共用方式為

IsDBNull Function 

  • 發行項

Returns a Boolean value indicating whether an expression evaluates to the System.DBNull class.

Public Function IsDBNull(ByVal Expression As Object) As Boolean

Parameters

  • Expression
    Required. Object expression.

Remarks

IsDBNull returns True if the data type of Expression evaluates to the DBNull type; otherwise, IsDBNull returns False.

The System.DBNull value indicates that the Object represents missing or nonexistent data. DBNull is not the same as Nothing, which indicates that a variable has not yet been initialized. DBNull is also not the same as a zero-length string (""), which is sometimes referred to as a null string.

Example

This example uses the IsDBNull function to determine if a variable evaluates to DBNull.

Dim testVar As Object
Dim nullCheck As Boolean
nullCheck = IsDBNull(testVar)
testVar = ""
nullCheck = IsDBNull(testVar)
testVar = System.DBNull.Value
nullCheck = IsDBNull(testVar)
' The first two calls to IsDBNull return False; the third returns True.

Requirements

Namespace: Microsoft.VisualBasic

Module: Information

Assembly: Visual Basic Runtime Library (in Microsoft.VisualBasic.dll)

See Also

Reference

IsArray Function (Visual Basic)
IsDate Function (Visual Basic)
IsError Function
IsNothing Function
IsNumeric Function (Visual Basic)
IsReference Function
Object Data Type
TypeName Function (Visual Basic)
DBNull