Friendly reminds, there is a mistake in translation of this article, please be sure to combine comments to see this translation! ISNOT operator
Isnot is
The antisense operator of IS. Before you reference an object, you must check if it has been initialized, and in the past, we have used this way to use this very important way:
IF
Not myobj
Is nothing then
IsNot allows you to do direct comparison, else to use
NOT operator's troubles:
IF myobj
ISNOT
Nothing then
Similarly, you don't have to use two object instances or if you do not use it.
NOT operator:
IF myobj1
ISNOT MYOBJ2
THEN
Don't see this is just a simple change.
IsNot makes up for a shortcoming of Visual Basic language consistency, your code will become more concise.
TRYCAST statement
In Visual Basic 2003, you can use the following two methods to convert the type of object to another type:
DIM P
As products
P =
CType (Obj, Product)
P =
Directcast (Obj, Product)
Above, you are using
CType converts a type to another, and
DirectCast requires that there is an inheritance or implementation of the interface between the two objects (the instructions here)
mistaken:
CType and
The actual difference between Directcast is
DirectCast requires the same type of time when the object is the same as the specified conversion type, and
The operating efficiency of CType is slightly lower, and 淌 注). But the problem here is that no matter which method you use, if the OBJ cannot be converted or cast (the conversion is "convert", the cast is "cast", the author confuses the difference between Convert and Cast in some places, in fact, their difference Be
CType and
Directcast difference. But the author believes that there is no need to go to this word, so I am unified in other places to "convert", 淌 注) as a product type, then the runtime will result in an exception.
Use new
TRYCAST statement. It and
CType or
The way Directcast is the same, but it will return if the type conversion cannot be completed.
Nothing value to the object:
P =
Trycast (Obj, Product)
IF P
ISNOT Nothing
THEN
'Use P objects ...
END IF
