"MyBase" and "MyClass" Usage in VB.NET
In what scenarios would one use the
MyClass keywords in VB.NET?
MyBase is used when a virtual function needs to call its parent’s version. For example, consider:
Class Button Public Overridable Sub Paint() ' Paint button here. ' End Sub End Class Class ButtonWithFancyBanner Inherits Button Public Overrides Sub Paint() ' First, paint the button. ' MyBase.Paint() ' Now, paint the banner. … ' End Sub End Class
(This is the same as
base in C#.)
MyClass is rarely used at all. It calls the own class’s method, even if it would usually call the derived class’s virtual method. In other words, it disbands the virtual method dispatching and instead makes a static call.
This is a contrived example. I’m hard-pressed to find a real-world usage now (although that certainly exists):
Class Base Public Overridable Sub PrintName() Console.WriteLine("I’m Base") End Sub Public Sub ReallyPrintMyName() MyClass.PrintName() End Sub End Class Class Derived Inherits Base Public Overrides Sub PrintName() Console.WriteLine("I’m Derived") End Sub End Class ' … Usage: ' Dim b As Base = New Derived() b.PrintName() ' Prints "I’m Derived" ' b.ReallyPrintMyName() ' Prints "I’m Base" '
(This doesn’t exist in C#. In IL, this issues a
call instead of the usual
Both are used when you need to call an virtual method and you need to specify which one.
MyBase will call the method in the base class,
MyClass will call the method in the current class.
I don't think I've used
MyClass more than once or twice, but
MyBase I've used quite a bit when I override a method but want the code in the overridden method to be executed as well.
mybase refers to the immediate base class of the current instance.
myclass refers to the current instance, but ignores any overridden implementation of the properties/methods of the class.
Regarding the usage of MyClass, there is a very minor speed improvement to be had if you're using
MyClass inside of a leaf class (NotInheritable class). Specifically, if there is some method that exists in a parent class and is not overridden OR exists as an override in the leaf class, then using
MyClass instead of
Me causes a
call opcode to be used instead of
MyBase, which also emits the
call opcode, isn't applicable in this case where you want the method to be invoked regardless if it's implemented/overridden in the leaf or existing only in the parent. I.e., you're maintaining a form of style consistency among a large number of similar objects.
And when I say "speed improvement", I'm talking a paltry ~5ms out of 100,000 runs on a low-end development server running in 32bit mode, on a string-parsing function. Or to state it another way, the faster the machine, the smaller this difference is going to be. But, I wanted to put it out there.
These keywords are used in scenarios involving Inheritence. MyBase, MyClass are often used to refer to some functionality or property in the parent class. If you have a class that derives from another, those keywords are used to reference code in the context of the parent class.