function IsValid ()

Function: Checks whether an object variable has been instantiated, that is, whether the value of the instance variable is a valid object handle.

Syntax: IsValid (objectname)

Parameter: ObjectName: The name of the object to check.

return value: Boolean. If the specified object has already created an instance of the case, then the IsValid () function returns True, otherwise false is returned. If the value of the parameter obejctname is null,isvalid () the function returns NULL.

function IsValid ()