// retrieve the value, using the cache if necessary
internal object GetValue(object item, PropertyDescriptor pd, bool indexerIsNext)
{
if (!ShouldCache(item, pd))
{
// normal case - just get the value the old-fashioned way
return(pd.GetValue(item));
}
else
{
// lazy creation of the cache
if (_table == null)
{
_table = new HybridDictionary();
}
// look up the value in the cache
bool isXLinqCollectionProperty = SystemXmlLinqHelper.IsXLinqCollectionProperty(pd);
ValueTableKey key = new ValueTableKey(item, pd);
object value = _table[key];
Action FetchAndCacheValue = () =>
{
// if there's no entry, fetch the value and cache it
if (value == null)
{
if (SystemDataHelper.IsDataSetCollectionProperty(pd))
{
// intercept GetValue calls for certain ADO properties
value = SystemDataHelper.GetValue(item, pd, !FrameworkAppContextSwitches.DoNotUseFollowParentWhenBindingToADODataRelation);
}
else if (isXLinqCollectionProperty)
{
// interpose our own value for special XLinq properties
value = new XDeferredAxisSource(item, pd);
}
else
{
value = pd.GetValue(item);
}
if (value == null)
{
value = CachedNull; // distinguish a null value from no entry
}
// for DataSet properties, store a weak reference to avoid
// a memory leak
if (SystemDataHelper.IsDataSetCollectionProperty(pd))
{
value = new WeakReference(value);
}
_table[key] = value;
}
if (SystemDataHelper.IsDataSetCollectionProperty(pd))
{
// we stored a weak reference - decode it now
WeakReference wr = value as WeakReference;
if (wr != null)
{
value = wr.Target;
}
}
};
FetchAndCacheValue();
if (value == null)
{
// we can only get here if we cached a weak reference
// whose target has since been GC'd. Repeating the call
// will refetch the value from the item, and is guaranteed
// to set value to non-null.
FetchAndCacheValue();
}
// decode null, if necessary
if (value == CachedNull)
{
value = null;
}
else if (isXLinqCollectionProperty && !indexerIsNext)
{
// The XLinq properties need special help. When the path
// contains "Elements[Foo]", we should return the interposed
// XDeferredAxisSource; the path worker will then call the XDAS's
// indexer with argument "Foo", and obtain the desired
// ObservableCollection. But when the path contains "Elements"
// with no indexer, we should return an ObservableCollection
// corresponding to the full set of children.
// [All this applies to "Descendants" as well.]
XDeferredAxisSource xdas = (XDeferredAxisSource)value;
value = xdas.FullCollection;
}
return(value);
}
}