IOS, a modified four key variables, namely:
This keyword is modified variables are completely open, as long as this kind of object exists, you can access to this variable.
This keyword is modified variables are protected, only in this class it is declared and its subclasses can be accessed.
This keyword is modified variables are private and can only be used in the class declaration of this variable, the subclass can not be used.
This keyword is more difficult to understand, roughly meaning the variable is modified package can be freely used within this framework, the same effect and @public, but can not be used outside the framework of its subclasses can not use, but the effect is equivalent to @private.
Because @package of this feature, it is very suitable for franework framework.
Access class variables, we can use the -> symbol, the difference between it and the point is that the grammar, the syntax is actually a set point and get method call, and -> symbols are directly accessible variables.