Answer.

Memory management is a key aspect when working with objects in Visual Basic, especially if the application uses resources that require manual release: files, database connections, or external objects.

Background of the Issue

In classic VB (VB6), resources were manually released by calling Set obj = Nothing. In .NET (VB.NET), there is an automatic garbage collector that cleans up unused objects. However, not all memory release happens automatically, especially for unmanaged resources.

The Problem

The automatic garbage collector frees up memory from .NET objects but does not know how to timely reclaim external or manual resources (file descriptors, connections, streams). Neglecting these details leads to memory leaks and resource locking.

The Solution

To correctly free external resources, the IDisposable interface and the Using...End Using statement should be used, ensuring deterministic disposal.

Example code:

' Guaranteed release of file descriptor
Using reader As New StreamReader("data.txt")
    Dim content As String = reader.ReadToEnd()
    ' ... data processing ...
End Using

' For objects that do not support IDisposable, manual release:
Dim obj As SomeComObject = New SomeComObject()
' ... usage ...
System.Runtime.InteropServices.Marshal.ReleaseComObject(obj)
obj = Nothing

Key features:

The garbage collector only releases .NET objects (managed).
For external resources, the use of Using blocks or manual Dispose calls is mandatory.
After releasing the resource, assign Nothing to the variable (for COM objects).

Tricky Questions

If Using is not used for FileStream, will the resource still be released by the GC?

No, the release will occur at an undefined moment. A file lock and resource leak may occur.

Is calling Set obj = Nothing equivalent to calling Dispose()?

No, Set obj = Nothing only removes the reference but does not guarantee immediate release of resources. Dispose() or Using is the only correct way for deterministic disposal.

Is it necessary to call Dispose for objects inheriting from DataSet/DataTable?

Yes, although they are freed by the GC, many associated resources (e.g., database connections) require manual Dispose or Using calls, especially for DataAdapter, Connection, Command.

Common Mistakes and Anti-Patterns

Lack of Using/Dispose when dealing with streams, connections, file descriptors.
Ignoring the need for Marshal.ReleaseComObject when working with COM.
Hoping for the garbage collector to quickly release all types of resources.

Real-Life Example

Negative Case

Reading data from a large file without Using, without Dispose. After some time, the application cannot open a new file: "File is in use by another process".

Pros:

Simple and fast prototype.

Cons:

Descriptor leaks.
File locking.

Positive Case

Opening a connection to a database or file through Using. Retrieving, processing data, and automatic resource release.