Tutorial 2. How to modify visual elements using embedded script language PDF Print E-mail
Written by Michael   
Tuesday, 18 August 2009
FreeSCADA has embedded language based on Python syntax which allows you to customize your scheme in various ways. In this example I will show how to handle events from visual elements and modify visual state of these objects. FreeSCADA has embedded language based on Python syntax which allows you to customize your scheme in various ways. In this example I will show how to handle events from visual elements and modify visual state of these objects.

First, we need to create new schema and put Rectangle element on it.
Designer window with single rectangle

Using scripting, I’d like to change color of this rectangle to blue when mouse cursor in this rectangle and to red when it outside of this area. So, we will need 3 events:
  • MouseEnter – occurs when mouse pointer enters to this element.
  • MouseLeave – occurs when mouse pointer is moved outside of the element.
  • Loaded – This event occurs at very beginning when schema just loaded into memory. In our case it can be used to handle initialization stage.
Now let’s create handlers for these events. Go to Property Browser window and click “Event” button.
Property browser


You will see full list of event. Find “MouseEnter” row and type your handler name in editable field. At the end hit Enter to create this handler.
Creating event handler

By pressing Enter Designer will create a placeholder for this event and open Script editor window. But let’s switch back to schema and create the rest two handlers: MouseLeave and Loaded.
Finally you get see the following script text with 3 placeholders for our handlers.
Script window with 3 placeholders

The last step is to create some logic for them. I will set color property for the rectangle using “Colors” class from WPF class library. Therefore I need to add reference to WPF in the script (please refer to IronPython documentation for details).

import clr
clr.AddReferenceByPartialName("PresentationCore")
from System.Windows.Media import *

This code snippet says that we import core python library “clr” and add reference to “PresentationCore” .Net library. Since I don’t want to write full name for “Colors” class (like System.Windows.Media.Colors) I imported its namespace into script namespace.

Now we can enrich visual element handler by some code:
# Arguments: Object sender, MouseEventArgs e
def OnMouseEnter(sender, e):
    sender.Fill.Color = Colors.LightSkyBlue

# Arguments: Object sender, MouseEventArgs e
def OnMouseLeave(sender, e):
    sender.Fill.Color = Colors.Red

# Arguments: Object sender, RoutedEventArgs e
def OnLoaded(sender, e):
    sender.Fill.Color = Colors.Red

Looks pretty simple, isn’t it? Now click “check syntax” button just to make sure that everything is correct with our code.
Check syntax button


Finally the script should look like on the picture below.
Final picture

Now you can save this project and open it in Runtime module.
Last Updated ( Monday, 24 August 2009 )
 
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