两个NSInvocation崩溃引起的反思

淩亂°似流年 2022-02-13 12:51 288阅读 0赞

### 前言 ###

最近在使用NSInvocation进行多参数方法调用，结果就崩溃了！signature为nil 和 一直提示找不到方法！！！

`method signature argument cannot be nil` 崩溃信息：

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '+[NSInvocation _invocationWithMethodSignature:frame:]: method signature argument cannot be nil'
    *** First throw call stack:
    (0x1831a6d8c  .........)
    libc++abi.dylib: terminating with uncaught exception of type NSException

`unrecognized selector sent to instance`崩溃信息：

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ViewController openView]: unrecognized selector sent to instance 0x10510b1b0'
    *** First throw call stack:
    (0x1831a6d8c ......)
    libc++abi.dylib: terminating with uncaught exception of type NSException

原始示例代码：

- (void)myInvocation {
        
        SEL myMethod = @selector(sum:parm:parm:);
        //创建一个函数签名，这个签名可以是任意的,但需要注意，签名函数的参数数量要和调用的一致。
        NSMethodSignature * sig  = [[self class] instanceMethodSignatureForSelector:myMethod];
        //通过签名初始化
        NSInvocation * invocatin = [NSInvocation invocationWithMethodSignature:sig];
        //设置target
        [invocatin setTarget:self];
        //设置selecteor
        [invocatin setSelector:myMethod];
    
        int a=1;
        int b=2;
        int c=3;
        /*
         //index为2 是因为0、1两个参数已经被target和selector占用，其实可以这样设置：
         ViewController * view = self;
         [invocatin setArgument:&view atIndex:0];
         [invocatin setArgument:&myMethod atIndex:1];
         */
        [invocatin setArgument:&a atIndex:2];
        [invocatin setArgument:&b atIndex:3];
        [invocatin setArgument:&c atIndex:4];
        [invocatin retainArguments];
        //我们将c的值设置为返回值
        [invocatin setReturnValue:&c];
        int d;
        //取这个返回值
        [invocatin getReturnValue:&d];
        NSLog(@"%d",d);
    
        //消息调用
        [invocatin invoke];
        
    }
    
    + (int)sum:(int)a parm:(int)b parm:(int)c{
        NSLog(@"sum: %d:%d:%d",a,b,c);
        return a+b+c;
    }

### NSInvocation 注意项 ###

一直排查，开始以为是方法名写错了，认真一个一个字检查，没有错哦！！  
Way?!

不得而，还是在看看苹果文档！！！

--------------------

**instanceMethodSignatureForSelector:**

+ (NSMethodSignature *)instanceMethodSignatureForSelector:(SEL)aSelector;

> Returns an NSMethodSignature object that contains a description of the instance method identified by a given selector.

--------------------

**methodSignatureForSelector:**

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector;

> Returns an NSMethodSignature object that contains a description of the method identified by a given selector.

--------------------

#### 崩溃一 分析： ####

从苹果文档可以看到，生成NSMethodSignature对象有2个方法，一个是实例方法和一个类方法。

*  如果SEL是类方法要使用 **methodSignatureForSelector:**，
 *  如果SEL是实例方法就使用 **instanceMethodSignatureForSelector:**

所以，把`instanceMethodSignatureForSelector:` 改为`methodSignatureForSelector` 就解决啦！

#### 崩溃二 分析： ####

有了上面的分析，崩溃二是因为 `setTarget:`使用实例self，而类方法应用使用类，所以修改为`[invocatin setTarget:[self class]];`，就解决啦！

#### 最终代码： ####

- (void)myInvocation {
        
        SEL myMethod = @selector(sum:parm:parm:);
        //创建一个函数签名，这个签名可以是任意的,但需要注意，签名函数的参数数量要和调用的一致。
        NSMethodSignature * sig  = [[self class] methodSignatureForSelector:myMethod];
        //通过签名初始化
        NSInvocation * invocatin = [NSInvocation invocationWithMethodSignature:sig];
        //设置target
        [invocatin setTarget:[self class]];
        //设置selecteor
        [invocatin setSelector:myMethod];
    
        int a=1;
        int b=2;
        int c=3;
        /*
         //index为2 是因为0、1两个参数已经被target和selector占用，其实可以这样设置：
         ViewController * view = self;
         [invocatin setArgument:&view atIndex:0];
         [invocatin setArgument:&myMethod atIndex:1];
         */
        [invocatin setArgument:&a atIndex:2];
        [invocatin setArgument:&b atIndex:3];
        [invocatin setArgument:&c atIndex:4];
        [invocatin retainArguments];
        //我们将c的值设置为返回值
        [invocatin setReturnValue:&c];
        int d;
        //取这个返回值
        [invocatin getReturnValue:&d];
        NSLog(@"%d",d);
    
        //消息调用
        [invocatin invoke];
        
    }
    
    + (int)sum:(int)a parm:(int)b parm:(int)c{
        NSLog(@"sum: %d:%d:%d",a,b,c);
        return a+b+c;
    }

### 总结 ###

出现这样一个问题，直接说明平时没有关注文档和API实现，当前NSInvocation不常用，但是这次排查也用半天时间，有时候怀疑自己代码时，还是要从根本上找原因——— 从官方文档重新开始！

另外，复制网上的代码是一个危险的动作，不求甚解有时候坑就越深，希望自己以后不懂的知识要使用时，除了工期赶&复制，还要及时补充自己的空白，知其码，并知其然！努力成为一个优秀工程师！严谨！

### 参考引用 ###

*  [objective c - How can I invoke a class method by NSInvocation? - Stack Overflow][objective c - How can I invoke a class method by NSInvocation_ - Stack Overflow]
 *  [NSInvocation - Foundation | Apple Developer Documentation][NSInvocation - Foundation _ Apple Developer Documentation]
 *  [methodSignatureForSelector: - NSObject | Apple Developer Documentation][methodSignatureForSelector_ - NSObject _ Apple Developer Documentation]
 *  [instanceMethodSignatureForSelector: - NSObject | Apple Developer Documentation][instanceMethodSignatureForSelector_ - NSObject _ Apple Developer Documentation]

> 注：本文首发于 [iHTCboy's blog][iHTCboy_s blog]，如若转载，请注明来源。

[objective c - How can I invoke a class method by NSInvocation_ - Stack Overflow]: https://stackoverflow.com/questions/10900403/how-can-i-invoke-a-class-method-by-nsinvocation
[NSInvocation - Foundation _ Apple Developer Documentation]: https://developer.apple.com/documentation/foundation/nsinvocation
[methodSignatureForSelector_ - NSObject _ Apple Developer Documentation]: https://developer.apple.com/documentation/objectivec/nsobject/1571960-methodsignatureforselector?language=objc
[instanceMethodSignatureForSelector_ - NSObject _ Apple Developer Documentation]: https://developer.apple.com/documentation/objectivec/nsobject/1571959-instancemethodsignatureforselect?language=objc
[iHTCboy_s blog]: https://ihtcboy.com