private static IApplication CreateInstance()
{
var handler = QueryType;
if (handler == null)
{
throw new InvalidOperationException(
"Cannot create an instance because the QueryType event " +
"handler was never set.");
}
var args = new QueryTypeEventArgs();
handler.Invoke(null, args);
if (args.Type == null)
{
throw new InvalidOperationException(
"Cannot create an instance because the type has not been " +
"provided.");
}
// NOTE: here's where things get weird. you need to define your own
// sort of "contract" for what type of constructor you will allow.
// you might not even use a constructor here... but you need to
// define what mechanism the provided type must have to provide
// you with a singleton instance. i'm a fan of providing a type
// with a private parameterless constructor, so i'll demonstrate
// with that. your requirements will change what this section of
// code looks like.
if (!typeof(IApplication).IsAssignableFrom(args.Type))
{
throw new InvalidOperationException(
"Cannot create an instance because the provided type does " +
"not implement the IApplication interface.");
}
const BindingFlags FLAGS =
BindingFlags.CreateInstance |
BindingFlags.Instance |
BindingFlags.NonPublic;
var constructors = args.Type.GetConstructors(FLAGS);
if (constructors.Length != 1)
{
throw new InvalidOperationException(
"Cannot create an instance because a single private " +
"parameterless constructor was expected.");
}
return((IApplication)constructors[0].Invoke(null));
}
private static IApplication CreateInstance()
{
var handler = QueryType;
if (handler == null)
{
throw new InvalidOperationException(
"Cannot create an instance because the QueryType event " +
"handler was never set.");
}
var args = new QueryTypeEventArgs();
handler.Invoke(null, args);
if (args.Type == null)
{
throw new InvalidOperationException(
"Cannot create an instance because the type has not been " +
"provided.");
}
// NOTE: here's where things get weird. you need to define your own
// sort of "contract" for what type of constructor you will allow.
// you might not even use a constructor here... but you need to
// define what mechanism the provided type must have to provide
// you with a singleton instance. i'm a fan of providing a type
// with a private parameterless constructor, so i'll demonstrate
// with that. your requirements will change what this section of
// code looks like.
if (!typeof(IApplication).IsAssignableFrom(args.Type))
{
throw new InvalidOperationException(
"Cannot create an instance because the provided type does " +
"not implement the IApplication interface.");
}
const BindingFlags FLAGS =
BindingFlags.CreateInstance |
BindingFlags.Instance |
BindingFlags.NonPublic;
var constructors = args.Type.GetConstructors(FLAGS);
if (constructors.Length != 1)
{
throw new InvalidOperationException(
"Cannot create an instance because a single private " +
"parameterless constructor was expected.");
}
return (IApplication)constructors[0].Invoke(null);
}