Use of Finalize/Dispose method in C#

Question

C# 2008

I have been working on this for a while now, and I am still confused about the use of finalize and dispose methods in code. My questions are below:

Answer 1

The recommended IDisposable pattern is here. When programming a class that uses IDisposable, generally you should use two patterns:

When implementing a sealed class that doesn't use unmanaged resources, you simply implement a Dispose method as with normal interface implementations:

public sealed class A : IDisposable
{
    public void Dispose()
    {
        // get rid of managed resources, call Dispose on member variables...
    }
}

When implementing an unsealed class, do it like this:

public class B : IDisposable
{    
    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    protected virtual void Dispose(bool disposing)
    {
        if (disposing)
        {
            // get rid of managed resources
        }   
        // get rid of unmanaged resources
    }

    // only if you use unmanaged resources directly in B
    //~B()
    //{
    //    Dispose(false);
    //}
}

Notice that I haven't declared a finalizer in B; you should only implement a finalizer if you have actual unmanaged resources to dispose. The CLR deals with finalizable objects differently to non-finalizable objects, even if SuppressFinalize is called.

So, you shouldn't declare a finalizer unless you have to, but you give inheritors of your class a hook to call your Dispose and implement a finalizer themselves if they use unmanaged resources directly:

public class C : B
{
    private IntPtr m_Handle;

    protected override void Dispose(bool disposing)
    {
        if (disposing)
        {
            // get rid of managed resources
        }
        ReleaseHandle(m_Handle);

        base.Dispose(disposing);
    }

    ~C() {
        Dispose(false);
    }
}

If you're not using unmanaged resources directly (SafeHandle and friends doesn't count, as they declare their own finalizers), then don't implement a finalizer, as the GC deals with finalizable classes differently, even if you later suppress the finalizer. Also note that, even though B doesn't have a finalizer, it still calls SuppressFinalize to correctly deal with any subclasses that do implement a finalizer.

When a class implements the IDisposable interface, it means that somewhere there are some unmanaged resources that should be got rid of when you've finished using the class. The actual resources are encapsulated within the classes; you don't need to explicitly delete them. Simply calling Dispose() or wrapping the class in a using(...) {} will make sure any unmanaged resources are got rid of as necessary.