Changes on items in report events are not applied

AUTHOR: Stephania Tapela

DATE POSTED: October 25, 2016

PROBLEM
Changes on items in report events are not applied.

In Telerik Reporting versions prior to R3 2016, all changes in events were accepted, even these applied on items' definitions. When items' definitions are modified in events, changes are applied on all consecutive processing elements with an expected result.

Modifying report in events prior to R3 2016:

As of R3 2016 we applied an optimization change in the report rendering algorithm and now each definition item property values are read and cached once the report rendering starts.
If you are working with item definitions in events, they will not be modified. For more details, check the updated Understanding Events help article.

Modifying report in events after R3 2016:

Note that in Report NeedDataSource and ItemDataBinding events the processing instances of the other report items are not created yet. Hence, it is not possible to modify other items in these Report events.
Modifying other items in events after R3 2016:

SOLUTION 

In general, in all versions changes in events are possible if they are applied on the processing elements, not the items' definitions (report elements accessible through this. in C# or Me. in VB.NET). The valid approaches are illustrated in Accessing Report Items Programmatically.

The recommended approach is to use the expression engine and avoid custom code in events:

1. Conditional Formatting to control styles via expressions;
2. Bindings to set properties of items via expressions;
3. User functions to set properties of items, when the built-in functions are not sufficient.

The usage of the expression engine assures items will be modified at the right moment.

Interesting help articles related to binding data via expressions and modifying reports:

• How to use the ReportItem.DataObject property in expressions
• How to Databind to Collection Properties
• How to bind Sub Report to Main Report's Data
• Change Sub Report based on Main Report's Data
• Changing the connection string dynamically according to runtime data (the same approach can be used if you need to change data sources and to modify the report structure at run-time).

Note: if you have many legacy reports and changing the code in events in all of them is not an option, you could give up on the property resolution optimization and turn it off.
To do so, apply the following settings in Telerik.Reporting configuration section in application configuration file: