iOS 给参数用ascll排序

/** 对字典(Key-Value)排序
 @param dict 要排序的字典
 */
+ (NSMutableDictionary *)sortedDictionary:(NSMutableDictionary *)dict {
    NSMutableString *contentString =[NSMutableString string];
    NSArray *keys = [dict allKeys];
    //排序
    NSArray *sortedArray = [keys sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        return [obj1 compare:obj2];
    }];
    //拼接 把排序后的字典拼接成string
    for (NSString *keyStr in sortedArray) {
        if (![[dict objectForKey:keyStr] isEqualToString:@""] && ![[dict objectForKey:keyStr] isEqualToString:@"key"] ) {
            [contentString appendFormat:@"%@=%@&", keyStr, [dict objectForKey:keyStr]];
        }
    }
    contentString = (NSMutableString *)[contentString substringToIndex:contentString.length-1];
    NSLog(@"%@", contentString);
    
    //加密 把拼接后的参数加密生产sign
    NSString *signStr = [[NSString stringWithFormat:@"%@%@", contentString, MX_KEY] MD5];
    [dict setObject:signStr forKey:@"sign"];
    
    return dict;
}