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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef NSREFERENCEDELEMENT_H_
#define NSREFERENCEDELEMENT_H_
#include "mozilla/Attributes.h"
#include "mozilla/dom/Element.h"
#include "nsIAtom.h"
#include "nsIDocument.h"
#include "nsThreadUtils.h"
class nsIURI;
/**
* Class to track what element is referenced by a given ID.
*
* To use it, call Reset() to set it up to watch a given URI. Call get()
* anytime to determine the referenced element (which may be null if
* the element isn't found). When the element changes, ElementChanged
* will be called, so subclass this class if you want to receive that
* notification. ElementChanged runs at safe-for-script time, i.e. outside
* of the content update. Call Unlink() if you want to stop watching
* for changes (get() will then return null).
*
* By default this is a single-shot tracker --- i.e., when ElementChanged
* fires, we will automatically stop tracking. get() will continue to return
* the changed-to element.
* Override IsPersistent to return true if you want to keep tracking after
* the first change.
*/
class nsReferencedElement {
public:
typedef mozilla::dom::Element Element;
nsReferencedElement()
: mReferencingImage(false)
{}
~nsReferencedElement() {
Unlink();
}
/**
* Find which element, if any, is referenced.
*/
Element* get() { return mElement; }
/**
* Set up the reference. This can be called multiple times to
* change which reference is being tracked, but these changes
* do not trigger ElementChanged.
* @param aFrom the source element for context
* @param aURI the URI containing a hash-reference to the element
* @param aWatch if false, then we do not set up the notifications to track
* changes, so ElementChanged won't fire and get() will always return the same
* value, the current element for the ID.
* @param aReferenceImage whether the ID references image elements which are
* subject to the document's mozSetImageElement overriding mechanism.
*/
void Reset(nsIContent* aFrom, nsIURI* aURI, bool aWatch = true,
bool aReferenceImage = false);
/**
* A variation on Reset() to set up a reference that consists of the ID of
* an element in the same document as aFrom.
* @param aFrom the source element for context
* @param aID the ID of the element
* @param aWatch if false, then we do not set up the notifications to track
* changes, so ElementChanged won't fire and get() will always return the same
* value, the current element for the ID.
*/
void ResetWithID(nsIContent* aFrom, const nsString& aID,
bool aWatch = true);
/**
* Clears the reference. ElementChanged is not triggered. get() will return
* null.
*/
void Unlink();
void Traverse(nsCycleCollectionTraversalCallback* aCB);
protected:
/**
* Override this to be notified of element changes. Don't forget
* to call this superclass method to change mElement. This is called
* at script-runnable time.
*/
virtual void ElementChanged(Element* aFrom, Element* aTo) {
mElement = aTo;
}
/**
* Override this to convert from a single-shot notification to
* a persistent notification.
*/
virtual bool IsPersistent() { return false; }
/**
* Set ourselves up with our new document. Note that aDocument might be
* null. Either aWatch must be false or aRef must be empty.
*/
void HaveNewDocument(nsIDocument* aDocument, bool aWatch,
const nsString& aRef);
private:
static bool Observe(Element* aOldElement,
Element* aNewElement, void* aData);
class Notification : public nsISupports {
public:
virtual void SetTo(Element* aTo) = 0;
virtual void Clear() { mTarget = nullptr; }
virtual ~Notification() {}
protected:
explicit Notification(nsReferencedElement* aTarget)
: mTarget(aTarget)
{
NS_PRECONDITION(aTarget, "Must have a target");
}
nsReferencedElement* mTarget;
};
class ChangeNotification : public mozilla::Runnable,
public Notification
{
public:
ChangeNotification(nsReferencedElement* aTarget,
Element* aFrom, Element* aTo)
: Notification(aTarget), mFrom(aFrom), mTo(aTo)
{}
NS_DECL_ISUPPORTS_INHERITED
NS_IMETHOD Run() override {
if (mTarget) {
mTarget->mPendingNotification = nullptr;
mTarget->ElementChanged(mFrom, mTo);
}
return NS_OK;
}
virtual void SetTo(Element* aTo) override { mTo = aTo; }
virtual void Clear() override
{
Notification::Clear(); mFrom = nullptr; mTo = nullptr;
}
protected:
virtual ~ChangeNotification() {}
RefPtr<Element> mFrom;
RefPtr<Element> mTo;
};
friend class ChangeNotification;
class DocumentLoadNotification : public Notification,
public nsIObserver
{
public:
DocumentLoadNotification(nsReferencedElement* aTarget,
const nsString& aRef) :
Notification(aTarget)
{
if (!mTarget->IsPersistent()) {
mRef = aRef;
}
}
NS_DECL_ISUPPORTS
NS_DECL_NSIOBSERVER
private:
virtual ~DocumentLoadNotification() {}
virtual void SetTo(Element* aTo) override { }
nsString mRef;
};
friend class DocumentLoadNotification;
nsCOMPtr<nsIAtom> mWatchID;
nsCOMPtr<nsIDocument> mWatchDocument;
RefPtr<Element> mElement;
RefPtr<Notification> mPendingNotification;
bool mReferencingImage;
};
inline void
ImplCycleCollectionUnlink(nsReferencedElement& aField)
{
aField.Unlink();
}
inline void
ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
nsReferencedElement& aField,
const char* aName,
uint32_t aFlags = 0)
{
aField.Traverse(&aCallback);
}
#endif /*NSREFERENCEDELEMENT_H_*/
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