Prevent crash when trying to close UIDocument - objective-c

Question

I am wondering how I can prevent a crash when trying to close UIDoc twice. I tried to make sure in my code that you (theoretically) can not close a UIDocument twice. However, it still happens sometimes and I don't know why. If it does, the app crashes:
2012-07-06 15:24:34.470 Meernotes[11620:707] ... doc state:Normal
2012-07-06 15:24:34.472 Meernotes[11620:707] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'closeWithCompletionHandler called while document is already closing'
*** First throw call stack:
(0x3720e88f 0x34f13259 0x3720e789 0x3720e7ab 0x312681d1 0xd19db 0x96f7f 0x9593f 0xacb8f 0x30f0cd23 0x37a7f933 0x371e2a33 0x371e2699 0x371e126f 0x371644a5 0x3716436d 0x33923439 0x30f10cd5 0x94fdd 0x94f78)
terminate called throwing an exception(lldb)
I tried to prevent the crash as follows, but it has no effect whatsoever (i.e. it will still crash):
-(void)closeDoc {
UIDocumentState state = _selectedDocument.documentState;
NSMutableArray * states = [NSMutableArray array];
if (state == 0) {
[states addObject:#"Normal"];
}
if (state & UIDocumentStateClosed) {
[states addObject:#"Closed"];
}
if (state & UIDocumentStateInConflict) {
[states addObject:#"In conflict"];
}
if (state & UIDocumentStateSavingError) {
[states addObject:#"Saving error"];
}
if (state & UIDocumentStateEditingDisabled) {
[states addObject:#"Editing disabled"];
}
NSLog(#"... doc state: %#", [states componentsJoinedByString:#", "]);
if (_selectedDocument.documentState & UIDocumentStateClosed) return;
[_selectedDocument closeWithCompletionHandler:^(BOOL success) {
NSLog(#"Closed document.");
// Check status
if (!success) {
NSLog(#"Failed to close %#", _selectedDocument.fileURL);
} else {
_selectedDocument = nil;
}
}];
}

Answer 1

It looks like UIDocument doesn't store the closing state, only normal and closed, so you'll have to do it yourself.
Add this to your class variables:
BOOL _documentClosing;
And add its use in your closeDoc method:
-(void)closeDoc {
if (_docClosing || (_selectedDocument.documentState & UIDocumentClosed) != 0)
return;
_docClosing = YES;
[_selectedDocument closeWithCompletionHandler:^(BOOL success) {
NSLog(#"Closed document.");
// Check status
if (!success) {
NSLog(#"Failed to close %#", _selectedDocument.fileURL);
} else {
_selectedDocument = nil;
_docClosing = NO;
}
}];
}

Answer 2

It's very important to know that each UIDocument object can only be opened and closed once. I had a lot of odd problems with UIDocuments before realizing this, both in the cloud and with local files. When you close a document set its pointer to nil, so you can't close it again. If you need to access the same file again later, create a new UIDocument with the same fileURL.
The error message you show above is one that appears when you try to re-use a document.