Capturing self strongly in this block is likely to lead to a retain cycle

在block里引用self，xcode给出了这个warning：

Capturing self strongly in this block is likely to lead to a retain cycle

在SO上搜索了一番，好像和我的场景不太一样。最后我解决的办法是：

__block AddShopViewController *weakSelf = self;

然后在block里调用weakSelf：

[weakSelf clearFormAfterAppend];