Object Data Type - Visual Basic (original) (raw)
Holds addresses that refer to objects. You can assign any reference type (string, array, class, or interface) to an Object variable. An Object variable can also refer to data of any value type (numeric, Boolean, Char, Date, structure, or enumeration).
The Object data type can point to data of any data type, including any object instance your application recognizes. Use Object when you do not know at compile time what data type the variable might point to.
The default value of Object is Nothing (a null reference).
Data Types
You can assign a variable, constant, or expression of any data type to an Object variable. To determine the data type an Object variable currently refers to, you can use the GetTypeCode method of the System.Type class. The following example illustrates this.
Dim myObject As Object
' Suppose myObject has now had something assigned to it.
Dim datTyp As Integer
datTyp = Type.GetTypeCode(myObject.GetType())
The Object data type is a reference type. However, Visual Basic treats an Object variable as a value type when it refers to data of a value type.
Storage
Whatever data type it refers to, an Object variable does not contain the data value itself, but rather a pointer to the value. It always uses four bytes in computer memory, but this does not include the storage for the data representing the value of the variable. Because of the code that uses the pointer to locate the data, Object variables holding value types are slightly slower to access than explicitly typed variables.
Programming Tips
- Interop Considerations. If you are interfacing with components not written for the .NET Framework, for example Automation or COM objects, keep in mind that pointer types in other environments are not compatible with the Visual Basic
Objecttype. - Performance. A variable you declare with the
Objecttype is flexible enough to contain a reference to any object. However, when you invoke a method or property on such a variable, you always incur late binding (at run time). To force early binding (at compile time) and better performance, declare the variable with a specific class name, or cast it to the specific data type.
When you declare an object variable, try to use a specific class type, for example OperatingSystem, instead of the generalizedObjecttype. You should also use the most specific class available, such as TextBox instead of Control, so that you can access its properties and methods. You can usually use the Classes list in the Object Browser to find available class names. - Widening. All data types and all reference types widen to the
Objectdata type. This means you can convert any type toObjectwithout encountering a System.OverflowException error.
However, if you convert between value types andObject, Visual Basic performs operations called boxing and unboxing, which make execution slower. - Type Characters.
Objecthas no literal type character or identifier type character. - Framework Type. The corresponding type in the .NET Framework is the System.Object class.
Example
The following example illustrates an Object variable pointing to an object instance.
Dim objDb As Object
Dim myCollection As New Collection()
' Suppose myCollection has now been populated.
objDb = myCollection.Item(1)