NSMethodSignature和NSInvocation使用，消息转发的时候用的到。
#import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController
-(void)method1Test
{
NSLog(@"method1Test");
}
-(NSInteger)mehtod2Test
{
NSLog(@"method2Test");
return 1;
}
-(ViewController*)method3Test:(NSString*)str
{
NSLog(@"参数:%@",str);
return self;
}
- (void)viewDidLoad
{
[super viewDidLoad];
[self nsInvocationTest];
}
-(void)nsInvocationTest
{
//无参数，无返回值
//通过选择器获取方法签名
SEL selector = @selector(method1Test);
NSMethodSignature *methodSign = [[self class] instanceMethodSignatureForSelector:selector];
//通过方法签名获得调用对象
NSInvocation *methodInvocation = [NSInvocation invocationWithMethodSignature:methodSign];
[methodInvocation setTarget:self];
[methodInvocation setSelector:selector];
[methodInvocation invoke];
//有返回值，无参数
selector = @selector(mehtod2Test);
methodSign = [[self class] instanceMethodSignatureForSelector:selector];
NSInvocation *mehtod2Invocation = [NSInvocation invocationWithMethodSignature:methodSign];
[mehtod2Invocation setSelector:selector];
[mehtod2Invocation invokeWithTarget:self];
NSInteger returnValue = 0;
[mehtod2Invocation getReturnValue:&returnValue];
NSLog(@"返回值:%ld",returnValue);
//有返回值，有参数
selector = @selector(method3Test:);
NSMethodSignature *method3Sign = [[self class] instanceMethodSignatureForSelector:selector];
NSInvocation *method3Invocation = [NSInvocation invocationWithMethodSignature:method3Sign];
[method3Invocation setTarget: self];
[method3Invocation setSelector:selector];
NSString *arg1 = @"testArg1";
[method3Invocation setArgument:&arg1 atIndex:2];
[method3Invocation invoke];
//当返回值为对象是，arc情况下容易出现崩溃问题，如下两种解决方案。arc下vc如果用strong的，默认NSInvocation实现认为，已经对返回对象retain一次，实际上并没有，当返回对象出了作用域时候，已经被收回。导致崩溃。
解决方案1
void *vc = nil;
[method3Invocation getReturnValue:&vc];
NSLog(@"vc:%@",(__bridge ViewController*)vc);
解决方案1
UIViewController * __unsafe_unretained vc = nil;
[method3Invocation getReturnValue:&vc];
NSLog(@"vc:%@",vc);
}
@end
