1.通过字符串创建类和对象
Class A = NSClassFromString(@"AAA");
id cls = [[NSClassFromString(@"ViewController") alloc]init];

2.通过类获取类名称字符串
NSString *str = NSStringFromClass(self);

3.通过字符串(已存在的方法名称)获取一个SEL
SEL selector = NSSelectorFromString(@"textFunc");

4.执行某个类的 每一个方法

//没有参数 类方法  返回值为BOOL
Class  AAA = NSClassFromString(@"WXSocialAgent");
    SEL selector = NSSelectorFromString(@"isWXAppInstalled");
    IMP imp = [AAA methodForSelector:selector];
    BOOL (*func)(Class, SEL) = (BOOL (*)(Class,SEL))imp;
    BOOL flag =  func(AAA,selector);

//有一个参数 类方法  无返回值
Class  AAA = NSClassFromString(@"WXSocialAgent");
    SEL selector = NSSelectorFromString(@"isWXAppInstalled");
    IMP imp = [AAA methodForSelector:selector];
    void (*func)(Class, SEL,id) = (void (*)(Class,SEL,id))imp;
    func(AAA,selector,@"abc");

//有多个参数 类方法  无返回值
Class  AAA = NSClassFromString(@"WXSocialAgent");
    SEL selector = NSSelectorFromString(@"isWXAppInstalled");
    IMP imp = [AAA methodForSelector:selector];
    void (*func)(Class, SEL,id,id) = (void (*)(Class,SEL,id,id))imp;
    func(AAA,selector,@"abc",@"ddf");

//有一个参数 实例方法  无返回值
    id  aaa = [[NSClassFromString(@"WXSocialAgent") alloc]init];
    SEL selector = NSSelectorFromString(@"isWXAppInstalled");
    IMP imp = [aaa methodForSelector:selector];
    void (*func)(id, SEL,id) = (void (*)(id,SEL,id))imp;
    func(aaa,selector,@"abc");

// 调用函数 有返回值
 id c = [[NSClassFromString(@"TestClass") alloc]init];
    SEL s = NSSelectorFromString(@"textFunction:");
    IMP imp = [c methodForSelector:s];
    void (*func)(Class, SEL,void(^)(NSString *)) = (void (*)(Class,SEL,void(^)(NSString *)))imp;
    if (c && [c respondsToSelector:s]) {
        func(c,s,^(NSString *string){
            NSLog(@"%@",string);
        });
    }