layout/style/MediaQueryList.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* implements DOM interface for querying and observing media queries */
   8
   9 #ifndef mozilla_dom_MediaQueryList_h
  10 #define mozilla_dom_MediaQueryList_h
  11
  12 #include "nsISupports.h"
  13 #include "nsCycleCollectionParticipant.h"
  14 #include "nsCOMPtr.h"
  15 #include "nsTArray.h"
  16 #include "mozilla/LinkedList.h"
  17 #include "mozilla/Attributes.h"
  18 #include "nsWrapperCache.h"
  19 #include "mozilla/DOMEventTargetHelper.h"
  20 #include "mozilla/dom/MediaQueryListBinding.h"
  21
  22 namespace mozilla::dom {
  23
  24 class MediaList;
  25
  26 class MediaQueryList final : public DOMEventTargetHelper,
  27                              public LinkedListElement<MediaQueryList> {
  28  public:
  29   // The caller who constructs is responsible for calling Evaluate
  30   // before calling any other methods.
  31   MediaQueryList(Document* aDocument, const nsACString& aMediaQueryList,
  32                  CallerType);
  33
  34  private:
  35   ~MediaQueryList();
  36
  37  public:
  38   NS_DECL_ISUPPORTS_INHERITED
  39   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(MediaQueryList, DOMEventTargetHelper)
  40
  41   nsISupports* GetParentObject() const;
  42
  43   void MediaFeatureValuesChanged();
  44
  45   // Returns whether we need to notify of the change by dispatching a change
  46   // event.
  47   [[nodiscard]] bool EvaluateOnRenderingUpdate();
  48   void FireChangeEvent();
  49
  50   JSObject* WrapObject(JSContext* aCx,
  51                        JS::Handle<JSObject*> aGivenProto) override;
  52
  53   // WebIDL methods
  54   void GetMedia(nsACString& aMedia) const;
  55   bool Matches();
  56   void AddListener(EventListener* aListener, ErrorResult& aRv);
  57   void RemoveListener(EventListener* aListener, ErrorResult& aRv);
  58
  59   IMPL_EVENT_HANDLER(change)
  60
  61   bool HasListeners() const;
  62
  63   void Disconnect();
  64
  65   size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const;
  66
  67  private:
  68   void LastRelease() final {
  69     auto* listElement = static_cast<LinkedListElement<MediaQueryList>*>(this);
  70     if (listElement->isInList()) {
  71       listElement->remove();
  72     }
  73   }
  74
  75   void RecomputeMatches();
  76
  77   // We only need a pointer to the document to support lazy
  78   // reevaluation following dynamic changes.  However, this lazy
  79   // reevaluation is perhaps somewhat important, since some usage
  80   // patterns may involve the creation of large numbers of
  81   // MediaQueryList objects which almost immediately become garbage
  82   // (after a single call to the .matches getter).
  83   //
  84   // This pointer does make us a little more dependent on cycle
  85   // collection.
  86   //
  87   // We have a non-null mDocument for our entire lifetime except
  88   // after cycle collection unlinking.  Having a non-null mDocument
  89   // is equivalent to being in that document's mDOMMediaQueryLists
  90   // linked list.
  91   RefPtr<Document> mDocument;
  92   const RefPtr<const MediaList> mMediaList;
  93   // Whether our MediaList depends on our viewport size. Our medialist is
  94   // immutable, so we can just compute this once and carry on with our lives.
  95   const bool mViewportDependent : 1;
  96   // The matches state.
  97   // https://drafts.csswg.org/cssom-view/#mediaquerylist-matches-state
  98   bool mMatches : 1;
  99   // The value of the matches state on creation, or on the last rendering
 100   // update, in order to implement:
 101   // https://drafts.csswg.org/cssom-view/#evaluate-media-queries-and-report-changes
 102   bool mMatchesOnRenderingUpdate : 1;
 103 };
 104
 105 }  // namespace mozilla::dom
 106
 107 #endif /* !defined(mozilla_dom_MediaQueryList_h) */