The notion of variables was minutely explained in the corresponding chapter. Let us briefly call to mind the main points.

A user can specify one or several variables in a report. A value or an expression, which will be automatically calculated when referring to a variable, can be assigned to every variable. Variables can be visually inserted into a report via the “Data tree” window. It is convenient to use variables for aliasing of compound expressions, which are often used in a report.

It is necessary to use the “frxVariables” unit when working with variables.

Variables are represented by the “TfrxVariable” class.

TfrxVariable = class (TCollectionItem)

published

Name of a variable

property Value: Variant;

Value of a variable

end;

The list of variables is represented by the “TfrxVariables” class. It contains all methods necessary for working with the list.

TfrxVariables = class (TCollection)

public

Adds a variable to the end of the list

function Insert(Index: Integer): TfrxVariable;

Adds a variable to the given position of the list

function IndexOf( const Name: String ): Integer;

Returns the index of a variable with the given name

procedure AddVariable( const ACategory, AName: String ; const AValue: Variant);

Adds a variable to the specified category

procedure DeleteCategory( const Name: String );

Deletes a category and all its variables

procedure DeleteVariable( const Name: String );

Deletes a variable

procedure GetCategoriesList(List: TStrings; ClearList: Boolean = True);

Returns the list of categories

procedure GetVariablesList( const Category: String; List: TStrings);

Returns the list of variables in the specified category

property Items[Index: Integer]: TfrxVariable readonly;

The list of variables

property Variables[Index: String]: Variant; default;

Values of variables

end;

If the list of variables is long, it is convenient to group it by categories. For example, when having the following list of variables:

Customer name

Account number

in total

total vat

one can represent it in the following way:

Properties

Customer name

Account number

Totals

In total

total vat

There are the following limitations:

- at least one category must be created

- categories form the first level of the data tree, variables form the second one

- categories cannot be nested

- variables’ names must be unique within a whole list, not within a category