• Article

Expression Dialog Box

Use the Expression dialog box to write Microsoft Visual Basic expressions for report item properties. You can use expressions to set many properties, including color, font, and borders. At run time, the report processor evaluates expressions and substitutes the result for the value of the property.

Expressions can be simple or complex. You can type simple expressions directly in a text box on the design surface or in a dialog box. To create complex expressions, use the Expression dialog box. For more information, see Understanding Simple and Complex Expressions (Reporting Services).

To open the Expression dialog box, click the Expression (fx) button in dialog boxes, or select Expression from the shortcut menu or drop-down lists in the Properties pane. For more information, see Understanding Simple and Complex Expressions (Reporting Services).

Some dialog boxes (for example, Dataset Properties Dialog Box, Filters) allow you to create multiple expressions that are combined during report processing, but the Expression dialog box works with a single expression at a time.

The Expression dialog box includes a code window, category tree, category items, description pane, and example pane.

The Expression dialog box is context-sensitive; the category items and descriptions change in response to the expression category you are working with. It supports IntelliSense, statement completions, function call examples, and syntax coloring to help you detect syntax errors.

For more information, see How to: Add an Expression (Reporting Services), Expression Examples (Reporting Services), and Using Parameters Collection References in Expressions (Reporting Services).

Expression Constructs

Expressions begin with an equal sign (=) and can include constants, literals, operators, and references to built-in fields, built-in collections, built-in functions, Visual Basic run-time library functions, .NET Framework common language runtime classes, and custom functions. The following list describes the categories and values you can add to an expression. 

  • Set expression for: <PropertyName>
    The name of the property that you are defining an expression for. You can also set this property, by name, in the Properties pane.

  • Constants
    Provides a list of predefined values valid for this property for properties that are based on constants. For example, a property based on color shows valid color names. For a property that is a Boolean data type, values are True and False.

    Not all items that support expressions can be set to a constant. If a property cannot be set to constant value, the description pane provides this information.

  • Built-in Fields
    Provides a list of the items in the global collection that you can use in an expression. Some collections are only supported after the report is published to the server. For more information, see Using Built-in Collections in Expressions (Reporting Services).

  • Parameters
    Provides a list of report parameters.

  • Fields(<selected Dataset>)
    Displays the list of fields for the dataset selected in the Datasets category. Double-click a field to copy the field to the Expression box.

  • Datasets
    Provides a list of available datasets and shows the fields that are members of the dataset.

  • Variables
    Displays a list of report variables. For more information, see Using Report and Group Variables Collection References in Expressions (Reporting Services).

  • Operators
    Displays the operators you can include in a calculation or string manipulation. For more information, see Using Operators in Expressions (Reporting Services).

  • Common Functions
    Displays common functions, grouped by type. When you select a function in the Item pane, a description and example appear.

    Common functions include built-in report and aggregate functions, Visual Basic run-time library functions, and .NET Framework common language runtime classes (CLR) in the Math and Convert namespace. You can also add references to CLR classes and external assemblies that do not appear in the category list. For more information, see Using Common Function and Assembly References (Reporting Services).

Options

  • Code window
    Use the code window in the top pane to type an expression. When you open the Expression dialog box, the code window contains the expression. You can replace or revise the expression. You can add function calls, operators, constants, fields, parameters, items from the global collections, and references to custom code. The code window displays your changes as you make them.

    A wavy red underline indicates a syntax error. Hover over the underlined text to see the error message.

    When you type in global collection terms followed by a punctuation separator, you will see a drop-down list of available members or properties. From the drop-down list, you can type the first few characters followed by a tab to automatically fill the selection.

    When you type in a function name followed by a left parenthesis, you will see a tooltip that provides information about the parameters and function return values.

  • Category
    Displays categories of expressions. Choosing a category establishes a context for creating an expression and changes the list of valid values in the Item pane. For example, for an expression for a text box value, expand Common functions and select Aggregate functions to display Avg, Count, and other functions in the Item pane.

  • Item
    Displays the list of valid values for the selected category. Double-click on an item to add the expression text for this item at the insertion point in the code window.

  • Values
    Depending on the category and item you select, the third pane contains a description, a sample expression, or a list of valid values. Drag the edge of the dialog box to widen the sample area.