iOS中NSInvocation的使用
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];
}
-(void)popViewController:(id)sender{
if ([_callbackdic count]!=0&&[_callbackdic objectForKey:[_pushviewcontroller description]]!=nil) {
SEL sel=NSSelectorFromString([_callbackdic objectForKey:[_pushviewcontroller description]]);
NSMethodSignature *sig= [[_pushviewcontroller class] instanceMethodSignatureForSelector:sel];
NSInvocation *invocation=[NSInvocation invocationWithMethodSignature:sig];
[invocation setTarget:_pushviewcontroller];
[invocation setSelector:sel];
[_callbackdic removeObjectForKey:[_pushviewcontroller description]];
[invocation invoke];
return;
}
/*
if(_callbackselctor!=nil&&[_pushviewcontroller respondsToSelector:_callbackselctor]){
NSMethodSignature *sig= [[PlanList class] instanceMethodSignatureForSelector:_callbackselctor];
NSInvocation *invocation=[NSInvocation invocationWithMethodSignature:sig];
[invocation setTarget:_pushviewcontroller];
[invocation setSelector:_callbackselctor];
[invocation invoke];
_callbackselctor=nil;
return;
}00
*/
//清除出栈viewcontroller右侧按钮
int indexprevious=[[self viewControllers]count];
for (int i=0; i<[_rightviews count]; i++) {
UIButton*button=[_rightviews objectAtIndex:i];
if(indexprevious==button.tag){
[button removeFromSuperview];
[_rightviews removeObjectAtIndex:[_rightviews indexOfObject:button]];
}
}
if(_pushviewcontroller){
[_pushviewcontroller.navigationController popViewControllerAnimated:YES];
_pushviewcontroller=[[self viewControllers]lastObject];
}
//显示栈顶viewcontroller按钮
int index=[[self viewControllers]count];
for (UIButton* button in _rightviews) {
if(index==button.tag){
[button setHidden:NO];
}
}
if([[self viewControllers]count]<2)
[_backbutton setHidden:YES];
}