ios tips

1. 代码块：
   精简代码, 返回最后一句的值，这个方法有一个优点，所有的变量都在代码块中，也就是只在代码块的区域中有效，这意味着可以减少对其他作用域的命名污染。

NSURL *url = ({ NSString *urlString = [NSString stringWithFormat:@"%@/%@", baseURLString, endpoint]; 
[NSURL URLWithString:urlString];
});

2. 关于编译器：

• 关闭警告：

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
[myObj performSelector:mySelector withObject:name];
#pragma clang diagnostic pop

• 忽略没用的变量
  #pragma unused (foo)
• 明确定义错误和警告

#error Whoa, buddy, you need to check for zero here!
#warning Dude, don't compare floating point numbers like this!

3. block
   下面的方法可以避免循环引用，但是执行多行时，可能变成Nil;

__weak typeof(self) weakSelf = self;
dispatch_block_t block = ^{ [weakSelf doSomething]; // weakSelf != nil 
// preemption, weakSelf turned nil
 [weakSelf doSomethingElse]; // weakSelf == nil
};

最好这样调用：

__weak typeof(self) weakSelf = self;
myObj.myBlock = ^{ 
__strong typeof(self) strongSelf = weakSelf; 
if (strongSelf) { [strongSelf doSomething]; // strongSelf != nil 
// preemption, strongSelf still not nil（抢占的时候，strongSelf 还是非 nil 的)
 [strongSelf doSomethingElse]; // strongSelf != nil } 
else { // Probably nothing... return; 
}
};

ref:https://github.com/oa414/objc-zen-book-cn