Automating Microsoft Access with VBA

Using the Is Functions for Flawless Processing

All functions are prone to errors if you don't reference the right type of data. Most of these errors can be avoided by a simple check using one of VBA's many Is functions:

• IsArray Tests for an array

• IsDate Tests for a valid date value

• IsEmpty Determines whether variable has been initialized (by having stored a value)

• IsError Determines whether an expression is a valid error value

• IsMissing Determines whether an optional argument has been passed to a procedure

• IsNull Determines whether an expression contains a Null value

• IsNumeric Determines whether an expression can be evaluated as a valid number

• IsObject Indicates whether a variable contains a reference to an object

You learn about arrays in Chapter 7, "Working with Arrays," (p. 105).

All the Is functions use the same simple form

Isfunction(value)

where value represents the actual value, variable, argument, or expression being checked. Each function returns a Boolean value. If the value meets the condition being checked for the function returns True. Each function returns a False value if the condition isn't met. For instance, if the variable varValue is Null, the following function returns True:

IsNull(varValue)