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, constchar* 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];
return0;
}
http://www.j2megame.org/index.php/content/view/2635/165.html
NSMethodSignature和NSInvocation的使用
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动态调用方法时会用到，例子 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] |