ios block循環參考問題

ios開發中，開了ARC模式，系統自動管理記憶體，如果程式中用到了block就要注意循環參考帶來的記憶體泄露問題了

這幾天遇到一個問題，正常頁面dismiss的時候是要調用dealloc方法的，但是我的程式就是不調用，研究了好久終於找到了問題出在哪裡了

起初的代碼如下：

- (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];

                                                                     }];

}

代碼錶面上看起來沒有什麼問題，但是細細研究就會發現兩個問題

1、block中引用到self，self 被block retain，sendedRequest又retain了該block的一根拷貝

2.sendedRequest是在self類中定義賦值，因此是被self retain

因此就形成了循環參考，不會調用dealloc

還有一個問題，只要重複性 timer 還沒有被 invalidated，target 對象就會被一直持有而不會被釋放。因此當你使用 self 當作 target 時，你就不能期望在 dealloc 中 invalidate timer，因為在 timer 沒有被invalidate 之前，dealloc 絕不會被調用。因此，需要找個合適的時機和地方來 invalidate timer，但絕不是在 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];

                                                                     }];

}

這樣就避免了循環參考，頁面登出時就會調用dealloc方法了