iOS Runtime常见具体使用

一、Runtime介绍

Runtime是Objective-C的运行时库，由C和汇编实现。通过Runtime封装的C结构体和函数在运行时创建、检查、修改类及对象及其方法，甚至可以替换或交换方法的实现。使用runtime解决问题的好处经常是比较高效，而且不用导入头文件

二、项目里面的使用

1. 接口返回的NSDictionary里面有NSNull对象的情况。Method Swizzling

// 新建NSDictionary的category

- (id)nullObjectForKey:(id)attr{

return [[self nullObjectForKey:attr] isEqual:[NSNull null]] ? nil : [self nullObjectForKey:attr];

}

+ (void)load{

Method method1 = class_getInstanceMethod(self, @selector(objectForKey:));

Method method2 = class_getInstanceMethod(self, @selector(nullObjectForKey:));

method_exchangeImplementations(method1, method2);

}

2. 修改整个项目里面的字体，详见方法如下，这样可以做到放心的使用系统字体，实际上显示的是自定义字体

/**@return因为交换了方法实现，手动调用此方法返回的是系统字体。不建议主动去调用*/

+ (instancetype)wjFontOfSize:(CGFloat)fontSize{

return [UIFont fontWithName:@"STHeitiSC-Light" size:fontSize];

}

+ (void)load{

Method method1 = class_getClassMethod(self, @selector(systemFontOfSize:));

Method method2 = class_getClassMethod(self, @selector(wjFontOfSize:));

method_exchangeImplementations(method1, method2);

}

3. 动态属性关联，有时想在category关联一个属性（运行时无法动态添加属性）

//Cat+Extend.h

@interface Cat (extend)

@property(nonatomic, copy) NSString *name;

@end

//Cat+Extend.m

@implementation Cat (extend)

- (void)setName:(NSString *)name{

objc_setAssociatedObject(self, "name", name, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

}

- (NSString *)name{

return objc_getAssociatedObject(self, "name");

}

@end

4. 字典转模型时，遍历类的属性，给模型赋值。MJExtension里面是这样实现转模型的

5. 实现NSCoding的自动归档和自动解档

//解档

-  (instancetype)initWithCoder:(NSCoder*)aDecoder{

if(self= [super init]) {

Classc = self.class;

// 截取类和父类的成员变量

while(c && c != [NSObject class]) {

unsigned int count =0;

Ivar* ivars = class_copyIvarList(c, &count);

for(int i =0; i < count; i++) {

NSString *key = [NSString stringWithUTF8String:ivar_getName(ivars[i])];

id value = [aDecoder decodeObjectForKey:key];

if(value) {

[self setValue:value forKey:key];

}

}

// 获得c的父类

c = [c superclass];

free(ivars);

}

}

return self;

}

//归档

- (void)encodeWithCoder:(NSCoder*)aCoder{

Class c =self.class;

// 截取类和父类的成员变量

while(c && c != [NSObject class]) {

unsigned int count =0;

Ivar *ivars = class_copyIvarList(c,  &count);

for(int i =0; i < count; i++) {

Ivar ivar = ivars[i];

NSString*key = [NSString stringWithUTF8String:ivar_getName(ivar)];

id value = [self valueForKey:key];

[aCoder encodeObject:value forKey:key];

}

c = [c superclass];

// 释放内存

free(ivars);

}

}

三、引用文章：

1. iOS Runtime 几种基本用法简记