NSInvocation的使用

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

在 iOS中可以直接调用 某个对象的消息 方式有2种

一种是performSelector:withObject:

再一种就是NSInvocation

第一种方式比较简单，能完成简单的调用。但是对于>2个的参数或者有返回值的处理，那就需要做些额外工作才能搞定。那么在这种情况下，我们就可以使用NSInvocation来进行这些相对复杂的操作

NSInvocation可以处理参数、返回值。会java的人都知道反射操作，其实NSInvocation就相当于反射操作。

下面这个例子描述了如何使用NSInvocation，以下例子中如果要正常运行，需要把不存在的类进行正确填写。

//方法签名类，需要被调用消息所属的类AsynInvoke ,被调用的消息invokeMethod:

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

//根据方法签名创建一个NSInvocation

NSInvocation *invocation=[NSInvocation invocationWithMethodSignature:sig];

//设置调用者也就是AsynInvoked的实例对象，在这里我用self替代

[invocation setTarget:self];

//设置被调用的消息

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

//如果此消息有参数需要传入，那么就需要按照如下方法进行参数设置，需要注意的是，atIndex的下标必须从2开始。原因为：0 1 两个参数已经被target 和selector占用

NSInteger num=10;

[invocation setArgument:&num atIndex:2];

//retain 所有参数，防止参数被释放dealloc

[invocation retainArguments];

//消息调用

[invocation invoke];

//如果调用的消息有返回值，那么可进行以下处理

 

//获得返回值类型

const char *returnType = sig.methodReturnType;

//声明返回值变量

id returnValue;

//如果没有返回值，也就是消息声明为void，那么returnValue=nil

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

returnValue =  nil;

}

//如果返回值为对象，那么为变量赋值

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

[invocation getReturnValue:&returnValue];

}

else{

//如果返回值为普通类型NSInteger  BOOL

 

//返回值长度

NSUInteger length = [sig methodReturnLength];

//根据长度申请内存

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

//为变量赋值

[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调用

CurrentDate.h

#import < Foundation / Foundation.h >

@interface CurrentDate : NSObject {

}
- (NSString * ) stringForDate: (NSDate * )date
usingFormatter: (NSDateFormatter * )formatter;

@end

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CurrentDate.m

#import " CurrentDate.h "

@implementation CurrentDate

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

@end

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main.m

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

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

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

// 原始调用
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调用
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 ;
}

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

NSMethodSignature和NSInvocation的使用

动态调用方法时会用到，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];//获得类和方法的签名      NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];      //从签名获得调用对象      [invocation setTarget:self];      //设置target      [invocation setSelector:selector];//设置selector      NSString *returnValue = nil;      NSString *argument1 = @"fist";      NSNumber *argument2 = [NSNumber numberWithInt:102];      [invocation setArgument:&argument1 atIndex:2];//设置参数，第一个参数index为2      [invocation setArgument:&argument2 atIndex:3];      [invocation retainArguments];//retain一遍参数      [invocation invoke];//调用      [invocation getReturnValue:&returnValue];//得到返回值，此时不会再调用，只是返回值      NSLog(@"return value = %@",returnValue);  }  另外一个例子: 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 ]