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];
}
}
