Custom Transformers and Parameter Input

FME transformers all have parameters whose value can be supplied by attributes or by user input. The same is still true of transformers inside a custom transformer definition. However, because a custom transformer can be reused in multiple places, it's important for these inputs to be flexible.

Parameter Input by Attributes

Many transformer parameters can be set up to accept values from attributes.

Take this custom transformer that creates custom map labels:

Inside that custom transformer is a LabelPointReplacer transformer. It uses AddressID as the value for the label:

As created, the custom transformer works fine. However, consider if that transformer is used elsewhere, where AddressID does not exist:

This transformer is flagged as "incomplete". It is used in a scenario where AddressID is not available.

Parameter Input by User Parameters

Besides attributes, most FME parameters can be set up to accept values from User Parameters.

In a similar setup to above, here a custom transformer contains a LabelPointReplacer transformer whose label value is selected by user input:

Here the issue is not where the custom transformer is used, but its duplication. If each instance of the custom transformer uses the same user parameter, then they will all get the same input.

We need a mechanism for the user to enter different values per transformer instance.