Unusual crash with cocoa webView -elementAtPoint: (OS X) - objective-c

Question

I have a subclass of webView that overrides - hitTest: The basic idea is that I want clicks on the webView to pass through to the nextResponder if the click was on the body DOM element. The method looks like this
- (NSView *)hitTest:(NSPoint)aPoint
{
NSDictionary *dict = [self elementAtPoint:aPoint];
if([[dict valueForKey:#"WebElementDOMNode"] isKindOfClass:[DOMHTMLBodyElement class]])
{
return (NSView *)[self nextResponder];
}
return [super hitTest:aPoint];
}
When run, it crashes on elementAtPoint with EXC_BAD_ACCESS code=2
Now, it gets weirder. If I breakpoint the app at that line, and do a po [self elementAtPoint:aPoint] in LLDB, LLDB just hangs until I do a ^C.
Weirder yet. If I comment out everything but the last return, break on the return statement, and run po [self elementAtPoint:aPoint] in LLDB—I get exactly what I expect, a nice dictionary telling me all about the DOM at that point.
What could be causing this behavior?
Note: This is on OS X, not iOS.

Answer 1

What could be causing this behavior?
Just look at [WebView _elementAtWindowPoint:] and [WebView _frameViewAtWindowPoint:] implementations in the WebKit source code. Unfortunately, they use hitTest: to determine elementAtPoint:.
In my case, this workaround seems to work:
- (NSView *)hitTest:(NSPoint)point
{
if (m_hitTestEnabled)
{
[NSTimer scheduledTimerWithTimeInterval:0.
target:self
selector:#selector(hitTestDelayed:)
userInfo:#[ #(point.x), #(point.y) ]
repeats:NO];
}
return [super hitTest:point];
}
- (void)hitTestDelayed:(NSTimer *)timer
{
NSPoint point = NSMakePoint([[timer userInfo][0] floatValue], [[timer userInfo][1] floatValue]);
m_hitTestEnabled = false;
NSDictionary *dict = [self elementAtPoint:point];
m_hitTestEnabled = true;
if ([[dict valueForKey:#"WebElementDOMNode"] isKindOfClass:[DOMHTMLDivElement class]])
{
NSLog(#"divAtPoint: %#", dict);
}
}
m_hitTestEnabled is set to YES in the initWith... method.
Why with a timer? Such operations on WebView are allowed only in main thread. So, we cannot launch another thread to get elementAtPoint: and wait for its completion in the "main" hitTest:. Maybe someone will come up with a better solution.