NSInvocation 是一个消息调用类， 用来调用某个类的某个方法
NSMethodSignature ： 方法签名，记录了方法的返回值的类型和参数的类型

例子

- (void)viewDidLoad
{
    [super viewDidLoad];
    SEL selector = @selector(addTextContent:atIndex:toContent:);
    //初始化一个方法签名，需要用Class去调，通过Class可以相应方法的返回值和参数的类型
    NSMethodSignature *signature = [[self class] instanceMethodSignatureForSelector:selector];
    NSLog(@"numberOfArguments:%ld", signature.numberOfArguments);
    for (NSInteger i=0; i<signature.numberOfArguments; i++) {
        
        const char * argumentType = [signature getArgumentTypeAtIndex:i];
        NSLog(@"argumentType: %@ index: %ld", [NSString stringWithUTF8String:argumentType], i);
    }
    //初始化NSInvocation
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
    invocation.target = self;
    invocation.selector = selector;

    //设置参数
    NSString *text = @"haa";
    NSNumber *index = @(10);
    NSString *content = @"content";

    //0代表target  1代表selector，已经被占用，所以从2开始
    [invocation setArgument:&text atIndex:2];
    [invocation setArgument:&index atIndex:3];
    [invocation setArgument:&content atIndex:4];
    
   //打印0和1位置的参数
    id __unsafe_unretained target;
    [invocation getArgument:&target atIndex:0];
    NSLog(@"target: %@", target);
    SEL sel;
    [invocation getArgument:&sel atIndex:1];
    NSLog(@"selector: %@", NSStringFromSelector(sel));

    //调用invocation执行方法
   [invocation invoke];

    //获取方法返回值
    NSArray * __unsafe_unretained tempResultSet;
    [invocation getReturnValue:&tempResultSet];
    NSArray *resultSet = tempResultSet;
    NSLog(@"%@", resultSet);
}

- (NSString *)addTextContent:(NSString *)text atIndex:(NSNumber *)index toContent:(NSString *)content
{
    return [NSString stringWithFormat:@"%@ %@ %@", text, index, content];
}

log打印

2018-09-29 15:59:03.257574+0800 testInvocation[44683:3741832] numberOfArguments:5
2018-09-29 15:59:03.257844+0800 testInvocation[44683:3741832] argumentType: @ index: 0
2018-09-29 15:59:03.257998+0800 testInvocation[44683:3741832] argumentType: : index: 1
2018-09-29 15:59:03.258135+0800 testInvocation[44683:3741832] argumentType: @ index: 2
2018-09-29 15:59:03.258311+0800 testInvocation[44683:3741832] argumentType: @ index: 3
2018-09-29 15:59:03.258414+0800 testInvocation[44683:3741832] argumentType: @ index: 4
2018-09-29 15:59:03.258646+0800 testInvocation[44683:3741832] target: <ViewController: 0x7fb1e8512c10>
2018-09-29 15:59:03.258796+0800 testInvocation[44683:3741832] selector: addTextContent:atIndex:toContent:
2018-09-29 15:59:03.259050+0800 testInvocation[44683:3741832] returnValue: haa 10 content