[QGIS-Developer] Processing algorithm to open up external dialog window

[C Hamilton]

I have been trying to run a processing algorithm that generates a table
from the stats calculated from an input point layer. After the processing
algorithm is run I display an external dialog window and populate that
window with the output results of the processing algorithm. I like using
the processing toolbox because the algorithms run in their own thread and
allow the user to continue working. I don't know if what I am trying to do
is completely possible or not but I am most of the way there, but I have
encountered one problem that I am not sure how to solve. Here is what I
have so far

I run my processing algorithm and then in postProcessingAlgorithm I open up
the dialog window as follows. Note for right now I am calling the plugin
"testcapabilities'. The returned result from processAlgorithm is a table.


from qgis.utils import plugins
...
    def processAlgorithm(self, parameters, context, feedback):
...
        return {self.PrmOutputResults: self.dest_id}
...
    def postProcessAlgorithm(self, context, feedback):
        retval = super().postProcessAlgorithm(context, feedback)
        # This gives me access to the root of my plugin which contains both
the
        # processing algorithm and the post analysis window.
        plugin = plugins['testcapabilities']
        plugin.showDialog()  # This opens up my dialog window
        # This is the input point vector layer in the processing algorithm
        input_layer = self.parameterAsLayer(self.parameters,
self.PrmInputLayer, context)
        # I believe this gives me access to the table layer I generated  in
the algorithm
        table_layer = QgsProcessingUtils.mapLayerFromString(self.dest_id,
context)
        # This is to attach the input and table layers to my dialogs
QgsMaplayerComboBox widgets
        plugin.setData(input_layer,  table_layer)
        return retval

This successfully displays the dialog and passes on the  input_layer  to
the dialog box and will display it in a QgsMaplayerComboBox in the dialog.
The table generated in processAlgorithm is valid in postProcessAlgorithm,
but if I try to have it displayed in a QgsMaplayerComboBox, it does not
work. I think the reason is because it has not yet been added to the QGS
map layers.

Is there a QgsProcessingAlgorithm method that is called after the output
layer has been added to the QGIS layers panel? If there is then at that
point I should be able to add it to my dialog box.

If this is not possible, then I won't be able to use the processing toolbox
and will need to deal with implementing it in my own dialog box and in a
separate thread.

Thanks,

Calvin
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