在我们使用操作系统，系统通常可以根据文件扩展名/后缀，来判断文件类型，并显示相应图标。那么，iOS 中可以怎样实现呢？
iOS 可以通过 UTI 来进行转换。UTI 是什么呢，用过 Media 相关的框架的同学可能不会陌生。需要了解的同学，可浏览以下资料： - Uniform Type Identifier Concepts - Uniform Type Identifier
具体实现代码如下：
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NSString *UTIForExtension(NSString *extension) {
NSString *theUTI = (__bridge_transfer NSString *)UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, (__bridge CFStringRef)(extension), NULL);
return theUTI;
}
BOOL extensionConformToUTI(NSString *extension, CFStringRef theUTI) {
NSString *preferredUTI = UTIForExtension(extension);
return (UTTypeConformsTo((__bridge CFStringRef) preferredUTI, theUTI));
}
BOOL extensionLikelyImage(NSString *extension) {
return extensionConformToUTI(extension, CFSTR("public.image"));
}
BOOL extensionLikelyAudio(NSString *extension) {
return extensionConformToUTI(extension, CFSTR("public.audio"));
}
BOOL extensionLikelyMovie(NSString *extension) {
return extensionConformToUTI(extension, CFSTR("public.movie"));
}
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🎁彩蛋
顺便的，给出 UTI 与 mimeType 的转换，以及相关的实用函数。
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NSString *mimeTypeForUTI(NSString *aUTI) {
CFStringRef theUTI = (__bridge CFStringRef) aUTI;
CFStringRef mimeType = UTTypeCopyPreferredTagWithClass(theUTI, kUTTagClassMIMEType);
return (__bridge_transfer NSString *)mimeType;
}
NSArray *uniqueArray(NSArray *anArray) {
NSMutableArray *copiedArray = [NSMutableArray arrayWithArray:anArray];
for (id object in anArray) {
[copiedArray removeObjectIdenticalTo:object];
[copiedArray addObject:object];
}
return copiedArray;
}
NSArray *conformanceArray(NSString *aUTI) {
NSMutableArray *results = [NSMutableArray arrayWithObject:aUTI];
NSDictionary *dictionary = utiDictionary(aUTI);
id conforms = dictionary[(__bridge NSString *)kUTTypeConformsToKey];
if (!conforms) return results;
if ([conforms isKindOfClass:[NSString class]]) {
[results addObjectsFromArray:conformanceArray(conforms)];
return uniqueArray(results);
}
if ([conforms isKindOfClass:[NSArray class]]) {
for (NSString *eachUTI in (NSArray *) conforms)
[results addObjectsFromArray:conformanceArray(eachUTI)];
return uniqueArray(results);
}
return results;
}
NSArray *allExtensions(NSString *aUTI) {
NSMutableArray *results = [NSMutableArray array];
NSArray *conformance = conformanceArray(aUTI);
for (NSString *eachUTI in conformance) {
NSDictionary *dictionary = utiDictionary(eachUTI);
NSDictionary *extensions = dictionary[(__bridge NSString *)kUTTypeTagSpecificationKey];
id fileTypes = extensions[(__bridge NSString *)kUTTagClassFilenameExtension];
if ([fileTypes isKindOfClass:[NSArray class]])
[results addObjectsFromArray:(NSArray *) fileTypes];
else if ([fileTypes isKindOfClass:[NSString class]])
[results addObject:(NSString *) fileTypes];
}
return uniqueArray(results);
}
NSArray *allMIMETypes(NSString *aUTI) {
NSMutableArray *results = [NSMutableArray array];
NSArray *conformance = conformanceArray(aUTI);
for (NSString *eachUTI in conformance) {
NSDictionary *dictionary = utiDictionary(eachUTI);
NSDictionary *extensions = dictionary[(__bridge NSString *)kUTTypeTagSpecificationKey];
id fileTypes = extensions[(__bridge NSString *)kUTTagClassMIMEType];
if ([fileTypes isKindOfClass:[NSArray class]])
[results addObjectsFromArray:(NSArray *) fileTypes];
else if ([fileTypes isKindOfClass:[NSString class]])
[results addObject:(NSString *) fileTypes];
}
return uniqueArray(results);
}
NSDictionary *utiDictionary(NSString *aUTI) {
NSDictionary *dictionary = (__bridge_transfer NSDictionary *)UTTypeCopyDeclaration((__bridge CFStringRef) aUTI);
return dictionary;
}
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