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NSInvocation

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消息发送

在iOS中不通过类可以直接调用某个对象的消息方式有两种：

  1. performSelector:withObject;
  2. NSInvocation

performSelector使用

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@implementation HTOtherModule

- (void)doSomethingWithParameter:(NSString *)para{
    NSLog(@"done some with:%@",para);
}

@end

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Class cls = NSClassFromString(@"HTOtherModule");
id obj = [[cls alloc]init];
[obj performSelector:NSSelectorFromString(@"doSomethingWithParameter:") withObject:@"this is the value"];

performSelector虽然能达到调用方法的目的，但是传递的参数最多只能有两个，也许可以通过封装进字典来传递，但是这样就徒增了工作。我们可以用NSInvocation的特性来达到这个目的。

NSInvocation

NSInvocation与其他NSObject类不一样，不会通过alloc/init来生成，它需要通过一个方法签名NSMethodSignature来生成

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NSInvocation *invocatin = [NSInvocation invocationWithMethodSignature:sig];

而NSMethodSignature由类的selector来形成的

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NSMethodSignature *sig  = [cls instanceMethodSignatureForSelector:aSelecotor];

依次填补参数，

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[invocatin setTarget:obj];
[invocatin setSelector:aSelecotor];
NSString *para = @"this is the value";
[invocatin setArgument:&para atIndex:2];

触发，就可以发送一条消息

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[invocatin invoke];

下面是调用HTOtherModule类的方法的完整代码：

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SEL aSelecotor = NSSelectorFromString(@"doSomethingWithParameter:");
   Class cls = NSClassFromString(@"HTOtherModule");
   id obj = [[cls alloc]init];
   NSMethodSignature * sig  = [cls instanceMethodSignatureForSelector:aSelecotor];
   NSInvocation * invocatin = [NSInvocation invocationWithMethodSignature:sig];
   [invocatin setTarget:obj];
   [invocatin setSelector:aSelecotor];
   NSString *para = @"this is the value";
   [invocatin setArgument:&para atIndex:2];
   [invocatin invoke];

组件化路由跳转（Mediator）

Category

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@interface HTMediator (HTOtherModule)

- (NSString *)otherModulePerform:(NSString *)targetName action:(NSString *)actionName name:(NSString *)name hour:(NSUInteger)hour place:(NSString *)palce doSomething:(NSString *)doSomething;

@end
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- (id)performTarget:(NSString *)targetName action:(NSString *)actionName parameters:(NSArray *)parameters{
    Class tagetClass = NSClassFromString(targetName);
    NSObject *tagert= [[tagetClass alloc]init];
    SEL aSelector = NSSelectorFromString(actionName);
    NSMethodSignature *methodSignature = [tagetClass instanceMethodSignatureForSelector:aSelector];
    if(methodSignature == nil) // 方法签名找不到，异常情况自己处理
    {
        NSLog(@"找不到这个方法");
        return nil;
    }
    else
    {
        NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];
        [invocation setTarget:tagert];
        [invocation setSelector:aSelector];
        
        //消息发送的参数，签名两个是class和selector，所以方法参数从第3个开始
        [parameters enumerateObjectsUsingBlock:^(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
            [invocation setArgument:&obj atIndex:idx+2];
        }];
        [invocation invoke];
        
        //返回值处理
        __autoreleasing id callBackObject = nil;
        if(methodSignature.methodReturnLength)
        {
            [invocation getReturnValue:&callBackObject];
        }
        return callBackObject;
    }
    return nil;
}

参考

  1. Runtime应用(三)：NSInvocation