The value for a property of a report item can be a literal value, or it can be derived from an expression that is written using the RTL Expressions language. RTL Expressions allow you to define runtime values for any property of a report item, except for those properties that display a specific set of valid values in a dropdown listbox.
Enter an expression in a field of the Properties View, by clicking the Value field. To enter longer values, or obtain hints while typing the entry, click the f(x) button of the desired property to open the RTL Expression Editor:
Figure 1. Edit Expression dialog
The acceptable choices for the next character are displayed as you type. If you press Ctrl Space while entering an expression, a Code Completion box appears containing a list of the valid choices based on the context.
RTL Expressions:
- are typed - an expression is composed of items of different types and the expression returns a particular type. The properties in the Properties View are also typed. Any expression entered as a value for a property must return the specified type. For example, the text property of a WordBox has a type of String. So, any RTL expression for the text property is expected to yield a String. See Report Element Properties for a list of each report property and its type.
- closely follow the Java™ syntax for expressions. The main difference is that the "new" keyword is not supported, so that it is not possible to create and subclass objects. RTL Expressions loosely follow the Java evaluation semantics (operator precedence, evaluation order, etc.).
- can use 4GL variables. The 4GL variable is converted to a specific type within the expression (See Conversion table) .
RTL Classes provide member functions (methods) and member variables that you can use in your expressions. There is a class for each type of a form property.