Why We Should Prefer To Use Dispose Method Than Finalize Method

It is always recommended to use Dispose method to clean unmanaged resources. You should not implement the Finalize method until it is extremely necessary. At runtime C#, C++ destructors are automatically converted to Finalize method.

.NET Garbage collector does almost all clean up activity for your objects. But unmanaged resources (For example, Windows API created objects, File, Database connection objects, COM objects, etc) is outside the scope of .NET framework we have to explicitly clean our resources. For these types of objects, .NET framework provides Object.Finalize method, which can be overridden and clean up code for unmanaged resources can be put in this section.

Problem with finalize is that garbage collection has to make two rounds in order to remove objects which have finalize methods.

For example, lets say there are three objects: Object1, Object2, and Object3. Object2 has the finalize method overridden and remaining objects do not have the finalize method overridden.

Now when garbage collector runs for the first time it searches for objects whose memory has to free. He can see three objects but only cleans the memory for Object1 and Object3. Object2 it pushes to the finalization queue.

Now garbage collector runs for the second time. The garbage collector gets to know there are no objects to be released and then checks for the finalization queue and at this moment, it clears object2 from the memory.

So if you notice that object2 was released from memory in the second round and not first. That is why the best practice is not to write clean up Non .NET resources in Finalize method rather use the DISPOSE.

Dispose method belongs to ‘IDisposable’ interface. We had seen in the previous section how bad it can be to override the finalize method for writing the cleaning of unmanaged resources. So if any object wants to release its unmanaged code best is to implement IDisposable and override the Dispose method of IDisposable interface. Now once your class has exposed the Dispose method it is the responsibility of the client to call the Dispose method to do the cleanup.

Use of Dispose Method

To use or override dispose method, implement Idisposable interface in your class that comes under System namespace. The following example is a class that implements IDisposable interface for cleaning object of file.

public class disposeexample: IDisposable
{
    // Flag: Has Dispose already been called?
    bool disposed = false;
    private FileStream filestream;
    private StreamReader streamreader;
    public string ReadFile()
    {
        try
        {
            filestream = new FileStream(Path.Combine(Environment.CurrentDirectory, "TextFile1.txt"), FileMode.Open, FileAccess.Read);
            streamreader = new StreamReader(filestream);
            return streamreader.ReadToEnd();
        }
        catch(Exception ex)
        {
            throw ex;
        }
        finally
        {
            streamreader.Close();
            filestream.Close();
            this.Dispose(true);
        }
    }
    protected virtual void Dispose(bool disposing)
    {
        if(disposed) return;
        if(disposing)
        {
            filestream.Dispose();
            streamreader.Dispose();
        }
        // Free any unmanaged objects here.
        //
        disposed = true;
    }
}

Summary

Hope you must get why we should prefer dispose method.