OC Runtime特性让他具有一些新功能，可以应用在日常的工作中，下面介绍 Runtime 中常见的应用，可以简要总结为以下几点（都要用到<objc/runtime.h>库）：
- 方法交换（Method Swizzle)
- 给分类（Category）添加属性
- 实现类的自动归档和自动解档
- 实现字典转模型
方法交换（Method Swizzle)
就是利用以下方法（来自<objc/runtime.h>库）：
// 获得某个类的实例对象方法
Method class_getInstanceMethod(Class cls , SEL name)
// 获得某个类的类方法
Method class_getClassMethod(Class cls , SEL name)
// 交换两个方法的实现
void method_exchangeImplementations(Method m1 , Method m2)
例子：
@interface Person : NSObject
- (void)speak;
- (void)run;
@end
@implementation Person
- (void)speak {
NSLog(@"%s", __func__);
}
- (void)run {
NSLog(@"%s", __func__);
}
@end
Person *person = [[Person alloc] init];
Method m1 = class_getInstanceMethod([Person class], @selector(speak));
Method m2 = class_getInstanceMethod([Person class], @selector(run));
method_exchangeImplementations(m1, m2);
[person speak]; // -[Person run]
[person run]; // -[Person speak]
给分类（Category）添加属性
如果没有runtime，分类只能在运行时给类添加方法，不能添加实例变量，可以添加属性，但添加的属性没有getter和setter，只有扩展（extension）能再编译时给类添加方法、属性、实例变量（都是私有的），有了runtime，可以使用关联对象（Associated Object），为分类的属性添加getter和setter，具体为：
// 为一个实例对象添加一个关联对象，用键key（字符串）来区分（可以是一个属性的名称），value为具体的关联对象的值，policy为存储策略（比如copy,strong等）
void objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy);
// 通过实例对象和key，获取关联对象的值
id objc_getAssociatedObject(id object, const void *key);
// 删除实例对象的关联对象
void objc_removeAssociatedObjects(id object);
// objc_AssociationPolicy的定义如下
typedef OBJC_ENUM(uintptr_t, objc_AssociationPolicy) {
OBJC_ASSOCIATION_ASSIGN = 0, /**< Specifies a weak reference to the associated object. */
OBJC_ASSOCIATION_RETAIN_NONATOMIC = 1, /**< Specifies a strong reference to the associated object.
* The association is not made atomically. */
OBJC_ASSOCIATION_COPY_NONATOMIC = 3, /**< Specifies that the associated object is copied.
* The association is not made atomically. */
OBJC_ASSOCIATION_RETAIN = 01401, /**< Specifies a strong reference to the associated object.
* The association is made atomically. */
OBJC_ASSOCIATION_COPY = 01403 /**< Specifies that the associated object is copied.
* The association is made atomically. */
};
例子：
@interface Person (Name)
@property(copy) NSString *personMame;
@end
@implementation Person (Name)
-(void) setPersonMame:(NSString *)personMame {
objc_setAssociatedObject(self, "personMame", personMame, OBJC_ASSOCIATION_COPY);
}
-(NSString *) personMame {
return objc_getAssociatedObject(self, "personMame");
}
@end
Person *person = [[Person alloc] init];
person.personMame = @"Danny";
NSLog(@"%@", person.personMame); // Danny
实现类的自动归档和自动解档
要实现自动归档和解档，需要知道一个类的所有属性名称，在runtime中有如下实现方法：
// 获得某个类的所有成员变量，返回在一个列表中
Ivar *class_copyIvarList(Class cls , unsigned int *outCount)
// 获得成员变量的名字
const char *ivar_getName(Ivar v)
例子：
@interface Person : NSObject
@property (copy) NSString *gender;
@property (assign) int age;
- (instancetype)initWithCoder:(NSCoder *)aDecoder;
- (void)encodeWithCoder:(NSCoder *)aCoder;
@end
@implementation Person
- (instancetype)initWithCoder:(NSCoder *)aDecoder {
// 获取所有成员变量
if (self = [super init]) {
unsigned int outCount = 0;
Ivar *ivars = class_copyIvarList([self class], &outCount);
for (int i = 0; i < outCount; i++) {
Ivar ivar = ivars[i];
// 将每个成员变量名转换为NSString对象类型
NSString *key = [NSString stringWithUTF8String:ivar_getName(ivar)];
// 根据变量名解档取值，无论是什么类型
id value = [aDecoder decodeObjectForKey:key];
// 取出的值再设置给属性
[self setValue:value forKey:key];
// 这两步就相当于以前的 self.age = [aDecoder decodeObjectForKey:@"_age"];
}
free(ivars);
}
return self;
}
- (void)encodeWithCoder:(NSCoder *)aCoder {
unsigned int outCount = 0;
Ivar *ivars = class_copyIvarList([self class], &outCount);
for (int i = 0; i < outCount; i++) {
Ivar ivar = ivars[i];
// 将每个成员变量名转换为NSString对象类型
NSString *key = [NSString stringWithUTF8String:ivar_getName(ivar)];
// 通过成员变量名，取出成员变量的值
id value = [self valueForKeyPath:key];
// 再将值归档
[aCoder encodeObject:value forKey:key];
}
free(ivars);
}
@end
int main(int argc, const char *argv[])
{
@autoreleasepool {
Person *person = [[Person alloc] init];
person.age = 21;
person.gender = @"male";
// 定义归档文件路径
NSString *pathPerson = [NSString stringWithFormat:@"%@/Documents/person", NSHomeDirectory()];
// 调用归档函数
[NSKeyedArchiver archiveRootObject:person toFile:pathPerson];
//新建一个实例，来接受解归档的数据
Person *personOut = [NSKeyedUnarchiver unarchiveObjectWithFile:pathPerson];
NSLog(@"%d", personOut.age); // 21
NSLog(@"%@", personOut.gender); // male
}
return 0;
}
实现字典转模型
遍历模型的所有的属性，再去字典中根据属性名找对应值进行赋值
例子：
@interface Person : NSObject
@property (copy) NSString *gender;
@property (assign) int age;
- (void)setDict:(NSDictionary *)dict;
@end
@implementation Person
- (void)setDict:(NSDictionary *)dict {
Class c = self.class;
while (c && c != [NSObject class]) {
unsigned int outCount = 0;
Ivar *ivars = class_copyIvarList(c, &outCount);
for (int i = 0; i < outCount; i++) {
Ivar ivar = ivars[i];
NSString *key = [NSString stringWithUTF8String:ivar_getName(ivar)];
// 成员变量名转为属性名（去掉下划线 _ ）
key = [key substringFromIndex:1];
// 取出字典的值
id value = dict[key];
// 如果模型属性数量大于字典键值对数理，模型属性会被赋值为nil而报错
if (value == nil) continue;
// 将字典中的值设置到模型上
[self setValue:value forKeyPath:key];
}
free(ivars);
c = [c superclass];
}
}
@end
int main(int argc, const char *argv[])
{
@autoreleasepool {
Person *person = [[Person alloc] init];
NSDictionary *dictionary = @{
@"age": @21,
@"gender": @"male"
};
[person setDict:dictionary];
NSLog(@"%d", person.age); // 21
NSLog(@"%@", person.gender); // male
}
return 0;
}
