为什么Xcode Analyzer使用此代码给我一个内存泄漏警告？

Question

警告是:

存储在'escaped_value'中的对象的潜在泄漏

这是代码:

- (NSURL*)generateURL:(NSString*)baseURL params:(NSDictionary*)params {
    if (params) {
        NSMutableArray* pairs = [NSMutableArray array];
        for (NSString* key in params.keyEnumerator) {
            NSString* value = params[key];
            NSString* escaped_value = (__bridge NSString *)CFURLCreateStringByAddingPercentEscapes(
                                                                                          NULL, /* allocator */
                                                                                          (__bridge CFStringRef)value,
                                                                                          NULL, /* charactersToLeaveUnescaped */
                                                                                          (CFStringRef)@"!*'();:@&=+$,/?%#[]",
                                                                                          kCFStringEncodingUTF8);

            [pairs addObject:[NSString stringWithFormat:@"%@=%@", key, escaped_value]];
        }

        NSString* query = [pairs componentsJoinedByString:@"&"];
        NSString* url = [NSString stringWithFormat:@"%@?%@", baseURL, query];
        return [NSURL URLWithString:url];
    } else {
        return [NSURL URLWithString:baseURL];
    }
}

Answer 1

当您调用CFURLCreateStringByAddingPercentEscapes并且从不CFReleasing它时,您正在创建一个字符串.在对象超出范围之前CFRelease对象或将__bridge更改为__bridge_transfer以让ARC处理它.

__bridge_transfer告诉ARC,在演员阵容期间,对象的+1保留计数被转移到ARCs的责任范围内.ARC将根据其规则发布实例.

__bridge告诉ARC,在演员阵容期间没有转移保留计数.