What works (for me) was making a row rule based on the UD field (I don’t have one in Part so I used UserChar01)
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Bind the button to an unused field (not the UD field) I bound mine to
Part.UserInteger1
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Add a Row Rule Like:
Note that to make the rule I initially set the Rule Value:
to x
. This created the function:
private void CreateRowRulePartUserChar1Equals_x()
with the line
RowRule rrCreateRowRulePartUserChar1Equals_x = new RowRule("Part.UserChar1", RuleCondition.Equals, "x", ruleActions);
Which I changed to
RowRule rrCreateRowRulePartUserChar1Equals_x = new RowRule("Part.UserChar1", RuleCondition.Equals, "", ruleActions);
Now whenever UserChar1 is blank, the Test Button becomes disabled.
edit
Whoops … I think you wanted the button disabled when the value was NOT blank. So make your Row Rule accordingly.