OC中反射机制的概念和使用

class反射

1: 通过类名的字符串形式实例化对象

Class class = NSClassFromString(@"Student");

Student *stu = [[class alloc] init];

2:将类名变为字符串

Class class = [Student class];

NSString *className = NSStringFromClass(class);

3:SEL反射

SEL selector = NSSelectorFromString(@"setName:");

[stu performSelector:selector withObject:@"zhang"];

4:将方法变成字符串

SEL selector = NSSelectorFromString(@"setName:");

    NSString *selectorName = NSStringFromSelector(selector);

    NSLog(@"selectorName: %@", selectorName);

    NSString *selectorName2 = NSStringFromSelector(@selector(setName:));

    NSLog(@"selectorName2: %@", selectorName2);

5:去除[stu performSelector:selector withObject:@"zhang"]的警告

<1.>    #pragma clang diagnostic push

            #pragma clang diagnostic ignored "-Warc-performSelector-leaks"

            [stu performSelector:selector withObject:@"zhang"];

            #pragma clang diagnostic pop

<2.>   定义一个宏

             #define SuppressPerformSelectorLeakWarning(Stuff) \

            do { \

            _Pragma("clang diagnostic push") \

            _Pragma("clang diagnostic ignored \"-Warc-performSelector-leaks\"") \    

            Stuff; \

            _Pragma("clang diagnostic pop") \

            } while(0)

        使用 ：SuppressPerformSelectorLeakWarning([stu performSelector:selector withObject:@"zhang"]);

6:什么是SEL？如何声明一个SEL？通过哪些方法能够调用SEL包装起来的方法？

<1> SEL就是对方法的一种包装。包装的SEL类型数据它对应的方法地址，找到方法地址就可以调用方法。在内存中每个类的方法都存储在类对象中，每个方法都有一个与之对应的SEL类型的数据，根据一个SEL数据就可以找到对应的方法地址，进而调用方法。

<2> SEL s1 = @selector(test1); // 将test1方法包装成SEL对象

<3> SEL s2 = NSSelectorFromString(@"test1"); // 将一个字符串方法转换成SEL对象

<4> 调用方法有两种方式

    直接通过方法名来调用[person text];

    间接的通过SEL数据来调用SEL aaa = @selector(text);[person performSelector:aaa];