ios - swift使用闭包传值

Question

1.我有一个swift项目，在XMPP注册模块，我使用闭包传值（代理会了，学学闭包用法），把注册结果传回控制器。
1 初始化

2注册成功赋值

3 作为返回值

4 在控制器中调用

5 结果是不注册他直接不注册，也不连接服务器了。直接返回

6 然后 我找到一个解决办法，一开始给上一种注册结果

7 再 返回

8 最后 结果出来了 注册成功
但是 把我给他初始化赋的结果也打印出来了

咋回事啊 ？

Answer 1

I see that this of yours has nothing to do with closure Closure

Closure 并没有关系

以下解答
此次 Crash 的问题很明显, 你对一个值为 nil 的 Optional 类型进行了强制解包

图5：'fatal error: unexpectedly found nil while unwrapping an optional value'

原因

1. 你的 connectToHost() 应该是异步方法. 该行执行后, 立即就执行了 return registerRes!

2. 但此时, 你的连接还进行中还未回调 func xmppStreamDidRegister(sender: XMPPStream!) 方法

3. 你的 registerRes 还是初始化的时候的值 nilThe following answer
   The problem with this crash is obvious, you forced a Optional type with a value of nil Unpack

   🎜Figure 5: 'fatal error: unexpectedly found nil while unwrapping an optional value'

   🎜Reason
   1. 🎜Your connectToHost() should be an asynchronous method. After this line is executed, return registerRes!

   is executed immediately
   2. 🎜But at this time, your connection is still in progress and the func xmppStreamDidRegister(sender: XMPPStream!) method has not been called back yet

   3. 🎜Your registerRes is still the value nil when initialized

Answer 2

Your whole process has nothing to do with closures... Since your variable will definitely have a value, you can actually use an exclamation mark instead of a question mark, so you don't need to assign nil to it when creating it, and you don't need to manually unpack it when getting it. Well, I'm just talking about a small problem in your code. As for the reason for the question you want to ask, it has been mentioned above. You can create a callback and hang this callback on connectHost. It's just that this will open a hole in each layer to pass the callback... Of course, there are elegant solutions. There is a project on Github called Async that you can refer to, because I haven't looked at its implementation carefully and it's hard to show off here.