithm(self, parameters, context, feedback):

        if parameters['Input1'] is not None:
            source = self.parameterAsSource(parameters,'Input1',context)
            (sink, dest_id3) = self.parameterAsSink(parameters,'Output1',context,source.fields(),source.wkbType(),source.sourceCrs())
            total = 100.0 / source.featureCount() if source.featureCount() else 0
            features = source.getFeatures()
            for current, feature in enumerate(features):
                sink.addFeature(feature, QgsFeatureSink.FastInsert)
                feedback.setProgress(int(current * total))

                self.source.loadNamedStyle(u"C:\\Users\\ct279359\\Desktop\\Styles\\Roads.qml")
                self.source.triggerRepaint()

        return results

Answer 1

You need to turn the layer into a QGIS vector layer when importing it:

        #define vector layer  
        vlayer = QgsVectorLayer('your_output_file', 'layer_name', "ogr")
        # add the layer to the registry
        QgsProject.instance().addMapLayer(vlayer)
        # load style
        vlayer.loadNamedStyle('path_to_qml.qml')