[Mono-osx] Problem canceling the opening of a NSDocument

[Dan Fry]

Hello Jon,

I had a similar problem with a different method (ReadFromUrl) where 
Cocoa was supplying NULL for the outError parameter in some cases, and 
it's not possible to convert null to an "out NSError" parameter in C#.

In the end I just didn't use the method from MonoMac and defined my own 
like this:

[Export("readFromURL:ofType:error:")]
private bool ReadFromUrl2(NSUrl absoluteUrl, string typeName, IntPtr pOutError)
{
     // Set this to an NSError object if an error occurs
     NSError nsError;

     // ...

     // Write the error to the out parameter
     if (pOutError != IntPtr.Zero)
     {
         if (nsError == null)
         {
             Marshal.WriteIntPtr(pOutError, IntPtr.Zero);
         }
         else
         {
             Marshal.WriteIntPtr(pOutError, nsError.Handle);
         }
     }
}


Maybe not the best way of solving it, but it worked for me!

Dan

On 25/04/2012 05:03, Jon Lipsky wrote:
> Hi All,
>
> I'm running into a strange problem that I though perhaps someone else 
> might have run into and might have a solution for.
>
> If I were writing a document based application in Objective-C and 
> wanted to the user to be able to cancel the opening of a document, I 
> could do something like this (which I can confirm works fine):
>
> - (BOOL)readFromData:(NSData *)data ofType:(NSString *)typeName 
> error:(NSError **)outError
> {
>     // Loading code here...
>
>     *outError = [NSErrorerrorWithDomain:NSCocoaErrorDomain 
> code:NSUserCancelledError userInfo:nil];
> returnNO;
> }
>
> The (what seems to me) obvious thing to do in MonoMac would be to 
> implement this:
>
> public override bool ReadFromData (NSData data, string typeName, out 
> NSError outError)
> {
> // Loading code here...
>
> outError = NSError.FromDomain(NSError.CocoaErrorDomain,1376);
> return false;
> }
>
>
> However, when I do so, my app crashes with the following stack trace:
>
>
> #0  0x9287dfd5 in __wait4 ()
> #1  0x93be04ec in waitpid$UNIX2003 ()
> #2  0x0009fe9b in mono_handle_native_sigsegv (signal=11, 
> ctx=0xbfffea5c) at mini-exceptions.c:2192
> #3  0x00004f6e in mono_sigsegv_signal_handler (_dummy=10, 
> info=0xbfffea1c, context=0xbfffea5c) at mini.c:5917
> #4 <signal handler called>
> #5  0x9249cd44 in objc_msgSend ()
> #6  0x991622cc in -[NSDocumentController(NSInternal) 
> _fixedFailureReasonFromError:] ()
> #7  0x9916b5f4 in -[NSDocumentController 
> _willPresentOpeningError:forURL:] ()
> #8  0x9916b197 in -[NSDocumentController 
> _openDocumentsWithContentsOfURLs:presentErrors:completionHandler:] ()
> #9  0x9915f749 in -[NSDocumentController openDocument:] ()
> (Rest of stack trace omitted)
>
> Has anyone else run into this problem, and if so were you able to find 
> a solution/workaround?
>
> Thanks,
> Jon...
>
>
> _______________________________________________
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> Mono-osx at lists.ximian.com
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