NSInvocation的使用

http://blog.iosxcode4.com/?p=125

在 iOS中可以直接調用 某個對象的消息 方式有2種

一種是performSelector:withObject:

再一種就是NSInvocation

第一種方式比較簡單，能完成簡單的調用。但是對於>2個的參數或者有返回值的處理，那就需要做些額外工作才能搞定。那么在這種情況下，我們就可以使用NSInvocation來進行這些相對復雜的操作

NSInvocation可以處理參數、返回值。會java的人都知道反射操作，其實NSInvocation就相當於反射操作。

下面這個例子描述了如何使用NSInvocation，以下例子中如果要正常運行，需要把不存在的類進行正確填寫。

//方法簽名類，需要被調用消息所屬的類AsynInvoke ,被調用的消息invokeMethod:

NSMethodSignature *sig= [[AsynInvoke class] instanceMethodSignatureForSelector:@selector(invokeMethod:)];

//根據方法簽名創建一個NSInvocation

NSInvocation *invocation=[NSInvocation invocationWithMethodSignature:sig];

//設置調用者也就是AsynInvoked的實例對象，在這里我用self替代

[invocation setTarget:self];

//設置被調用的消息

[invocation setSelector:@selector(invokeMethod:)];

//如果此消息有參數需要傳入，那么就需要按照如下方法進行參數設置，需要注意的是，atIndex的下標必須從2開始。原因為：0 1 兩個參數已經被target 和selector占用

NSInteger num=10;

[invocation setArgument:&num atIndex:2];

//retain 所有參數，防止參數被釋放dealloc

[invocation retainArguments];

//消息調用

[invocation invoke];

//如果調用的消息有返回值，那么可進行以下處理

 

//獲得返回值類型

const char *returnType = sig.methodReturnType;

//聲明返回值變量

id returnValue;

//如果沒有返回值，也就是消息聲明為void，那么returnValue=nil

if( !strcmp(returnType, @encode(void)) ){

returnValue =  nil;

}

//如果返回值為對象，那么為變量賦值

else if( !strcmp(returnType, @encode(id)) ){

[invocation getReturnValue:&returnValue];

}

else{

//如果返回值為普通類型NSInteger  BOOL

 

//返回值長度

NSUInteger length = [sig methodReturnLength];

//根據長度申請內存

void *buffer = (void *)malloc(length);

//為變量賦值

[invocation getReturnValue:buffer];

 

 

if( !strcmp(returnType, @encode(BOOL)) ) {

returnValue = [NSNumber numberWithBool:*((BOOL*)buffer)];

}

else if( !strcmp(returnType, @encode(NSInteger)) ){

returnValue = [NSNumber numberWithInteger:*((NSInteger*)buffer)];

}

returnValue = [NSValue valueWithBytes:buffer objCType:returnType];

}

 

 

 

NSInvocation調用

CurrentDate.h

 
          #import  
          < 
          Foundation 
          / 
          Foundation.h 
          > 
          

@interface CurrentDate : NSObject {
 
}
 
          - 
           (NSString  
          * 
          ) stringForDate: (NSDate  
          * 
          )date 
 usingFormatter: (NSDateFormatter  
          * 
          )formatter;

@end 
         

CurrentDate.m

 
          #import  
          " 
          CurrentDate.h 
          " 
          

@implementation CurrentDate

 
          - 
           (NSString  
          * 
          ) stringForDate: (NSDate  
          * 
          )date 
 usingFormatter: (NSDateFormatter  
          * 
          )formatter
{
  
          return 
           [formatter stringFromDate: date];
}

@end 
         

main.m

 
          #import  
          < 
          Foundation 
          / 
          Foundation.h 
          > 
          
#import  
          " 
          CurrentDate.h 
          " 
          

 
          // 
          參考： 
          http://theocacao.com/document.page/264 
          
 
          int 
           main ( 
          int 
           argc,  
          const 
          char 
          * 
           argv[])
{

 NSAutoreleasePool  
          * 
           pool  
          = 
           [[NSAutoreleasePool alloc] init];

