随笔分类 -  Objective-C

• objc变量的获取
  摘要：【objc变量的获取】 C++成员变量通过偏移来寻找，速度极快。But Objc中的变量通过方法调用来寻找，方法首先根据变量名，找到ivar_t，然后在ivar_t对象中取出偏移，再用此偏移来取值（这最后一步和C++一样）。ivar_t类结构如下： objc-runtime中的object_... 阅读全文
  posted @ 2014-05-26 18:12 Tekkaman 阅读(297) 评论(0) 推荐(0)
• 当property遇上category
  摘要：【当property遇上category】 @property可以在类定义中，以及extension定义中使用，编译器会自动为@property生成代码，并在变量列表(ivar_list_t)中添加相应的以下划线开头的变量。 在category中，编译器允许定义@property，但不会为此@p... 阅读全文
  posted @ 2014-05-26 18:02 Tekkaman 阅读(897) 评论(0) 推荐(0)
• Effective ObjectiveC 2.0 Note
  摘要：【Effective ObjectiveC 2.0 Note】1、The memory for objects is always allocated in heap space and never on the stack。2、对于[NSArray arrayWithObjects：obj1,ob... 阅读全文
  posted @ 2014-05-25 19:59 Tekkaman 阅读(562) 评论(0) 推荐(0)
• key things of ARC
  摘要：【key things of ARC】1、使用原则。2、__weak变量的使用问题3、__autoreleasing的使用问题4、block中易造成的强引用环问题。5、栈变量被初始化为nil。6、在ARC下，不加修饰符的变量默认是strong。 阅读全文
  posted @ 2014-04-26 21:32 Tekkaman 阅读(195) 评论(0) 推荐(0)
• copyWithZone详解
  摘要：【copyWithZone详解】 NSObject实现了-copy、+copy、+copyWithZone方法。代码如下：+ (id)copy { return (id)self;}+ (id)copyWithZone:(NSZone *)zone { return (id)self;... 阅读全文
  posted @ 2014-04-14 16:28 Tekkaman 阅读(12858) 评论(0) 推荐(0)
• Collection Operators
  摘要：【Collection Operators】 Collectionoperators are specialized key paths that are passed as the parameter to thevalueForKeyPath:method. The operator is specified by a string preceded by an at sign (@). The key path on the left side of the collection operator, if present, determines the array or set, re. 阅读全文
  posted @ 2014-03-08 11:56 Tekkaman 阅读(320) 评论(0) 推荐(0)
• Accessor Search Implementation Details
  摘要：[Accessor Search Implementation Details] Key-value coding attempts to useaccessor methodsto get and set values, before resorting to directly accessing the instance variable. Key-value coding 优先使用accessor methods走获取与设置数据，之后再使直接访问instance variable.[Accessor Search Patterns for Simple Attributes] De... 阅读全文
  posted @ 2014-03-07 18:48 Tekkaman 阅读(738) 评论(0) 推荐(0)
• Tagged Pointers
  摘要：【Tagged Pointers】1、what is tagged pointer? 2、原理剖析 阅读全文
  posted @ 2014-02-23 17:40 Tekkaman 阅读(237) 评论(0) 推荐(0)
• New Objective-C Feature
  摘要：【Advance Objective-C Feature】1、@import避免反复解析头文件，本地宏对框架API定义无影响。 2、可以导入单独一个头文件。 3、使用了@import后，不再需要选择linked binary 4、#import与#include会默认使用@import 6、@import特性对compile和indexing的速度都有显著提升 7、@import默认会被打开 8、ios7, osx10.9以后才能用，只有内置框架才能使用此特性。 【Garbage Collection】 阅读全文
  posted @ 2014-02-23 17:29 Tekkaman 阅读(577) 评论(0) 推荐(0)
• Improved logging in Objective-C
  摘要：【Improved logging in Objective-C】 Example of logging the current method and line number. Paste it into your project, and see what it prints! Preprocessor macros and for logging in C/C++/Objective-C. 阅读全文
  posted @ 2014-02-23 11:10 Tekkaman 阅读(325) 评论(0) 推荐(0)
• Type Encoding
  摘要：【Type Encodings】 The compiler encodes the return and argument types for each method in a character string and associates the string with the method selector. 编译器把方法的返回值类型与参数类型encode成字符串，然后把此字符串与method selector关联起来。 When given a type specification, @encode() returns a string encoding that type. Th... 阅读全文
  posted @ 2014-02-22 19:47 Tekkaman 阅读(568) 评论(0) 推荐(0)
• Message Forwarding
