IsNothing 函数

返回一个 Boolean 值，指示表达式是否未被指派对象。

Public Function IsNothing(ByVal Expression As Object) As Boolean

参数
Expression 
必选项。Object 表达式。 
备注
如果表达式表示尚未被指派任何对象的 Object 变量，IsNothing 函数返回 True；否则，返回 False。
示例
下面的示例使用 IsNothing 函数来确定对象变量是否与任何对象实例相关联。
Dim MyVar As Object   ' No instance assigned to this variable yet.
Dim MyCheck As Boolean
' ...
MyCheck = IsNothing(MyVar)   ' Returns True.
' ...
MyVar = "ABCDEF"   ' Assign a string instance to the variable.
MyCheck = IsNothing(MyVar)   ' Returns False.
' ...
MyVar = Nothing   ' Disassociate the variable from any instance.
MyCheck = IsNothing(MyVar)   ' Returns True.