IDisposable Question

Question

Say I have the following:

public abstract class ControlLimitBase : IDisposable 
{
}

public abstract class UpperAlarmLimit : ControlLimitBase 
{
}

public class CdsUpperAlarmLimit : UpperAlarmLimit 
{
}

Two Questions:

1. I'm a little confused on when my IDisposable members would actually get called. Would they get called when an instance of CdsUpperAlarmLimit goes out of scope?

2. How would I handle disposing of objects created in the CdsUpperAlarmLimit class? Should this also derive from IDisposable?

Answer 1

Dispose() is never called automatically - it depends on how the code is actually used.

1.) Dispose() is called when you specifically call Dispose():

myAlarm.Dispose();

2.) Dispose() is called at the end of a using block using an instance of your type.

using(var myAlarm = new CdsUpperAlarmLimit())
{

}

The using block is syntactic sugar for a try/finally block with a call to Dispose() on the object "being used" in the finally block.

Answer 2

1. No, IDisposable won't be called just automatically. You'd normally call Dispose with a using statement, like this:

   using (ControlLimitBase limit = new UpperAlarmLimit())
   {
       // Code using the limit
   }
   

   This is effectively a try/finally block, so Dispose will be called however you leave the block.

2. CdsUpperAlarmLimit already implements IDisposable indirectly. If you follow the normal pattern for implementing IDisposable in non-sealed classes, you'll override void Dispose(bool disposing) and dispose your composed resources there.

Note that the garbage collector does not call Dispose itself - although it can call a finalizer. You should rarely use a finalizer unless you have a direct handle on unmanaged resources though.

To be honest, I usually find it's worth trying to change the design to avoid needing to keep hold of unmanaged resources in classes - implementing IDisposable properly in the general case is frankly a pain. It's not so bad if your class is sealed (no need for the extra method; just implement the Dispose() method) - but it still means your clients need to be aware of it, so that they can use an appropriate using statement.