How to: Dispose of a System Resource (Visual Basic)

You can use a Using block to guarantee that the system disposes of a resource when your code exits the block. This is useful if you are using a system resource that consumes a large amount of memory, or that other components also want to use.

To dispose of a file stream when your code is finished with it

1. Make sure you include the appropriate Imports Statement (.NET Namespace and Type) for the file stream at the beginning of your source file (in this case, System.IO).

2. Create a Using block with the Using and End Using statements. Inside the block, put the code that deals with the file stream.

3. Declare the stream and create an instance of it as part of the Using statement.

   ' Insert the following line at the beginning of your source file.  
   Imports System.IO  
   Public Sub AccessFile(ByVal s As String)  
       Using fs As New StreamReader(s)
           MsgBox("reading file contents """ & fs.ReadToEnd() & """")  
       End Using  
   End Sub
   

   The system disposes of the resource no matter how you exit the block, including the case of an unhandled exception.

   Note that you cannot access fs from outside the Using block, because its scope is limited to the block.

   You can use this same technique on a system resource such as a SQL database connection or a COM wrapper. You use a Using block when you want to be sure to leave the resource available for other components after you have exited the Using block.

See also

• Control Flow
• Decision Structures
• Loop Structures
• Other Control Structures
• Nested Control Structures
• Using Statement