通过引用访问实例变量是否安全? [英] Is accessing instance variables by reference safe?

问题描述

下面的两个代码段有什么区别?

What is the difference between the two code snippets below:

1.

__block __weak NSMutableArray *arrBlock = self.arr ;
[[AsyncRequest initRequest:url onCompletedBlock:^(NSMutableArray *arr) {
         arrBlock = arr;
    }]ExecuteRequest];

2.

id __weak weakself  = self;
[[AsyncRequest initRequest:url onCompletedBlock:^(NSMutableArray *arr) {
         weakself.arr = arr;
    }]ExecuteRequest];

它们都不引起保留周期，但是Apple

Neither of them cause retain cycles, but Apple suggests using the first one. Is there a problem with the second one?

推荐答案

它们有不同的效果.第一个更新本地变量，第二个更新实例变量(属性).

They have different effects. The first updates the local variable and the second updates the instance variable (property).

您要使用哪一个取决于您要发生的事情，但是我怀疑您想要第二个，因为如果该块是异步执行的，则第一个看起来像是无操作.

Which one you want to use depends on what you want to happen, however I suspect you want the second as the first looks like a no-op if that block is executed asynchronously.

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