iOS 运行时

1、OC的消息机制

SEL又叫选择器，是表示一个方法的selector的指针.可以通过 Objc 编译器器命令@selector() 或者 Runtime 系统的 sel_registerName 函数来获取一个 SEL 类型的方法选择器.
IMP实际上是一个函数指针，指向方法实现的地址.

 objc_msgSend(obj, @selector (method));//发送消息

 SEL selector= @selector (method);
[self performSelector: NSSelectorFromString(@” method”)]; 
[self performSelector:@selector( NSSelectorFromString(@” method”):) withObject:@"传入参数"];

//NSString*methodName = NSStringFromSelector(selector);
IMP methodPoint = [self methodForSelector: selector];
//IMP methodPoint = [self instanceMethodForSelector: selector];
methodPoint();

2、方法交换

   void method_exchangeImplementations(Method m1, Method m2)

首先建一个NSObject类目NSObject+ExchangeMethod，在类目中为NSObject类扩展一个my_dealloc方法用于替换系统的dealloc方法，其.m文件实现如下：

+(void)load{
    Method m1=class_getInstanceMethod(self,NSSelectorFromString(@"dealloc"));
    Method m2=class_getInstanceMethod(self,@selector(my_dealloc));
    method_exchangeImplementations(m1,m2);
}

-(void)my_dealloc{
    NSLog(@"mydealloc");
    [self my_dealloc];
}

3、动态添加方法

DynamicAdd *add=[DynamicAdd alloc]init];
//[add addMethod];
[add performSelector:@selector(addMethod)]]; //避免编译错误

DynamicAdd中没有实现addMethod方法,运行时会因为找不到addMethod出现闪退.这个时候可以通过动态添加方法解决闪退问题.

#import "DynamicAdd.h"
#import <objc/message.h>

void test(id self,SEL _cmd){
     NSLog("开发测试动态添加方法");
}

//当前对象找不到方法,回调执行该类方法,此时动态添加方法
+(BOOL)resolveClassMethod:(SEL)sel{
       if(sel == NSSelectorFromString(@"addMethod")){
            class_addMethod(self,see,(IMP)test,@"v@:");
            return YES;
       }
    return [super resolveClassMethod:sel];
}

//如果动态添加方法失败会继续执行forwardingTargetForSelector


- (id)forwardingTargetForSelector:(SEL)aSelector {
  
    NSString *selectorString = NSStringFromSelector(aSelector);
 
    // 将消息转发给_helper来处理;在helper里实现addMethod方法
    if ([selectorString isEqualToString:@"addMethod"]) {
        return _helper;
    }
 
    return [super forwardingTargetForSelector:aSelector];
}

 

4、动态添加属性

#import<Foundation/Foundation.h>
@interface NSObject(Property)
@property NSString *name;
@end


#import "NSObject+Property.h"
#import <objc/message.h>

@implementation NSObject(Property)
-(void)setName:(NSString *)name{
    objc_setAssociatedObject(self,"name",name,OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

-(NSString *)name{
    return objc_getAssociatedObject(self,"name");
}
@end

5、获取类中的成员变量和属性

unsigned int count;
Ivar *ivars=class_copyIvarList([UIButton class],&count);
for(int i=0; i<count;i++){
     Ivar ivar = ivars[i];
     NSString *name = [NSString stringWithUTF8String:ivar_getName(ivar)];
     NSString  *type = [NSString stringWithUTF8String:ivar_getTypeEncoding(ivar)];
     NSLog(@"%@---%@",type,name);
}

6、消息转发

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
    NSMethodSignature *signature = [super methodSignatureForSelector:aSelector];
 
    if (!signature) {
        if ([Helper instancesRespondToSelector:aSelector]) {
            signature = [Helper instanceMethodSignatureForSelector:aSelector];
        }
    }
 
    return signature;
}
 
- (void)forwardInvocation:(NSInvocation *)anInvocation {
    if ([Helper instancesRespondToSelector:anInvocation.selector]) {
        [anInvocation invokeWithTarget:_helper];
    }
}