NSInvocation的使用
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
@interface CurrentDate : NSObject {
}
- (NSString * ) stringForDate: (NSDate * )date
usingFormatter: (NSDateFormatter * )formatter;
@end
CurrentDate.m
@implementation CurrentDate
- (NSString * ) stringForDate: (NSDate * )date
usingFormatter: (NSDateFormatter * )formatter
{
return [formatter stringFromDate: date];
}
@end
main.m
#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 ;
}
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:
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 ]