phper初学objective-c之读书笔记(1)
phper初学objective-c之读书笔记(一)
基本语法:
static定义在全局变量上时会改变其作用域,对应所在的局部范围。extern类似php中的global。
结构体struct定义了一个多维kv数组,枚举类型enum检测数据范围,两者通过typedef可封装出自定义类型 。
*表示指针取值,&为取址操作(php中为引用传值,含义不同)。从实例化一个对象 NSString *foo=[NSString stringWithString:"example"] 可知,对象也是指针;指针取址后可通过运算操作地址。
带*的变量都寄存在heap,相反则在stack。
对象:
类中的方法又称消息,通常意义上调用一个方法,在oc中又称发送一个消息。
对象方法init用于初始化函数(相对于php的构造函数construct)。类方法即静态方法
私有方法放在实现文件中,调用方法之前
@sythesize会在编译时生成所需的setter、getter方法
property中的特性包括setter/getter、readwrite/readonly、assign/retain/copy、nonatomic
非线性安全noatomic不使用线程锁,性能略有提高;retain为指针拷贝,copy为内容拷贝,作用于NS对象
内存管理:
调用带有alloc、copy、create,使用类似[Foo alloc] init..]和CreateFoo()会使保留计数加1
通过autorelease在退出循环后会自动释放内存,但不是立刻释放;需要立刻释放使用[Foo release]形式,或创建自动释放池NSAutoreleasePool,再循环体尾部释放(drain或release),嵌套的释放池在最内部优先释放
init类似php的构造方法__construct,则dealloc则类似析构方法__destruct
oc中允许nil对象调用方法,结果为不执行,因此在释放成员变量后将指针设为nil,否则指向的内存地址会不存在(dangling pointer)
委托模式中对象互相内嵌会导致内存泄露,这时应该将委托变量设为assign类型的弱引用
属性的引用类型,强引用表明保留在内存中的指针,不被回收,弱引用反之
当nib文件中的对象没有被外部引用时,可能会被垃圾回收,因此创建一个强引用的IBOutlet连接到owner对象上

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