NSMethodSignature和NSInvocation使用

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