用途：
NSInvocation的作用和performSelector:withObject:的作用是一样的：用于iOS编程中调用某个对象的消息。
performSelector:withObject:调用一些参数较少的消息是比较方便的，但是对于参数个数大于2的消息，使用NSInvocation还是比较方便的。
因为NSInvocation是静态的呈现Objective-C的消息，也就是说，它把一个行动变成了一个对象。NSInvocation对象用于对象之间和应用程序之间存储和转发消息，主要通过NSTimer对象和分布式对象系统来完成。
代码：
//
// NSInvocation+Improved.h
// InvocationDemo
//
// Created by 李振杰 on 13-12-11.
// Copyright (c) 2013年 swplzj. All rights reserved.
// #import <Foundation/Foundation.h> @interface NSInvocation (Improved) + (NSInvocation *)invocationWithTarget:(id)_target andSelector:(SEL)_selector;
+ (NSInvocation *)invocationWithTarget:(id)_target andSelector:(SEL)_selector andArguments:(void *)_addressOfFirstArgument, ...;
- (void)invokeOnMainThreadWaitUntilDone:(BOOL)wait; @end
//
// NSInvocation+Improved.m
// InvocationDemo
//
// Created by 李振杰 on 13-12-11.
// Copyright (c) 2013年 swplzj. All rights reserved.
// #import "NSInvocation+Improved.h" @implementation NSInvocation (Improved) + (NSInvocation *)invocationWithTarget:(id)_target andSelector:(SEL)_selector
{
//方法签名类
//需要给定一个方法，用于必须创建一个NSInvocation对象的情况下，例如在消息的转发。
NSMethodSignature *methodSig = [_target methodSignatureForSelector:_selector];
//根据方法签名类来创建一个NSInvocation
/*
一个NSInvocation是静态的呈现Objective-C的消息，也就是说，它是一个行动变成了一个对象。 NSInvocation对象用于对象之间和在应用程序之间存储和转发消息，主要通过NSTimer对象和分布式对象系统来完成。
*/
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
[invocation setTarget:_target];
[invocation setSelector:_selector];
return invocation;
} + (NSInvocation *)invocationWithTarget:(id)_target andSelector:(SEL)_selector andArguments:(void *)_addressOfFirstArgument, ...
{
NSMethodSignature *methodSig = [_target methodSignatureForSelector:_selector];
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
[invocation setTarget:_target];
[invocation setSelector:_selector];
//获得签名类对象的参数个数
unsigned int numArgs = [methodSig numberOfArguments];
//PS:atIndex的下标必须从2开始。原因：0 1 两个参数已经被target 和selector占用
if (2 < numArgs) {
/*
VA_LIST 是在C语言中解决变参问题的一组宏，所在头文件：#include <stdarg.h>
VA_START宏，获取可变参数列表的第一个参数的地址（ap是类型为va_list的指针，v是可变参数最左边的参数）
VA_ARG宏，获取可变参数的当前参数，返回指定类型并将指针指向下一参数（t参数描述了当前参数的类型）
VA_END宏，清空va_list可变参数列表
*/ /*
用法：
（1）首先在函数里定义一具VA_LIST型的变量，这个变量是指向参数的指针；
（2）然后用VA_START宏初始化刚定义的VA_LIST变量；
（3）然后用VA_ARG返回可变的参数，VA_ARG的第二个参数是你要返回的参数的类型（如果函数有多个可变参数的，依次调用VA_ARG获取各个参数）；
（4）最后用VA_END宏结束可变参数的获取。
*/
va_list varargs; va_start(varargs, _addressOfFirstArgument);
[invocation setArgument:_addressOfFirstArgument atIndex:2]; for (int argIndex = 3; argIndex < numArgs; argIndex++) {
void *argp = va_arg(varargs, void *);
[invocation setArgument:argp atIndex:argIndex];
} va_end(varargs);
}
return invocation;
} - (void)invokeOnMainThreadWaitUntilDone:(BOOL)wait
{
[self performSelectorOnMainThread:@selector(invoke) withObject:nil waitUntilDone:wait];
} @end
自定义类：
//
// SomeClass.h
// InvocationDemo
//
// Created by 李振杰 on 13-12-11.
// Copyright (c) 2013年 swplzj. All rights reserved.
// #import <Foundation/Foundation.h> @interface SomeClass : NSObject - (void)commonOperation;
- (void)improvedOperation;
- (void)fireTimer:(NSDictionary *)user andDate:(NSDate *)startTime; @end
//
// SomeClass.m
// InvocationDemo
//
// Created by 李振杰 on 13-12-11.
// Copyright (c) 2013年 swplzj. All rights reserved.
// #import "SomeClass.h"
#import "NSInvocation+Improved.h" @implementation SomeClass - (void)commonOperation
{
NSDate *date = [NSDate date];
NSDictionary *user = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", nil];
SEL method = @selector(fireTimer:andDate:);
NSMethodSignature *signature = [[self class] instanceMethodSignatureForSelector:method];
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
[invocation setTarget:self];
[invocation setSelector:method];
[invocation setArgument:&user atIndex:2];
[invocation setArgument:&date atIndex:3];
// [NSTimer scheduledTimerWithTimeInterval:0.1 invocation:invocation repeats:YES];
[invocation invoke];
} - (void)improvedOperation
{
//1.创建一个没有参数的NSInvocation
// SEL selector = @selector(fireTimer:andDate:);
// NSInvocation *invocation = [NSInvocation invocationWithTarget:self andSelector:selector]; //2.创建带有两个参数的NSInvocation
NSDate *date = [NSDate date];
NSDictionary *user = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", nil];
NSInvocation *invocation = [NSInvocation invocationWithTarget:self andSelector:@selector(fireTimer:andDate:) andArguments:&user, &date];
[invocation invoke];
} - (void)fireTimer:(NSDictionary *)user andDate:(NSDate *)startTime
{
/*
sleep 与 sleepForTimeInterval的区别
sleep直接让线程停掉，sleepForTimeInterval是让runLoop停掉。比如说，你有2个APP，分别是A和B，A启动B，然后去取B的进程号，如果你用sleep等B启动再去取，你会发现取不到，因为你只是把代码加到runloop里面去，而runloop并没有执行到这句，sleep就直接让系统停在那里，所以取不到，而后者就没问题，因为它是让runloop执行到这句的时候停1s
*/ [NSThread sleepForTimeInterval:2];
NSTimeInterval timeInterval = -1 * [startTime timeIntervalSinceNow];
NSString *timeStr = [NSString stringWithFormat:@"%.2f", timeInterval];
NSLog(@"fireTime: %@", timeStr);
} @end
调用SomeClass：
//
// AppDelegate.m
// InvocationDemo
//
// Created by 李振杰 on 13-12-11.
// Copyright (c) 2013年 swplzj. All rights reserved.
// #import "AppDelegate.h"
#import "SomeClass.h" @implementation AppDelegate - (void)dealloc
{
[_window release];
[super dealloc];
} - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
// Override point for customization after application launch. SomeClass *some = [[SomeClass alloc] init];
[some commonOperation];
[some improvedOperation];
[some release]; self.window.backgroundColor = [UIColor whiteColor];
[self.window makeKeyAndVisible];
return YES;
} @end
Demo源码：