Can't seem to cast from NSString* to CFString* using ARC
I am using the following code to obtain a file's file type in Objective-C (Mac OS X Cocoa Application):
NSString *kind = nil;
NSURL *url = [NSURL fileURLWithPath:[path stringByExpandingTildeInPath]];
LSCopyKindStringForURL((CFURLRef)url, (CFStringRef*)&kind);
return kind ? kind : @"";
However, the only error being produced is on the following line:
LSCopyKindStringForURL((CFURLRef)url, (CFStringRef*)&kind);
Saying:
C-style cast from 'NSString *__strong *' to 'CFStringRef *' (aka 'const __CFString **') casts away qualifiers
After doing some research, I saw that the __bridge keyword is required to make the cast from NSString* to CFStringRef* valid in ARC. So I stuck in the keyword, producing:
LSCopyKindStringForURL((CFURLRef)url, (__bridge CFStringRef*)&kind);
Now, I am receiving the following error:
Incompatible types casting 'NSString *__strong *' to 'CFStringRef *' (aka 'const __CFString **') with a __bridge cast
It's starting to drive me crazy... no matter what I seem to try, I just can't make the error go away. Any ideas?
There's a simple workaround. Use an actual CFStringRef variable and cast it when it comes time to return it as an NSString :
NSURL *url = [NSURL fileURLWithPath:[path stringByExpandingTildeInPath]];
CFStringRef kind;
LSCopyKindStringForURL((CFURLRef)url, &kind);
return kind ? CFBridgingRelease(kind) : @"";
我使用以下来获得善意
(NSURL *)path
NSString *tempKind;
[path getResourceValue:&tempKind forKey:NSURLLocalizedTypeDescriptionKey error:nil];
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