IOS Property,Instance variable 傻傻分不清楚

Programming with Objective-C --- Encapsulating Data --- You Can Implement Custom Accessor Methods

Note: The compiler will automatically synthesize an instance variable in all situations where it’s also synthesizing at least one accessor method. If you implement both a getter and a setter for a readwrite property, or a getter for a readonly property, the compiler will assume that you are taking control over the property implementation and won’t synthesize an instance variable automatically.

If you still need an instance variable, you’ll need to request that one be synthesized:

@synthesize property = _property;

編譯器會自動合成你的property，如果你的R/W property 實作setter & getter，又或者你的R-Only property 實作了getter的話，編譯器會認為你已經做好property的控制，因此編譯器就不會幫你自動生成實體變數摟！！

如果你還是需要實體變數的話呢，你必須合成它

@synthesize property = _property;

難得找到OC的一些歷史，之前一直對Property和Instance variable分不清楚。

歷史：几个有用的Objective-C新特性

原來以前在宣告Property（name）的同時，還必須再宣告同名的Instance variable(_name)，最後再使用synthesize把這兩者關聯在一起（@synthesize name = _name;）

現在只要宣告一行Property就全部搞定了