In ActiveReports, you can use an expression to set the value of a control in the report, or set conditions under which certain styles apply. You can set Microsoft Visual Basic® .NET in expressions through,

• Properties in the properties window
• Expression Editor dialog

All expressions begin with an equal sign (=). Even the expression for a field value for a TextBox is set as follows:

=Fields!LastName.Value

Expression Editor Dialog

You can build expressions quickly using the Expression Editor dialog. This dialog allows you to choose from a number of fields available to the report as well as to a particular property. You can access the Expression Editor by selecting nearly any property of a control and choosing <Expression...> from the drop-down list.

There are the following types of fields available in the Expression Editor:

• Constants
  Constants available for properties which have enumerated values such as TextDecoration or BorderStyle.
• Common Values
  Run time values available to every property in every report. There are two variables in this list which come from the User collection: User ID and User Language. See Common Values for further information.
• Parameters
  Parameters fields available in reports which contain report parameters. If available, you can choose a parameter from this field to retrieve the current value of the parameter.
• Fields (DataSet name)
  All fields from a dataset which is linked to the report control.
• Datasets
  All fields in each dataset associated with the report. However, the report retrieves only the sum or the first value of any field that is not within the current dataset scope.
• Operations
  Arithmetic, comparison, concatenation, logical/bitwise, bit shift operators for creating custom expressions.
• Common Functions
  Predefined Visual Basic .NET functions for which ActiveReports provides intrinsic support. See Common Functions for more information.
• Document Map
  The DocumentMap.Path expression defines labels for the report's TableOfContents members. The example of such expression is =DocumentMap.Path & " General Information". If this expression is defined in the Label property of the report's control associated with the report's TableOfContents, General Information will be displayed as the label of the corresponding report's TableOfContents member.

Create an Expression in the Expression Editor

The Expression Editor dialog is composed of two panes, Fields and Expression.

1. From the Fields pane, select a field you want to use in your expression.
2. Click the Replace, Insert or Append button to add the field to the Expression pane. The expression pane shows the fields in a valid expression format.
3. Click OK to close the dialog.

The expression appears as the property value in the properties grid.

Using Expressions in Reports

In the raw form, your data may not be ideally suited for display in a report. You can customize it and bring it into shape using expressions. Following are some examples of how expressions are set in different scenarios.

Concatenating Fields and Strings

You can concatenate fields with strings and with other fields. For e.g., use the following expression to get a result like Customer Name: Bossert, Lewis.

="Customer Name: " & Fields!LastName.Value & "," & Fields!FirstName.Value

Conditional Formatting

You can use expressions in properties like Color, Font, Border etc. on specific field values based on a condition, to highlight a part of data. The formula for conditional formatting is:
=iif( Fields!YourFieldName.Value operator "Value to compare", "If condition is met, use this value.", "If not, use this one.")

For e.g., if you enter the following expression in the Font > FontWeight property of a textbox that displays names of people, you get the name "Denise" in bold.

=iif(Fields!FirstName.Value = "Denise", "Bold", "Normal")

Functions

You can use a number of aggregate and other functions in your expressions. ActiveReports includes a range of functions, including running value, population standard variance, standard deviation, count, minimum and maximum. For e.g., use the following expression to get a count of employees.

=Count(Fields!EmployeeID.Value, Nothing)

As you design the report, the full text of an expression can get very long. ActiveReports makes expressions easier to read by shortening them.

When an expression is in the form:

=Fields!<FieldName>.Value

On the design surface, you see this text inside that TextBox:

=[<FieldName>]

Double-click the TextBox to view the full expression in edit mode.

For aggregates too, when the Expression value is:

=<Aggregate>(Fields!<FieldName>.Value)

On the design surface, you see this text inside the TextBox:

=<Aggregate>([<FieldName>])

This shortened expression value is only a visual change to allow you to see the field name easily. It shows up in both the TextBox on the design surface as well as any dropdown boxes inside the dialogs. 

Besides the shorthand for field names, you can also type shorthand like [@Param] for parameters and [&Value] for Globals such as [&PageNumber] on the design surface. Please note that you cannot use shorthand in the Expression Editor.

Common Values

Common Values are run time values available to every property in every report. You can directly drag and drop these common values from the Report Explorer onto the design surface or add and modify the values from the Expression Editor. Following is a list of the values that you can see under the Common Values node in the Report Explorer and in the Expression Editor.

Common Functions

You can use a function in an expression to perform actions on data in data regions, groups and datasets. You can access these functions in the Expression Editor dialog. In any property that accepts expressions, you can drop down the property and select <Expression...> to open the dialog.

Within the Expression Editor dialog, there is a tree view of Fields. Expand the Common Functions node to view the available functions. The following tables contain details about each of the functions included in ActiveReports for use in property expressions.

Date & Time

These are all methods from the DateAndTime class in Visual Basic. Please see the msdn DateAndTime Class topic for information on overloads for each method.

These are all the available aggregate functions:

Math

These are all methods and fields from the System.Math class. Please see the msdn Math Class topic for information on overloads for each method.

Inspection

These are all methods from the DateAndTime class in Visual Basic. Please see the msdn DateAndTime Class topic for information on overloads for each method.

ProgramFlow

These are all methods from the Interaction class in Visual Basic. Please see the msdn Interaction Class topic for more information.

Aggregate

You can use aggregate functions within report control value expressions to accrue data. ActiveReports supports aggregate functions from RDLX 2005, plus some proprietary extended set of functions. For all of the functions, you can add an optional <Scope> parameter.

These are all the available aggregate functions:

Conversion

These are all methods from the Convert class in the .NET Framework. Please see the msdn Convert Class topic for more information.

Miscelleneous

ActiveReports also offers several functions which do not aggregate data, but which you can use with an IIf function to help determine which data to display or how to display it.

The first four are miscellaneous functions from the RDLX 2005 specifications. GetFields is a proprietary function to extend RDLX specifications.

'Within the Code tab, add this function.

Public Function DisplayAccountID( flds as Object) as Object

  If flds("FieldType").Value = "ParentAccount" Then

    Return flds("AccountID").Value

  Else

    Return flds("ParentAccountID").Value

  End If

End Function

Using Scope Parameter

All functions have a Scope parameter which determines the grouping, data region, or dataset to be considered when calculating the aggregate or other function. Within a data region, the Scope parameter's default value is the innermost grouping to which the report control belongs. Alternately, you can specify the name of another grouping, dataset, or data region, or you can specify Nothing, which sets it to the outermost data region to which the report control belongs.

The Scope parameter must be a data region, grouping, or dataset that directly or indirectly contains the report control using the function in its expression. If the report control is outside of a data region, the Scope parameter refers to a dataset. If there is only one dataset in the report, you can omit the Scope parameter. If there are multiple datasets, you must specify which one to use to avoid ambiguity.