Wrong or missing parameter QgsProcessingParameterFile QGIS 3.4 Python plugin

Question

I'm making a script that can be called by the processing.execAlgorithmDialog function. For one of the parameters, I want to use the QgsProcessingParameterFile class for selecting a .csv file.

I tried the following:

class T4_Visualiseer_Networks_Resultaat(QgsProcessingAlgorithm):

    PrmOutputFile = 'Networks result'

    self.addParameter(
        QgsProcessingParameterFile(
            name=self.PrmOutputFile,
            description="Networks resultaat",
            extension="csv(*.csv)"
        )
    )

    def processAlgorithm(self, parameters, context, feedback):
        # Some code to do after clicking ok

When I select a .csv file in a folder and press OK to begin the script, I get the message Wrong or missing parameter value: Networks resultaat (see picture below).

I already tried the following:

• Replace / by \
• Add behavior=0 to make sure a file is selected (this was already the case because the default value for behavior is 0)
• Rename the .csv file

None of the above actions fixed the problem of getting this message and I can't find any other solutions on the internet.

Do you have any idea what the problem can be or how I can fix it?

Answer 1

In the code source you can read The extension argument allows for specifying a file extension associated with the parameter (e.g. "html"). Use fileFilter for a more flexible approach which allows for multiple file extensions. Only one of extension or fileFilter should be specified, if both are specified then fileFilter takes precedence.

Hence, you have to put the extension: "csv", "csv(*.csv)" is valid for the parameter fileFilter.