Core OS:
Mach是一個由卡內基梅隆大學開發的用於支持操作系統研究的操作系統內核。
BSD (Berkeley Software Distribution，伯克利軟件套件)是Unix的衍生系統，在1977至1995年間由加州大學伯克利分校開發和發佈的。
Core Services
Media
Cocoa Touch
Model=What your application is (but not how it is displayed)
Controller=How your Model is presented to the user (UI logic)
View=Your Controller's minions
控制器可以直接和模型和視圖對話
模型和視圖不能對話
控制器設置自身爲視圖的委託
委託通過協議設置
視圖通過協議獲取控制器的數據
模型不能直接和控制器對話
The Model is UI independent
Properties
通常情況下OC我們不直接訪問實例變量
The getter (usually) has the name of the property (e.g. "myValue:")
The setter's name is "set" plus capitalized property name (e.g. "setMyValue:")
strong,weak,nonatomic區別
strong:
keep the object that property points to in memory until I set this property to nil
weak:
if no one else has a strong pointer to this object, then you can throw it out of memory and set this property to nil.
nonatomic:
access to this property is not thread-safe. we will always specify this for object pointers in this course. If you do not, then the compiler will generate locking code that will complicate your code elsewhere.
BOOL的就不需要申明strong還是weak，因爲primitive types are not strored in the heap.不是指針
@synthesize:表示creates the backing instance variable that is set and gotten.
- (NSString *)contents{
return _contents;
}
- (void)setContents:(NSString *)contents{
_contents = contents;
}