Releasing temporary COM objects
My biggest gripe would be the name, T
; Add
might be more illusrative of the usage. I'd also add where T : class
to the generic method, but the "fluent API" seems usable. I'd also be inclined to flatten the code a bit. I can also see some ways of using the Expression
API to walk an entire tree and capture all the intermediate steps, but it wouldn't be trivial - but imagine:
using(var com = new SomeWrapper()) {
var baz = com.Add(() => new MyComObject().Foo.Bar.Baz);
}
where that is an expression tree and we get the intermediaries automatically.
(also, you could Clear()
or null
the list in Dispose()
)
Like so:
static class ComExample {
static void Main()
{
using (var wrapper = new ReleaseWrapper())
{
var baz = wrapper.Add(
() => new Foo().Bar.Baz);
Console.WriteLine(baz.Name);
}
}
}
class ReleaseWrapper : IDisposable
{
List<object> objects = new List<object>();
public T Add<T>(Expression<Func<T>> func)
{
return (T)Walk(func.Body);
}
object Walk(Expression expr)
{
object obj = WalkImpl(expr);
if (obj != null && Marshal.IsComObject(obj) && !objects.Contains(obj))
{
objects.Add(obj);
}
return obj;
}
object[] Walk(IEnumerable<Expression> args)
{
if (args == null) return null;
return args.Select(arg => Walk(arg)).ToArray();
}
object WalkImpl(Expression expr)
{
switch (expr.NodeType)
{
case ExpressionType.Constant:
return ((ConstantExpression)expr).Value;
case ExpressionType.New:
NewExpression ne = (NewExpression)expr;
return ne.Constructor.Invoke(Walk(ne.Arguments));
case ExpressionType.MemberAccess:
MemberExpression me = (MemberExpression)expr;
object target = Walk(me.Expression);
switch (me.Member.MemberType)
{
case MemberTypes.Field:
return ((FieldInfo)me.Member).GetValue(target);
case MemberTypes.Property:
return ((PropertyInfo)me.Member).GetValue(target, null);
default:
throw new NotSupportedException();
}
case ExpressionType.Call:
MethodCallExpression mce = (MethodCallExpression)expr;
return mce.Method.Invoke(Walk(mce.Object), Walk(mce.Arguments));
default:
throw new NotSupportedException();
}
}
public void Dispose()
{
foreach(object obj in objects) {
Marshal.ReleaseComObject(obj);
Debug.WriteLine("Released: " + obj);
}
objects.Clear();
}
}