VB is a piece of cake--------early binding and late binding

Early binding and late binding Visual Studio 2005Other versions

When an object is assigned to an object variable, the Visual Basic compiler executes a process called binding. If an object is assigned to a variable declared as a specific object type, the object is early bound. Early bound objects allow the compiler to allocate memory and perform other optimizations before the application executes. For example, the following code fragment declares a variable to be of type FileStream:

Vb

'  Create a variable to hold a new object. Dim FS as System.IO.FileStream ' Assign a new object to the variable. FS = New System.IO.FileStream ("C:\tmp.txt", _    System.IO.FileMode.Open)

Because FileStream is a specific type of object, an instance assigned to FS is an early binding.

Conversely, if an object is assigned to a variable declared as object type, the object is late-bound. Objects of this type can store references to any object, but there are many advantages to early-bound objects. For example, the following code snippet declares an object variable to store the object returned by the CreateObject function:

Vb

' To use this example, you must has Microsoft Excel installed on your computer. ' Compile with Option Strict Off to allow late binding. Sub testlatebinding ()    Dim xlapp As Object    Dim Xlbook As Object    Dim xlsheet As Object    xlapp = CreateObject ( "Excel.Application")    ' late bind an instance of an Excel workbook.    Xlbook = XlApp.Workbooks.Add    ' Late bind an instance of an Excel worksheet.    Xlsheet = xlbook.worksheets (1)    xlsheet.activate ()    ' Show the application.    xlSheet.Application.Visible = True    ' Place some text in the second row of the sheet.    Xlsheet.cells (2, 2) = "This is column B row 2" End Sub

Benefits of early binding

Early bound objects should be used whenever possible, because they allow the compiler to make important optimizations to produce more efficient applications. Early-bound objects are much faster than late-bound objects and can make code easier to read and maintain by declaring the kind of objects they use. Another advantage of early binding is that it enables useful features such as automatic code completion and dynamic Help, because the Visual Studio integrated Development Environment (IDE) can determine exactly what type of object you are using when you edit your code. Because early binding allows the compiler to report errors when compiling a program, it reduces the number and severity of run-time errors.

Attention
Late binding can only be used to access a type member that is declared public. Accessing a member that is declared as friend or Protected friend causes a run-time error.

VB is a piece of cake--------early binding and late binding