iOS 获取字符串的首字母, 缺省为#

- (NSString*)firstChar:(NSString *)string {
    if ((string == nil)|| (string == NULL) || ([[string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] length] == 0) || [string isKindOfClass:[NSNull class]]) {
        return @"#";
    }
    
    NSMutableString *source = [NSMutableString stringWithString:string];
    CFStringTransform((CFMutableStringRef)source, NULL, kCFStringTransformMandarinLatin, NO);
    CFStringTransform((CFMutableStringRef)source, NULL, kCFStringTransformStripDiacritics, NO);
    
    return [[source capitalizedString] substringToIndex:1];
}