Check whether a character is renderable on iOS

renderability.m

/* The character we are going to check*/
NSString *character = @"字";

/* Turn it into a character set ahead of our comparison */
NSCharacterSet *characterSet = [NSCharacterSet characterSetWithCharactersInString:character];

/* Fetch the system fallback font, as [UIFont familyNames] won't include it */
UIFontDescriptor *fallbackFontDescriptor = [UIFont fontWithName:@".PhoneFallBack" size:12.0f].fontDescriptor;

/* Start with the fallback font's character set */
NSMutableCharacterSet *renderableCharacterSet = [[fallbackFontDescriptor objectForKey:UIFontDescriptorCharacterSetAttribute] mutableCopy];
        
/* Create a union of all character sets. You'll want to cache this as it's too slow to be called every time you do this */
for (NSString *familyName in [UIFont familyNames]) {
    for (NSString *fontName in [UIFont fontNamesForFamilyName:familyName]) {
        UIFontDescriptor *fontDescriptor = [UIFont fontWithName:fontName size:12.0f].fontDescriptor;
        [renderableCharacterSet formUnionWithCharacterSet:[fontDescriptor objectForKey:UIFontDescriptorCharacterSetAttribute]];
    }
}

/* Finally, make the comparison */
NSLog(@"%@", [renderableCharacterSet isSupersetOfSet:characterSet] ? @"character is renderable" : @"character is not renderable");