/// <summary>
/// This is a helper method that returns the target object for a delegate.
/// If the delegate was created to proxy a generic delegate, this will correctly
/// return the original object, not the proxy.
/// </summary>
/// <param name="callback">The delegate to get the target for.</param>
/// <returns>The object that is the callback target. This can return null if the callback represents a static object.</returns>
/// <exception cref="ArgumentNullException">If callback is null.</exception>
protected static object GetTarget(Delegate callback)
{
if (callback == null)
{
throw FxTrace.Exception.ArgumentNull("callback");
}
ICallbackProxy proxy = callback.Target as ICallbackProxy;
if (proxy != null)
{
return(proxy.OriginalTarget);
}
return(callback.Target);
}
/// <summary>
/// This is a helper method that performs a Delegate.Remove, but knows
/// how to unwrap delegates that are proxies to generic callbacks. Use
/// this in your Unsubscribe implementations.
/// </summary>
/// <param name="existing">The existing delegate to remove the callback from.</param>
/// <param name="toRemove">The callback to remove.</param>
/// <returns>A new value to assign to the existing delegate.</returns>
protected static Delegate RemoveCallback(Delegate existing, Delegate toRemove)
{
if (existing == null)
{
return(null);
}
if (toRemove == null)
{
return(existing);
}
ICallbackProxy toRemoveProxy = toRemove.Target as ICallbackProxy;
if (toRemoveProxy == null)
{
// The item to be removed is a normal delegate. Just call
// Delegate.Remove
return(Delegate.Remove(existing, toRemove));
}
toRemove = toRemoveProxy.OriginalDelegate;
Delegate[] invocationList = existing.GetInvocationList();
bool removedItems = false;
for (int idx = 0; idx < invocationList.Length; idx++)
{
Delegate item = invocationList[idx];
ICallbackProxy itemProxy = item.Target as ICallbackProxy;
if (itemProxy != null)
{
item = itemProxy.OriginalDelegate;
}
if (item.Equals(toRemove))
{
invocationList[idx] = null;
removedItems = true;
}
}
if (removedItems)
{
// We must create a new delegate containing the
// invocation list that is is left
existing = null;
foreach (Delegate d in invocationList)
{
if (d != null)
{
if (existing == null)
{
existing = d;
}
else
{
existing = Delegate.Combine(existing, d);
}
}
}
}
return(existing);
}
