Working with a list of variables

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
    property Name: String; // 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 Add: TfrxVariable;

    // Adds a variable to the given position of the list
    function Insert(Index: Integer): TfrxVariable;

    // Returns the index of a variable with the given name
    function IndexOf(const Name: String): Integer;

    // Adds a variable to the specified category
    procedure AddVariable(const ACategory, AName: String; const AValue: Variant);

    // Deletes a category and all its variables
    procedure DeleteCategory(const Name: String);

    // Deletes a variable
    procedure DeleteVariable(const Name: String);

    // Returns the list of categories
    procedure GetCategoriesList(List: TStrings; ClearList: Boolean = True);

    // Returns the list of variables in the specified category
    procedure GetVariablesList(const Category: String; List: TStrings);

    // The list of variables
    property Items[Index: Integer]: TfrxVariable readonly;

    // Values of variables
    property Variables[Index: String]: Variant; default;
  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