Hello, I added <https://bugzilla.mozilla.org/show_bug.cgi?id=1455514>
some static `FromEventTarget` helper methods like `FromNode`. This
allows you to avoid to QI from `EventTarget` pointers.
For example, when you need to get `Element` pointer from `EventTarget`
pointer, previous you needed to do:
namespace mozilla::dom {
void Foo(EventTarget* aEventTarget) {
nsCOMPtr<Element> element = do_QueryInterface(aEventTarget);
if (!element) {
return;
}
...
}
} // namespace mozilla::dom
Now, you can write this as:
namespace mozilla::dom {
void Foo(EventTarget* aEventTarget) {
Element* element = Element::FromEventTargetOrNull(aEventTarget);
if (!element) {
return;
}
...
}
} // namespace mozilla::dom
`nsINode::FromEventTarget()`, `nsPIDOMWindowInner::FromEventTarget()`,
`nsPIDOMWindowOuter::FromEventTarget()` and
`nsPIWindowRoot::FromEventTarget()` resolve this with *one**virtual
call* so that they are never slower than `do_QueryInterface`.
Subclasses of `nsINode` helpers (e.g., `nsIContent::FromEventTarget()`,
`Element::FromEventTarget()`, etc) resolve this with *two****virtual
calls*. I guess that this is faster than `do_QueryInterface` in most
cases since IID comparison is not cheap and most concrete classes of
`nsINode` have a lot of interfaces.
`FromEventTarget` and `FromEventTargetOrNull` helpers for subclasses of
`nsINode` are declared and defined by `NS_IMPL_FROMNODE_HELPER` macro
<https://searchfox.org/mozilla-central/rev/364aa1d41eb9b5ea583fa6cedc56fb5343e3514f/dom/base/nsINode.h#2280,2290-2308,2310,2326-2338>
automatically. So all classes which have `FromNode` and `FromNodeOrNull`
have the new helper methods too.
Finally, like `dom::Element` and `dom::Text`, there are similar utility
methods in `dom::EventTarget`
<https://searchfox.org/mozilla-central/rev/364aa1d41eb9b5ea583fa6cedc56fb5343e3514f/dom/events/EventTarget.h#128-148>
now.
--
Masayuki Nakano<[email protected]>
Working on DOM, Events, editor and IME handling for Gecko
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