ios block循环引用问题

ios开发中，开了arc模式，自动管理内存，如果程序中用到了block就要注意循环引用带来的内存泄露问题了

这几天遇到一个问题，正常页面dismiss的时候是要调用dealloc方法的，但是我的程序就是不调用，研究了好久终于找到了问题出在哪里了

起初的代码如下：

- (void)getmyrelatedshops

{

    [self.loadtimer invalidate];

    self.loadtimer = [nstimer scheduledtimerwithtimeinterval:0.1

                                                 target:discoverview

                                               selector:@selector(loadwaiting)

                                               userinfo:nil

                                                repeats:yes];

    

    sendedrequest = [[findshopservice sharedinstance] getmyrelatedshopswithpageno:pageno

                                                                     successblock:^(tmrequest *request){

                                                                         [self.loadtimer invalidate];

                                                                         [self shoplistrequestfinished:request];

                                                                     }failedblock:^(tmrequest *failedrequest){

                                                                         [self.loadtimer invalidate];

                                                                         [self shoplistrequestfailed:failedrequest];

                                                                     }];

}

代码表面上看起来没有什么问题，但是细细研究就会发现两个问题

1、block中引用到self，self 被block retain，sendedrequest又retain了该block的一根拷贝

2.sendedrequest是在self类中定义赋值，因此是被self retain

因此就形成了循环引用，不会调用dealloc

还有一个问题，只要重复性 timer 还没有被 invalidated，target 对象就会被一直持有而不会被释放。因此当你使用 self 当作 target 时，你就不能期望在 dealloc 中 invalidate timer，因为在 timer 没有被invalidate 之前，dealloc 绝不会被调用。因此，需要找个合适的时机和地方来 invalidate timer，但绝不是在 dealloc 中。

修改如下

- (void)getmyrelatedshops

{

    [self.loadtimer invalidate];

    self.loadtimer = [nstimer scheduledtimerwithtimeinterval:0.1

                                                 target:discoverview

                                               selector:@selector(loadwaiting)

                                               userinfo:nil

                                                repeats:yes];

   

    __unsafe_unretained findshopvc *wfindshopvc = self;

   

    sendedrequest = [[findshopservice sharedinstance] getmyrelatedshopswithpageno:pageno

                                                                     successblock:^(tmrequest *request){

                                                                         [wfindshopvc.loadtimer invalidate];

                                                                         [wfindshopvc shoplistrequestfinished:request];

                                                                     }failedblock:^(tmrequest *failedrequest){

                                                                         [wfindshopvc.loadtimer invalidate];

                                                                         [wfindshopvc shoplistrequestfailed:failedrequest];

                                                                     }];

}

这样就避免了循环引用，页面注销时就会调用dealloc方法了