  
          // 
          原始調用 
          
 
           NSDateFormatter  
          * 
           dateFormat  
          = 
           [[NSDateFormatter alloc] 
 initWithDateFormat: 
          @" 
          %b %d %Y 
          " 
           
 allowNaturalLanguage: NO];
 CurrentDate  
          * 
           currentDateClassObject  
          = 
           [[CurrentDate alloc] init];
 NSString  
          * 
           currentDate  
          = 
           [currentDateClassObject 
 stringForDate: [NSDate date] 
 usingFormatter: dateFormat];
 NSLog( 
          @" 
          currentDate: %@ 
          " 
          , currentDate);
 
 
  
          // 
          NSInvocation調用 
          
 
           SEL mySelector  
          = 
           @selector(stringForDate:usingFormatter:);
 NSMethodSignature  
          * 
           sig  
          = 
           [[currentDateClassObject  
          class 
          ] 
 instanceMethodSignatureForSelector: mySelector];
 
 NSInvocation  
          * 
           myInvocation  
          = 
           [NSInvocation invocationWithMethodSignature: sig];
 [myInvocation setTarget: currentDateClassObject];
 [myInvocation setSelector: mySelector];
 
 NSDate  
          * 
           myDate  
          = 
           [NSDate date];
 [myInvocation setArgument:  
          & 
          myDate atIndex:  
          2 
          ];
 
 NSDateFormatter  
          * 
           dateFormatter  
          = 
           [[NSDateFormatter alloc] init];
 [dateFormatter setDateStyle: NSDateFormatterMediumStyle]; 
 [myInvocation setArgument:  
          & 
          dateFormatter atIndex:  
          3 
          ];
 
 NSString  
          * 
           result  
          = 
           nil; 
 [myInvocation retainArguments]; 
 [myInvocation invoke];
 [myInvocation getReturnValue:  
          & 
          result];
 NSLog( 
          @" 
          The result is: %@ 
          " 
          , result);
 

 [pool drain];
  
          return 
          0 
          ;
} 
         

 

http://www.j2megame.org/index.php/content/view/2635/165.html

NSMethodSignature和NSInvocation的使用

動態調用方法時會用到，例子 

-(NSString *)myMethod:(NSString *)param1 withParam2:(NSNumber *)param2 
{ 
    NSString *result = @"objc"; 
    NSLog(@"par = %@",param1); 
    NSLog(@"par 2 = %@",param2); 
    return result; 
} 


-(void)invokeMyMethodDynamically 
{ 
    SEL selector = @selector(myMethod:withParam2:); 
    NSMethodSignature *methodSignature = [[self class] instanceMethodSignatureForSelector:selector];//獲得類和方法的簽名 
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature]; 
    //從簽名獲得調用對象 
    [invocation setTarget:self]; 
    //設置target 
    [invocation setSelector:selector];//設置selector 
    NSString *returnValue = nil; 
    NSString *argument1 = @"fist"; 
    NSNumber *argument2 = [NSNumber numberWithInt:102]; 
    [invocation setArgument:&argument1 atIndex:2];//設置參數，第一個參數index為2 
    [invocation setArgument:&argument2 atIndex:3]; 
    [invocation retainArguments];//retain一遍參數 
    [invocation invoke];//調用 
    [invocation getReturnValue:&returnValue];//得到返回值，此時不會再調用，只是返回值 
    NSLog(@"return value = %@",returnValue); 
} 

另外一個例子:

SEL selector  =   @selector ( myMethod : setValue2 :);

NSMethodSignature   * signature  =   [ MyObject  instanceMethodSignatureF orSelector : selector ];
NSInvocation   * invocation  =   [ NSInvocation  invocationWithMethodSign ature : signature ];
[ invocation setSelector : selector ];

NSString   * str1  =   @ "someString" ;
NSString   * str2  =   @ "someOtherString" ;

//The invocation object must retain its arguments
[ str1 retain ];
[ str2 retain ];

//Set the arguments
[ invocation setTarget : targetInstance ];
[ invocation setArgument :& str1 atIndex : 2 ];
[ invocation setArgument :& str2 atIndex : 3 ];

[ NSTimer  scheduledTimerWithTimeIn terval : 0.1  invocation : invocation repeats : YES ]