1、实例init方法
When I explained why I used variables instead of properties in the init method, I mentioned the gotcha of accidentally adding side effects if they provided implementations of those methods. However, another potential gotcha I didn’t mention is if someone subclasses your class, overrides the setter for your property, and adds a side effect, you have the same problem.
新建一个类，使用variables创建而不是使用properties创建init方法，一是因为如果该类提供了这些方法的实现（implementations），可能会产生副作用，比如在其它地方通过属性修改了变量的值。二是因为，如果别人继承了你的类，并重写了setter方法修改了你创建的属性，也是会产生潜在问题的。
二、对象释放须知
- (void)dealloc {
[_sushiTypes release];
_sushiTypes = nil;
[super dealloc];
}
Remember that when you created the array with alloc/init, it had a retain count of 1. So when you’re done with the array, you need to decrement the retain count. In Objective-C, you can do this by calling release on the object.
But where should you release it? Well, you should definitely release the array in dealloc, because obviously when this object is deallocated it will no longer need the array. Also, whenever you create an object in viewDidLoad (setting the reference count to 1), you should release the object in viewDidUnload. Don’t worry too much about this for now – some day I might write a separate memory management tutorial on that subject.
注意：
Note that you also set the object to nil afterwards. This is a good practice, because by setting it to nil it avoids a lot of problems. Any time you call a method on a nil object, it does nothing, but if you don’t set it to nil, if you tried calling a method on a deallocated object your program should crash.
三、Objective-C Cheat Sheet and Quick Reference
