Example: Recording Changes of Variable Values

Visualization elements whose variable value has changed as a result of user input call the IValueChangedListener interface. With this interface, the value changes can be recorded and then processed programmatically.

Project VisuValueChangeHandler.project:

The FB_ValueChangedListener function block implements the IValueChangedListener interface. The ValueChangedListenerManager function block is registered in the PLC_PRG program.

When the value of a visualization element changes, the ValueChanged method of the FB_ValueChangedListener function block is called.

In the sample project, all user inputs of the visualization are written to the log file of the device. You can use the Input Assistant to select a respective visualization element.