1. OnCalc: Use the OnCalc event handler when you want to perform calculations. The OnCalc event essentially only fires once for each record traversal during report generation ensuring correct calculations.
2. OnGetText: The OnGetText event fires each time the component's Text property is referenced. This enables you to override the value of the Text property. You should not make calculations in this event.
3. OnPrint: The OnPrint event fires before the component prints. Use the OnPrint event when you want to dynamically control the appearance of the report component. You should not make calculations in this event.
Please see the ReportBuilder help for more information and examples on all the events associated with the TppVariable class.
Calculations can be done either on the data access side or within ReportBuilder.
When designing reports there are always decisions to be made as to how much processing to do on the data side versus the report side. Usually doing more on one side can greatly simplify the other. So it is often a personal choice based on the power and flexibility of the data and report tools being used.
DataAccess ----------
a. Use SQL - using SQL you can perform many common calculations:
example: Select FirstName + ' ' + LastName As FullName, Quantity * Price AS Cost,
b. Delphi TDataSets enable you to create a calculated TField object and use the DataSet.OnCalcFields event
c. Perform any amount of data processing, summarizing, massaging etc. to build a result set (query or temp table) to feed to the report.
ReportBuilder -------------
Calculations in ReportBuilder are performed primarily using the TppVariable component.
a. Set the Variable.DataType
b. Code the calculations using the Variable.OnCalc event.
c. Use the Timing dialog to control the timing of the OnCalc event. To access the Timing dialog, right click over the Variable component and select the Timing... option from the speed menu.
d. Set the LookAhead property to True, when you need to display summary calculations in the title, header, group header, etc.
e. To perform calculations based on the results of other calculations use the Calc Order dialog of the band. To access the Calc Order dialog, right click over the Band component and select the Calc Order... option from the speed menu.
By using TppVariable components ReportBuilder will take care of caching intermediate results of accumlated calcs that cross pages.
There are a number of calculation examples in the main demos.dpr project.
---
Additional Notes:
1. Do NOT use Band.BeforePrint or Band.AfterPrint. These events fire multiple times and therefore should not be used for calculations.
2. Do NOT store results in variables that exist outside of the reports. For example - form level variables.
Comments
1. OnCalc: Use the OnCalc event handler when you want to perform
calculations. The OnCalc event essentially only fires once for each record
traversal during report generation ensuring correct calculations.
2. OnGetText: The OnGetText event fires each time the component's Text
property is referenced. This enables you to override the value of the Text
property. You should not make calculations in this event.
3. OnPrint: The OnPrint event fires before the component prints. Use the
OnPrint event when you want to dynamically control the appearance of the
report component. You should not make calculations in this event.
Please see the ReportBuilder help for more information and examples on all
the events associated with the TppVariable class.
------------------------------------------------------------------------
TECH TIP: Performing Calculations
------------------------------------------------------------------------
Calculations can be done either on the data access side
or within ReportBuilder.
When designing reports there are always decisions to be made as to
how much processing to do on the data side versus the report side.
Usually doing more on one side can greatly simplify the other. So it is
often a personal choice based on the power and flexibility of the data
and report tools being used.
DataAccess
----------
a. Use SQL - using SQL you can perform many common calculations:
example: Select FirstName + ' ' + LastName As FullName,
Quantity * Price AS Cost,
b. Delphi TDataSets enable you to create a calculated TField object
and use the DataSet.OnCalcFields event
c. Perform any amount of data processing, summarizing, massaging
etc. to build a result set (query or temp table) to feed to the report.
ReportBuilder
-------------
Calculations in ReportBuilder are performed primarily using
the TppVariable component.
a. Set the Variable.DataType
b. Code the calculations using the Variable.OnCalc event.
c. Use the Timing dialog to control the timing of the OnCalc event.
To access the Timing dialog, right click over the Variable
component and select the Timing... option from the speed menu.
d. Set the LookAhead property to True, when you need to display
summary calculations in the title, header, group header, etc.
e. To perform calculations based on the results of other
calculations use the Calc Order dialog of the band. To access
the Calc Order dialog, right click over the Band component
and select the Calc Order... option from the speed menu.
By using TppVariable components ReportBuilder will take care of caching
intermediate results of accumlated calcs that cross pages.
There are a number of calculation examples in the main demos.dpr
project.
---
Additional Notes:
1. Do NOT use Band.BeforePrint or Band.AfterPrint. These events fire
multiple times and therefore should not be used for calculations.
2. Do NOT store results in variables that exist outside of the reports.
For example - form level variables.
--
Nico Cizik
Digital Metaphors
http://www.digital-metaphors.com