NSObject头文件解析 / 消息机制 / Runtime解读 (二)

本章接着NSObject头文件解析 / 消息机制 / Runtime解读(一)写

给类添加属性:

BOOL class_addProperty(Class cls, const char *name, const objc_property_attribute_t *attributes, unsigned int attributeCount)

其中有一个参数我们再在上一篇中提到过

typedef struct {

    const char *name;           /**< The name of the attribute */

    const char *value;          /**< The value of the attribute (usually empty) */

} objc_property_attribute_t;

我们看下常见的赋值

常用attribute	name	value
nonatomic	"N"	""
strong/retain	"&"	""
weak	"W"	""
属性的类型type	"T"	"@TypeName", eg"@"NSString""
属性对应的实例变量Ivar	"V"	"Ivar_name", eg "_name"
readonly	"R"	""
getter	"G"	"GetterName", eg"isRight"
setter	"S"	"SetterName", eg"setName"
assign/atomic	默认即为assign和retain

例子:

- (void)viewDidLoad {
    
    [super viewDidLoad];
    
    //创建一个对象
    ClassA *aClass = [ClassA new];
    
    
    //创建一个attributes
    objc_property_attribute_t nonatmoic = {"N", ""};
    objc_property_attribute_t strong    = {"&", ""};
    objc_property_attribute_t type      = {"T", "@"NSString""};
    objc_property_attribute_t ivar      = {"V", "_name"};
    
    objc_property_attribute_t attributes[] = {nonatmoic, strong, type, ivar, getter, setter};
    
    //给对象类添加属性
    BOOL result = class_addProperty([aClass class], "name", attributes, 4);
    
    if (result) {
        
        NSLog(@"添加成功");
    } else {
        
        NSLog(@"添加失败");
    }
    
    //读取添加属性
    objc_property_t property = class_getProperty([aClass class], "name");
    
    //获取添加的属性的名称
    NSString *propertyName = [NSString stringWithUTF8String:property_getName(property)];
    
    //打印获取到的属性名
    NSLog(@"获取到的属性名为: %@", propertyName);
    
}

运行结果:

2017-02-03 15:52:01.949 RunTimeDemo[786:37263] 添加成功
2017-02-03 15:52:01.949 RunTimeDemo[786:37263] 获取到的属性名为: name

替换属性:

void class_replaceProperty(Class cls, const char *name, const objc_property_attribute_t *attributes, unsigned int attributeCount)

例子:

//创建一个对象
    ClassA *aClass = [ClassA new];
    
    
    //创建一个attributes
    objc_property_attribute_t nonatmoic = {"N", ""};
    objc_property_attribute_t strong    = {"&", ""};
    objc_property_attribute_t type      = {"T", "@"NSString""};
    objc_property_attribute_t ivar      = {"V", "_name"};
    
    objc_property_attribute_t attributes[] = {nonatmoic, strong, type, ivar};
    
    //替换属性
    class_replaceProperty([aClass class], "name", attributes, 4);

运行时创建新类:

Class objc_allocateClassPair(Class superclass, const char *name, 
                                         size_t extraBytes)

注册创建的新类:

void objc_registerClassPair(Class cls) 

例子:

void printA(){
    
    NSLog(@"Print A");
}

- (void)viewDidLoad {
    
    [super viewDidLoad];
    
    //创新新类
    Class NewClass = objc_allocateClassPair([NSObject class], "NewObject", 0);
    
    //注册类
    objc_registerClassPair(NewClass);
    
    //给类添加方法
    class_addMethod([NewClass class], @selector(printA), (IMP)printA, "v@:");
    
    //创建实例
    id ob = [NewClass new];
    
    //实例执行方法
    [ob printA];
    
}

运行结果:

2017-02-03 18:11:34.091 RunTimeDemo[1114:96700] Print A

先Mark在这里, 后面会继续更新