iOS NSInvocation的学习

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：

此Demo源码的下载链接。