Control accessors perform side effects on other attributes when they are evaluated. They represent the control structures and instructions of a programming language. In the Group Inspector, you can view them from the “Behaviors” and “Interaction” notebook pages, under the “do” clause attached to each attribute.

The different Control accessors are described as follows:

The Assign accessor (class IlvTriggerAccessor) is used to assign a value to another attribute or sub-attribute. When the attribute is set, the target attribute specified by the target parameter is assigned the specified value.

The lcd2 prototype of the lcd library uses the Assign accessor.

The Condition accessor (class IlvConditionAccessor) is used to perform a conditional assignment of another attribute when the attribute is changed.

The first parameter defines a condition operator that is applied to the new value of the attribute. For example, if the value of the attribute is changed to 10, the operator parameter is >, and the operand is 5, the condition tested is 10 > 5. If the operator is [Operand_value], the condition tested is only the value of the operand parameter (that is, the new value passed to changeValue is ignored).

Depending on the test result, the attribute specified by the Attribute parameter is set to one of two values: Value if True or Value if False. The parameters Operand, Value if True, or Value if False can be either immediate values (such as 1 or "red"), the names of other attributes that will be queried to get the values used, or an expression containing these immediate values or attribute names.

The following example shows the thermo prototype in the samples prototype library. If the temperature attribute is above 30, the gauge is drawn in red. Otherwise, it is drawn in blue.

The Format accessor (class IlvFormatAccessor) can be used to convert a numeric value of type Double to a character string using a user-specified format. The formatted string is then copied to another accessor. The format of the value is specified by the Format parameter, which is defined in the C library function printf. The numeric value is passed to the conversion function as an IlDouble, so the format should contain a %g specifier.

In the display prototype in the samples prototype library, the Format accessor allows you to change in NumberField.label the way the value is displayed.

The Increment accessor (class IlvCounterAccessor) is used to increment another attribute. Each time the attribute containing this attribute is set, another attribute, called a counter, is increased by one until a specified maximum value is reached. When this value is reached, the counter is reset to zero.

A three-state button can be implemented by using a Counter accessor linked to a MultiRep accessor. The following accessor has been added to the symbol prototype of the samples prototype library. Changing the state_incr value in the Attributes notebook page of the Group Inspector increments the state and switches its representation.

The Min/Max accessor (class IlvMinMaxAccessor) is similar to the Condition accessor but handles common cases when an attribute must be tested against a minimum and a maximum threshold. When the attribute is changed, another attribute is set. The assigned value depends on whether the value of the current attribute is less than the minimum, between the minimum and the maximum, or greater than the maximum. In addition, an exception condition can be specified: if the exception condition is true, no value is changed.

This accessor is attached to a Temperature attribute. When Temperature is set, if Nobody’s at Home is true, nothing is done. If the Temperature is below 15, HeatOn is assigned to ClimateControl. If Temperature is above 25, CoolingOn is assigned to ClimateControl. If the temperature is between 15 and 25, AllOff is assigned to ClimateControl.

This example shows the vertGauge prototype in the sample library.

The Multiple accessor (class IlvCompositeAccessor) assigns the value of the attribute to multiple other attributes or sub-attributes. It can be used, for example, to change the colors of two graphic nodes using a single public value of the prototype.

This example shows the Color accessor in the thermo prototype.

The Notify accessor (class IlvOutputAccessor) turns changeValue calls on the attribute to which it is attached into pushValue calls. Values that are watching the given attribute will execute all their behaviors.

This accessor triggers behaviors of other attributes that depend on the notifying value. For example, you can make a change in the Threshold attribute to also re-evaluate the Temperature attribute. This can be done by attaching a Notify accessor to the Threshold attribute, and a Watch (Threshold) behavior to the Temperature attribute.

The following example shows the X_Scale attributes of the transformer prototype in the samples library.

This accessor is described in Data accessors under Script.

The Switch accessor (class IlvSwitchAccessor) implements a switch statement.

A traffic light with varying settings can be implemented like this:

The Toggle accessor (class IlvToggleAccessor) switches another attribute between true and false each time the attribute is set. The value assigned to the attribute containing a toggle behavior is ignored.

The following example shows the random prototype in the sources prototype library with the value toggle.