[QGIS-Developer] How to use addLayerToLoadOnCompletion() ?

[Bourdon, Jean-François (DIF)]

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Hi Devs,

I'm trying to load a raster/vector layer to the current project at the end of the run of a processing algorithm script. I know about QgsProcessingParameterFeatureSink() and I use it when creating a new layer during processing, but how to add an existing layer that will be shown on the map? I tried using context.project().addMapLayer(rlayer, True) but it obviously doesn't work because the process is running in a separate thread. Speaking of thread, I would prefer avoiding running the script in the main thread with
def flags(self):
    return super().flags() | QgsProcessingAlgorithm.FlagNoThreading

I saw this answer from Nyall on SO<https://gis.stackexchange.com/questions/280520/let-qgis-3-0-processing-algorithm-output-a-vectorlayer-loaded-via-the-delimited> for something similar but I haven't been able to emulate. Below is a short example of what I last tried and which gives me the following error: The following layers were not correctly generated. * image_73e75830_4808_4993_abc7_24a5ee61217e You can check the 'Log Messages Panel' in QGIS main window to find more information about the execution of the algorithm.

class addLayerToCanvas(QgsProcessingAlgorithm):
    OUTPUT_raster = 'OUTPUT_raster'

    def initAlgorithm(self, config):
        self.addOutput(QgsProcessingOutputMultipleLayers(self.OUTPUT_raster,
                                                         self.tr('Output raster')))

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

        rlayer = QgsRasterLayer("F:/image.tif", "image") # The layer I want to add to the current project/canvas
        context.addLayerToLoadOnCompletion(rlayer.id(), QgsProcessingContext.LayerDetails('image_layer', QgsProject.instance(), ''))

        return {self.OUTPUT_raster: rlayer.id()}

Thanks for any help

Jean-François Bourdon, ing.f.
Analyste en télédétection
Direction des inventaires forestiers
Ministère des Forêts, de la Faune et des Parcs
5700, 4e Avenue Ouest, local A-108
Québec (Québec) G1H 6R1
Téléphone : 418 627-8669, poste 704304
jean-francois.bourdon at mffp.gouv.qc.ca
mffp.gouv.qc.ca<http://www.mffp.gouv.qc.ca/accueil.jsp>

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