Over time, we have introduced more and more features aimed at making apps more dynamic. By dynamic, we mean the ability for apps to change their appearance and behavior based on data entered by your users. We added calculated properties early last year, making it possible to use formulas to determine things like the recipients of reports and whether a field or a button should be visible or grayed out .
We’re now taking the next logical step and enabling formulas to be
used to determine labels, validation messages and field units. Let’s
say that you have a drop-down field that enables users to choose
between metric and imperial units. You can associate a formula with
the TrailingUnit property of all weight fields that selects
the unit “kg” if metric units have been selected and “lbs” otherwise:
IF(UnitSelector =
"Metric", " kg", " lbs").
Validation messages appear when fields fail validation. Let’s say
that you associate the following formula with the Valid
property of a field named Tonnage: (Tonnage = DefaultTonnage) ||
(Tonnage < MaximumTonnage), where there is a field named
MaximumTonnage determining the maximum value for the
Tonnage field and another field named
DefaultTonnage specifying a default value. Tonnage
is valid if it is below that maximum value or equal to the default
value. What should the validation message say if the field fails
validation? With a formula-driven validation message, you can
associate the following formula with the ValidationMessage
property of the Tonnage field: "If not " &
DefaultTonnage.FormattedValue & ", must be less than " &
MaximumTonnage.FormattedValue & "."
Use the Label property of groups, fields, buttons, panels
and list panel options to change their labels through formulas. Let’s
say that you use a stepper to enable your users to
add and remove fields, a technique we demonstrated in
January, and that the field with the stepper is named
NumberOfVisibleFields. Further, assume that there is a
button below the fields that sends a report with their
values. To make the button label indicate the number of records that
are sent, associate the following formula with its Label
property: "Send "
& NumberOfVisibleFields & " records."
Many calculated properties are exposed through the inspector, where you can press the faint fx button to edit their formulas. In an effort not to clutter the inspector with advanced and rarely-used properties, it does not contain all calculated properties. Before this release, the most notable example was the InitialValue property, allowing you to set initial field values through formulas. You won’t find the Label, ValidationMessage, LeadingUnit and TrailingUnit properties in the inspector, either. Rather, you must use the property selector to edit their formulas:
We have written a new sample app that uses the Label property to enable the user to name fields. Check it out!