Programming Excel with VBA and .NET

Check Results

In many situations, you need to check the result of an operation to tell if it succeeded. The result-checking functions in Visual Basic let you test results before you take actions that might otherwise cause an error. Table 3-16 lists the result-checking functions.

Table 3-16. Visual Basic result-checking functions

Category	Function	Use to
Boolean tests	IsArray	Tell if a variable is an array
	IsDate	Tell if a variable contains data that can be converted to a Date
	IsEmpty	Tell if a variable has not yet been initialized
	IsError	Tell if a variable contains an Error object
	IsMissing	Tell if a ParamArray argument was omitted
	IsNull	Tell if a variable contains no valid data
	IsNumeric	Tell if a variable contains a value that can be converted to a number
	IsObject	Tell if a variable is a reference to a valid object
Type tests	TypeName	Get the name of the variable’s type as a string
	TypeOf	Test the type of a variable within an If block
	VarType	Get the variable’s type as a VbVarType constant

Most of these tests are used with variables that were declared as Variant or Object data types. Those types of variables can contain many different kinds of data, so it is often necessary to test what the variable contains before proceeding in code.

There are several common uses of this in Excel. The first is ActiveSheet.property, which may refer to a Worksheet, Chart, or other object:

 Sub ChangeSheets( ) Select ...