Custom Aggregate Functions
- 2 minutes to read
Total summaries provide five predefined aggregate functions. These functions allow you to calculate:
- the number of records
- the maximum and minimum values
- the sum and the average value
ASPxVerticalGrid provides the ASPxGridBase.CustomSummaryCalculate event that enables you to implement custom aggregate functions or calculate summary values using a custom algorithm. Custom summaries allow you to:
- calculate summaries against records that meet specific criteria
- involve multiple data fields in calculations
- implement complex summary functions (e.g., the standard deviation of a population), etc.
To calculate a summary manually:
- create a summary item and set its ASPxSummaryItemBase.SummaryType property to SummaryItemType.Custom
- implement the summary calculation algorithm within the ASPxGridBase.CustomSummaryCalculate event
The ASPxGridBase.CustomSummaryCalculate event fires for each record involved in summary calculation; when calculating a total summary value, the event is raised for each record; to enable you to perform any initialization and finalization, the event is raised before and after the processing of records
The summary calculation consists of three stages.
The CustomSummaryCalculate event is raised once and the SummaryProcess property is set to CustomSummaryProcess.Start. At this stage, you can initialize summary values (e.g., reset internal counters).
The CustomSummaryCalculate event fires multiple times, once for each record in a grid. The SummaryProcess property is set to CustomSummaryProcess.Calculate. At this stage you should accumulate summaries.
The event parameter properties allow the processed record and its values to be obtained.
The CustomSummaryCalculate event is raised once and the SummaryProcess property is set to CustomSummaryProcess.Finalize. At this point, calculate a final summary value and assign it to the event parameter’s TotalValue property.
To determine the current stage, use the event parameter’s SummaryProcess property.
To skip the Calculation stage and calculate a custom summary at the Initialization or Finalization stage, set the event parameter’s TotalValueReady property to
true at the Initialization stage. This automatically skips the Calculation stage and the Finalization stage starts immediately.