WPF 源代码 资源字典 ResourceDictionary 设置 Source 属性的逻辑

        public Uri Source
        {
            get
            {
                return _source;
            }
            set
            {
                if (value == null || String.IsNullOrEmpty(value.OriginalString))
                {
                    throw new ArgumentException(SR.Get(SRID.ResourceDictionaryLoadFromFailure, value == null ? "''" : value.ToString()));
                }

                ResourceDictionaryDiagnostics.RemoveResourceDictionaryForUri(_source, this);

                ResourceDictionarySourceUriWrapper uriWrapper = value as ResourceDictionarySourceUriWrapper;

                Uri sourceUri;

                // If the Uri we received is a ResourceDictionarySourceUriWrapper it means
                // that it is being passed down by the Baml parsing code, and it is trying to give us more
                // information to avoid possible ambiguities in assembly resolving. Use the VersionedUri
                // to resolve, and the set _source to the OriginalUri so we don't change the return of Source property.
                // The versioned Uri is not stored, if the version info is needed while debugging, once this method
                // returns _reader should be set, from there BamlSchemaContext.LocalAssembly contains the version info.
                if (uriWrapper == null)
                {
                    _source = value;
                    sourceUri = _source;
                }
                else
                {
                    _source = uriWrapper.OriginalUri;
                    sourceUri = uriWrapper.VersionedUri;
                }

                Clear();


                Uri uri = BindUriHelper.GetResolvedUri(_baseUri, sourceUri);

                WebRequest request = WpfWebRequestHelper.CreateRequest(uri);
                WpfWebRequestHelper.ConfigCachePolicy(request, false);
                ContentType contentType = null;
                Stream s = null;

                try
                {
                     s = WpfWebRequestHelper.GetResponseStream(request, out contentType);
                }
                catch (System.IO.IOException)
                {
                     // 忽略细节处理的代码
                }

                // MimeObjectFactory.GetObjectAndCloseStream will try to find the object converter basing on the mime type.
                // It can be a sync/async converter. It's the converter's responsiblity to close the stream.
                // If it fails to find a convert, this call will return null.
                System.Windows.Markup.XamlReader asyncObjectConverter;
                ResourceDictionary loadedRD = MimeObjectFactory.GetObjectAndCloseStream(s, contentType, uri, false, false, false /*allowAsync*/, false /*isJournalNavigation*/, out asyncObjectConverter)
                                            as ResourceDictionary;

                if (loadedRD == null)
                {
                    throw new InvalidOperationException(SR.Get(SRID.ResourceDictionaryLoadFromFailure, _source.ToString()));
                }

                // ReferenceCopy all the key-value pairs in the _baseDictionary
                _baseDictionary = loadedRD._baseDictionary;

                // ReferenceCopy all the entries in the MergedDictionaries collection
                _mergedDictionaries = loadedRD._mergedDictionaries;

                // ReferenceCopy all of the deferred content state
                CopyDeferredContentFrom(loadedRD);

                // Take over the deferred resource references
                MoveDeferredResourceReferencesFrom(loadedRD);

                // Copy over the HasImplicitStyles flag
                HasImplicitStyles = loadedRD.HasImplicitStyles;

                // Copy over the HasImplicitDataTemplates flag
                HasImplicitDataTemplates = loadedRD.HasImplicitDataTemplates;

                // Copy over the InvalidatesImplicitDataTemplateResources flag
                InvalidatesImplicitDataTemplateResources = loadedRD.InvalidatesImplicitDataTemplateResources;

                // Set inheritance context on the copied values
                if (InheritanceContext != null)
                {
                    AddInheritanceContextToValues();
                }

                // Propagate parent owners to each of the acquired merged dictionaries
                if (_mergedDictionaries != null)
                {
                    for (int i = 0; i < _mergedDictionaries.Count; i++)
                    {
                        PropagateParentOwners(_mergedDictionaries[i]);
                    }
                }

                ResourceDictionaryDiagnostics.AddResourceDictionaryForUri(uri, this);

                if (!IsInitializePending)
                {
                    // Fire Invalidations for the changes made by asigning a new Source
                    NotifyOwners(new ResourcesChangeInfo(null, this));
                }
            }
        }

// 前置属性判断

// 清空当前资源字典的所有元素
Clear();

// 解析 Uri 获取资源
ResourceDictionary loadedRD = xx; // 这里的 loadedRD 就是 loadedR(esource)D(ictionary) 的意思

// 取出资源字典的值
_baseDictionary = loadedRD._baseDictionary;

// 取出资源字典加载的其他资源字典
_mergedDictionaries = loadedRD._mergedDictionaries;

// 其他杂项状态处理

     _source = value;
     sourceUri = _source;
     Uri uri = BindUriHelper.GetResolvedUri(_baseUri, sourceUri);

WebRequest request = WpfWebRequestHelper.CreateRequest(uri);
WpfWebRequestHelper.ConfigCachePolicy(request, false);
ContentType contentType = null;
Stream s = null;

try
{
    s = WpfWebRequestHelper.GetResponseStream(request, out contentType);
}
catch
{
  // 忽略细节代码
}

ResourceDictionary loadedRD = MimeObjectFactory.GetObjectAndCloseStream(s, contentType, uri, false, false, false /*allowAsync*/, false /*isJournalNavigation*/, out asyncObjectConverter) as ResourceDictionary;

                // ReferenceCopy all the key-value pairs in the _baseDictionary
                _baseDictionary = loadedRD._baseDictionary;

                // ReferenceCopy all the entries in the MergedDictionaries collection
                _mergedDictionaries = loadedRD._mergedDictionaries;

        private object GetValueWithoutLock(object key, out bool canCache)
        {
            object value = _baseDictionary[key];
            if (value != null)
            {
                OnGettingValuePrivate(key, ref value, out canCache);
            }
            else
            {
                canCache = true;

                //Search for the value in the Merged Dictionaries
                if (_mergedDictionaries != null)
                {
                    for (int i = MergedDictionaries.Count - 1; (i > -1); i--)
                    {
                        // Note that MergedDictionaries collection can also contain null values
                        ResourceDictionary mergedDictionary = MergedDictionaries[i];
                        if (mergedDictionary != null)
                        {
                            value = mergedDictionary.GetValue(key, out canCache);
                            if (value != null)
                            {
                                break;
                            }
                        }
                    }
                }
            }

            return value;
        }