  摘要：【Preprocess】 在使用forwarding机制前，会先经历2个步骤，只有当这2个步骤均失败的情况下，才会激活forwarding。1、+(BOOL)resolveInstanceMethod:(SEL)selector、resolveClassMethod。 当第一次没找到SEL时，调... 阅读全文
  posted @ 2014-02-16 23:12 Tekkaman 阅读(610) 评论(0) 推荐(0)
• Dynamic Method Resolution
  摘要：【Dynamic Method Resolution】 @dynamic directive 用于声明属性的方法dynamic loading，which tells the compiler that the methods associated with the property will be provided dynamically。即编译期不实现此方法，而由动态加载。此directive的作用在于告诉编译器某个类的实例拥有某属性而不会报编译错误。 You can implement the methods resolveInstanceMethod: and resolveCla.. 阅读全文
  posted @ 2014-02-16 22:43 Tekkaman 阅读(324) 评论(0) 推荐(0)
• Represent nil with NSNull
  摘要：【Represent nil with NSNull】 It’s not possible to add nil to the collection classes described in this section because nil in Objective-C means “no object.” If you need to represent “no object” in a collection, you can use the NSNull class:1 NSArray *array = @[ @"string", @42, [NSNull null] 阅读全文
  posted @ 2014-02-16 11:35 Tekkaman 阅读(405) 评论(0) 推荐(0)
• Encapsulating Data
  摘要：【Encapsulating Data】The synthesized methods follow specific naming conventions:The method used to access the value (thegettermethod) has the same name as the property. The getter method for a property calledfirstNamewill also be calledfirstName.The method used to set the value (thesettermethod) star 阅读全文
  posted @ 2014-02-16 10:16 Tekkaman 阅读(292) 评论(0) 推荐(0)
• Working with nil
  摘要：【Working with nil】 It’s always a good idea to initialize scalar variables at the time you declare them, otherwise their initial values will contain garbage from the previous stack contents: This isn’t necessary for object pointers, because the compiler will automatically set the variable to nil ... 阅读全文
  posted @ 2014-02-15 22:51 Tekkaman 阅读(299) 评论(0) 推荐(0)
• Determining Equality of Objects
  摘要：【Determining Equality of Objects】 If you need to determine whether one object is the same as another object, it’s important to remember that you’re working with pointers.The standard C equality operator == is used to test equality between the values of two variables, like this: When dealing with... 阅读全文
  posted @ 2014-02-15 21:45 Tekkaman 阅读(241) 评论(0) 推荐(0)
• NSLog中的%@
  摘要：【NSLog中的%@】 There is one additional substitution token available in Objective-C, %@, used to denote an object. At runtime, this specifier will be substituted with the result of calling either the descriptionWithLocale: method (if it exists) or the description method on the provided object. The desc. 阅读全文
  posted @ 2014-02-15 21:27 Tekkaman 阅读(2764) 评论(0) 推荐(0)
• 详解objc_msgSend
  摘要：【详解objc_msgSend】　1、为了性能，objc_msgSend用汇编写成。存在于objc-msg-x86_64.s中。 2、在上图代码中可以看到，objc_msgSend被分为2个过程：1）在cache中寻找SEL。2）在MethodTable寻找SEL。　3、CacheLookup中，不断地拿SEL与cache中的缓存比较，比较失败，则跳转到LCacheMiss标签继续在MethodTable中搜索。 如果想手动查找cache，则需要调用_cache_getimp函数（汇编实现），此函数是个对外接口层，用于保存与准备环境。 _cache_getImp在头文件中obj... 阅读全文
  posted @ 2013-05-23 11:34 Tekkaman 阅读(5628) 评论(1) 推荐(2)
• Mach-O Objc信息导出
  摘要：【Mach-O Objc信息导出】1、__DATA,__objc_selrefs 类型：SEL，指向 __TEXT,__objc_methname 中的数据长度：len(section)/len(SEL)注意：对于一个包含objc类信息的bundle，在bundle加载时，objc-runtime会把此bundle中的selrefs改写为指向__TEXT,__objc_methname中的数据。若该seg中数据不存在，存在在堆中新建一个字符串。简而言就是bundle中的selrefs不能指向自己的__TEXT seg。节省内存。2、__DATA,__objc_classlist &&a 阅读全文
  posted @ 2013-05-22 18:54 Tekkaman 阅读(886) 评论(0) 推荐(0)