Implementing Idisposable Correctly

Am I implementing IDisposable correctly?

You don't need to use this extensive version of IDisposable implementation if your class doesn't directly use unmanaged resources.

A simple

 public virtual void Dispose()
 {

     _Writer.Dispose();
 }

will suffice.

If your consumer fails to Dispose your object it will be GC'd normally without a call to Dispose, the object held by _Writer will also be GC'd and it will have a finaliser so it still gets to clean up its unmanaged resources properly.

Edit

Having done some research on the links provided by Matt and others I've come to the conclusion that my answer here stands. Here is why:-

The premise behind the disposable implementation "pattern" (by that I mean the protected virtual Dispose(bool), SuppressFinalize etc. marlarky) on an inheritable class is that a sub-class might hold on to an unmanaged resource.

However in the real world the vast majority of us .NET developers never go anywhere near an unmanaged resource. If you had to quantify the "might" above what probabilty figure would you come up with for you sort of .NET coding?

Lets assume I have a Person type (which for sake of argument has a disposable type in one of its fields and hence ought to be disposable itself). Now I have inheritors Customer, Employee etc. Is it really reasonable for me to clutter the Person class with this "Pattern" just in case someone inherits Person and wants to hold an unmanaged resource?

Sometimes we developers can over complicate things in an attempt to code for all possible circumstances without using some common sense regarding the relative probability of such circumstances.

If we ever wanted to use an unmanaged resource directly the sensible pattern would be wrap such a thing in its own class where the full "disposable pattern" would be reasonable. Hence in the significantly large body of "normal" code we do not to have to worry about all that mucking about. If we need IDisposable we can use the simple pattern above, inheritable or not.

Phew, glad to get that off my chest. ;)

Implementing IDisposable correctly on parent classes in C#

Your subclass should override Dispose(bool disposing) if anything - that's the whole point of having that method at all, really.

However, I suspect that the base class will make the right calls anyway, so you shouldn't need to do anything, unless you have extra resources to release which aren't released in Close(). If that's the case, do that in Dispose(bool disposing):

protected override void Dispose(bool disposing)
{
    // Allow the base class to release resources
    base.Dispose(disposing);
    // Release any extra resources here 
}

Note that your current implementation will lead to a StackOverflowException as your two Dispose overloads call each other.

Implementing IDisposable C#

You're on the right track. Anytime you have a class level variable that is disposable the containing class should also be disposable. And you're handling it properly from what I can tell. I don't see class name line so I can't tell if you have the IDisposable interface included but I imagine you do since you have implemented the methods. If not make sure you add it.

IDisposable is a chain reaction type of implementation. If the variable is disposable, and it's only local to a method call then you dispose of it at the end of the call, but if it's at the class level you implement IDisposable and dispose of it with your class as you're doing. That way anyone using your class can dispose of it properly.

So for example: Say I have a file open in my class...

public class MyClass
{
     private File txtFile = File.Create(...)
}

Now someone uses my class.

private void useClass()
{
     var myClass = new MyClass();
}

Well, they have just opened a file and it wasn't disposed of properly.

Modify the code and it can be used like so...

public sealed class MyClass : IDisposable
{
     private File txtFile = new File.Create(...)

     public void Dispose()
     {
          txtFile.Dispose();
          GC.SuppressFinalize(this);
     }

     ~MyClass() => Dispose();
}

And when the use it they can use it like so...

private void useClass()
{
     using (var myClass = new MyClass())
     {
         //some code
     }
}

Hopefully this answers your questions. Just remember, is you declare a disposable object local to a method then you don't have to implement IDisposable in your class because you're going to dispose of it in that method. But if you implement it at class level scope, whether you have a method disposing it or not, you should implement IDisposable and check to make sure it's disposed when that containing class calls dispose. Make sense?
Hope this helps.

false-positive: Fix this implementation of IDisposable to conform to the dispose pattern

I saw that you already fixed the issue, but in case someone else has the same problem, I will elaborate on the rule requirements.

The idea of this rule is to allow potential derived classes to correctly dispose the members of your class. Hence if your class is sealed, the rule assumes your class correctly disposes itself and does nothing (there is another rule, S2931 which checks if your class contains IDisposable fields that need to be disposed).

If the class is not sealed, the rule checks if it has a base class that implements IDisposable. If it has and your class also implements IDisposable, the rule will recommend to remove your implementation (e.g. remove the IDisposable interface from your class) and override the base class's protected Dispose(bool) method.

If the base class does not implement IDisposable, the rule requires a protected virtual Dispose(bool) method (to allow the inheritors to correctly dispose your class).

If your class contains a finalizer, i.e. destructor, the rule checks if its content is a single invocation of Dispose(false).

The rule checks if the content of the Dispose() method (the one from the interface) contains a single invocation of Dispose(true). If your class has a finalizer, the rule requires an additional call to GC.SuppressFinalize(this).

Basically these are the correct implementations of IDisposable according to the rule:

Sealed class

public sealed class Foo1 : IDisposable
{
    public void Dispose()
    {
        // Cleanup
    }
}

Simple implementation

public class Foo2 : IDisposable
{
    public void Dispose()
    {
        Dispose(true);
    }

    protected virtual void Dispose(bool disposing)
    {
        // Cleanup
    }
}

Implementation with a finalizer

public class Foo3 : IDisposable
{
    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    protected virtual void Dispose(bool disposing)
    {
        // Cleanup
    }

    ~Foo3()
    {
        Dispose(false);
    }
}

Should I implement IDisposable when class has IDisposable member but no unmanaged resources?

It looks like your case is indeed covered by some documentation, namely the design warning CA1001: Types that own disposable fields should be disposable.

That link has an example of what your IDisposable implementation should look like. It will be something like as follows. Eventual design guidelines can be found at CA1063: Implement IDisposable correctly.

  class FantasticFileService : IDisposable
  {
    private FileSystemWatcher fileWatch; // FileSystemWatcher is IDisposable

    public FantasticFileService(string watch)
    {
      fileWatch = new FileSystemWatcher(watch);
      fileWatch.Changed += OnFileChanged;
    }

    ~FantasticFileService()
    {
      Dispose(false);
    }

    protected virtual void Dispose(bool disposing)
    {
      if (disposing && fileWatch != null)
      {
        fileWatch.Dispose();
        fileWatch = null;
      }
    }

    public void Dispose()
    {
      Dispose(true);
      GC.SuppressFinalize(this);
    }
  }

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