在 iOS中可以直接調(diào)用 某個(gè)對(duì)象的消息 方式有2種

• performSelector:withObject:
• NSInvocation

第一種方式比較簡(jiǎn)單弧关，能完成簡(jiǎn)單的調(diào)用束莫。但是對(duì)于>2個(gè)的參數(shù)或者有返回值的處理，處理就相當(dāng)麻煩巷懈。
第二種NSInvocation也是一種消息調(diào)用的方法该抒，并且它的參數(shù)沒(méi)有限制，可以處理參數(shù)顶燕、返回值等相對(duì)復(fù)雜的操作凑保。

1.初始化使用

• 無(wú)參數(shù)無(wú)返回值

  - (void)invocation{
    //根據(jù)方法創(chuàng)建簽名對(duì)象sig
    NSMethodSignature *sign = [[self class] instanceMethodSignatureForSelector:@selector(method)];
    // 根據(jù)簽名對(duì)象創(chuàng)建調(diào)用對(duì)象invocation
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:sign];
    //設(shè)置target
    invocation.target = self;
    //設(shè)置selector
    invocation.selector = @selector(method);
    //消息調(diào)用
    [invocation invoke];
  }
  - (void)method {
      NSLog(@"method被調(diào)用");
  }
  

• 有參數(shù)無(wú)返回值

- (void)invocation{
  //根據(jù)方法創(chuàng)建簽名對(duì)象sig
  NSMethodSignature *sign = [[self class] instanceMethodSignatureForSelector:@selector(sendMessage:name:)];
  //根據(jù)簽名對(duì)象創(chuàng)建invocation
  NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:sign];

  //設(shè)置調(diào)用對(duì)象的相關(guān)信息
  NSString *name = @"張三";
  NSString *message = @"發(fā)送一條消息";

  //參數(shù)必須從第2個(gè)索引開始，因?yàn)榍皟蓚€(gè)已經(jīng)被target和selector使用
  [invocation setArgument:&name atIndex:2];
  [invocation setArgument:&message atIndex:3];
  invocation.target = self;
  invocation.selector = @selector(sendMessage:name:);
  //消息調(diào)用
  [invocation invoke];
}
- (void)sendMessage:(NSString*)message name:(NSString*)name{
    NSLog(@"%@ %@",name,message);
}

• 有參數(shù)有返回值

  - (void)invocation{
    //根據(jù)方法創(chuàng)建簽名對(duì)象sig
    NSMethodSignature *sign = [[self class] instanceMethodSignatureForSelector:@selector(sumNumber1:number2:)];
    //根據(jù)簽名創(chuàng)建invocation
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:sign];
    //設(shè)置調(diào)用對(duì)象相關(guān)信息
    invocation.target = self;
    invocation.selector = @selector(sumNumber1:number2:);
    NSInteger number1 = 30;
    NSInteger number2 = 10;
    [invocation setArgument:&number1 atIndex:2];
    [invocation setArgument:&number2 atIndex:3];
    //消息調(diào)用
    [invocation invoke];
  
    //獲取返回值
    NSNumber *sum = nil;
    [invocation getReturnValue:&sum];
  
    NSLog(@"總和==%zd",[sum integerValue]);
  }
  - (NSNumber*)sumNumber1:(NSInteger)number1 number2:(NSInteger)number2{
    NSInteger sum = number1+number2;
    return @(sum);
  }
  

2.常見方法及屬性

• NSInvocation其他常見方法屬性

 //保留參數(shù)涌攻，它會(huì)將傳入的所有參數(shù)以及target都retain一遍
- (void)retainArguments

// 判斷參數(shù)是否存在,調(diào)用retainArguments之前欧引，值為NO，調(diào)用之后值為YES
 @property (readonly) BOOL argumentsRetained;

 // 設(shè)置消息返回值
- (void)setReturnValue:(void *)retLoc;

• NSMethodSignature其他常見方法屬性

 // 方法參數(shù)個(gè)數(shù)
@property (readonly) NSUInteger numberOfArguments;

// 獲取方法的長(zhǎng)度
@property (readonly) NSUInteger frameLength;

// 是否是單向
- (BOOL)isOneway;

// 獲取方法返回值類型
@property (readonly) const char *methodReturnType NS_RETURNS_INNER_POINTER;

// 獲取方法返回值的長(zhǎng)度
@property (readonly) NSUInteger methodReturnLength;