Some OLE servers support property change notifications. This means that when a property is about to be changed and again after it has been changed, the server notifies the client, passing information about the change. These messages trigger the events PropertyRequestEdit and PropertyChanged.
When a property is about to change, PowerBuilder triggers the PropertyRequestEdit event. In that event’s script you can:
Find out the name of the property being changed by looking at the PropertyName argument.
Obtain the old property value and save it
The property still has its old value, so you can use the standard syntax to access the value.
Cancel the change by changing the value of the CancelChange argument to TRUE
When a property has changed, PowerBuilder triggers the PropertyChanged event. In that event’s script, you can:
Find out the name of the property being changed by looking at the PropertyName argument
Obtain the new property value
The value has already changed, so you cannot cancel the change.
Because the PropertyName argument is a string, you cannot use it in dot notation to get the value of the property:
value = This.Object.PropertyName // Will not work
Instead, use CHOOSE CASE or IF statements for the property names that need special handling.
For example, in the PropertyChanged event, this code checks for three specific properties and gets their new value when they are the property that changed. The value is assigned to a variable of the appropriate datatype:
integer li_index, li_minvalue long ll_color CHOOSE CASE Lower(PropertyName) CASE "value" li_index = ole_1.Object.Value CASE "minvalue" li_minvalue = ole_1.Object.MinValue CASE "backgroundcolor" ll_color = ole_1.Object.BackgroundColor CASE ELSE ... // Other processing END CHOOSE
In some cases the value of the PropertyName argument is an empty string (""). This means a more general change has occurred—for example, a change that affects several properties.
If the OLE server does not support property change notification, then the PropertyRequestEdit and PropertyChanged events are never triggered, and scripts you write for them will not run. Check your OLE server documentation to see if notification is supported.
If notifications are not supported and your application needs to know about a new property value, you might write your own function that checks the property periodically.
For more information about the PropertyRequestEdit and PropertyChanged events, see the PowerScript Reference.
