ios - id a = [target performSelector:action withObject:params],a的值是什么

Question

我在网上找到一份关于组件化的代码,里面有这样一段代码

- (id)performTarget:(NSString *)targetName action:(NSString *)actionName params:(NSDictionary *)params shouldCacheTarget:(BOOL)shouldCacheTarget
{
    
    NSString *targetClassString = [NSString stringWithFormat:@"Target_%@", targetName];
    NSString *actionString = [NSString stringWithFormat:@"Action_%@:", actionName];
    
    id target = self.cachedTarget[targetClassString];
    if (target == nil) {
        Class targetClass = NSClassFromString(targetClassString);
        target = [[targetClass alloc] init];
    }
    
    SEL action = NSSelectorFromString(actionString);
    
    if (target == nil) {
        // 这里是处理无响应请求的地方之一，这个demo做得比较简单，如果没有可以响应的target，就直接return了。实际开发过程中是可以事先给一个固定的target专门用于在这个时候顶上，然后处理这种请求的
        return nil;
    }
    
    if (shouldCacheTarget) {
        self.cachedTarget[targetClassString] = target;
    }
    
    if ([target respondsToSelector:action]) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
        return [target performSelector:action withObject:params];
#pragma clang diagnostic pop
    } else {
        // 这里是处理无响应请求的地方，如果无响应，则尝试调用对应target的notFound方法统一处理
        SEL action = NSSelectorFromString(@"notFound:");
        if ([target respondsToSelector:action]) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
            return [target performSelector:action withObject:params];
#pragma clang diagnostic pop
        } else {
            // 这里也是处理无响应请求的地方，在notFound都没有的时候，这个demo是直接return了。实际开发过程中，可以用前面提到的固定的target顶上的。
            [self.cachedTarget removeObjectForKey:targetClassString];
            return nil;
        }
    }
}

其中让我困惑的代码片段是这句话

return [target performSelector:action withObject:params];

我查看这段代码的定义,返回的是一个id值

- (id)performSelector:(SEL)aSelector withObject:(id)object;

真实运行代码的时候,也是返回了想要的结果,如截图

但是问题来了,我自己运行代码的时候,却一直崩溃,我的代码如下:

    NSString *targetClassString = [NSString stringWithFormat:@"Test"];
    NSString *actionString = [NSString stringWithFormat:@"t"];
    
    Class targetClass = NSClassFromString(targetClassString);
    id target = [[targetClass alloc] init];
    
    SEL action = NSSelectorFromString(actionString);
    
    if ([target respondsToSelector:action]) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
        id a = [target performSelector:action withObject:nil];
        NSLog(@"%@",a);
#pragma clang diagnostic pop
    }

截图:

请问我是哪里配置有问题吗,还是哪里出错了,我现在没有头绪,希望大神们能帮帮忙

Answer 1

Um...I know, the value of id a is the return value of the method you define. If it returns empty, the printing will crash