[Interest] [OS X] creating a QDialog from a WId?

[René J. V. Bertin]

Thiago Macieira wrote:


> This is a crash inside the Cocoa plugin. Unfortunately, I can't read Objective

It is indeed...

> C++ code, so I have absolutely no clue what this line does or how it can even
> crash:
> 
>     [m_contentView removeFromSuperview];

Supposing that is indeed the crashing function (my qcocoawindow.mm:1154 says 
[contentView retain]), then this is what it does:
https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ApplicationKit/Classes/NSView_Class/#//apple_ref/occ/instm/NSView/removeFromSuperview

but there are a few more or less self-evident ways this can go wrong:
- the (m_)contentView is not initialised, which means the removeFromSuperView 
message is sent to someplace it shouldn't go
- the instance was released already
- the method is called during display

and then there is the possibility that m_contentView or contentView correspond 
to a window that belongs to another application, because apparently a WId can be 
a simple cast of an NSView* :

WId QCocoaWindow::winId() const
{
    return WId(m_contentView);
}

It's not impossible that AppKit itself doesn't have any way of knowing whether 
an NSView is owned by the calling application or not because it's not designed 
to allow application to mess with each others' windows (other than through 
formal channels). In that case you'd have to keep track of all owned objects 
that can be exported as WIds, and do a lookup in each public function that 
accepts a WId. Sounds like a considerable overhead...

BTW, in principle it is possible with ObjC to send messages to (call methods of) 
objects that belong to another application. That does require some extra code 
however, and I cannot remember if each and every method can be used that way. 
I've never actually used this myself, but I have some doubts that you could just 
pass pointers to instances around and send them messages.

R.