具有返回值的iOS块

Question

我正在使用Facebook SDK中的一个块.它返回一个字典.我希望该字典作为方法的返回值.我试图围绕整个街区的概念,但需要在正确的方向轻推.

块:(块的参数是字符串userFBid)

-(NSDictionary*) getMutualFBFriendsWithFBid:(NSString*)fbID {

[FBRequestConnection startWithGraphPath:[NSString stringWithFormat:@"/%@/mutualfriends/%@", [[PFUser currentUser] objectForKey:kFbID],userFBid]
                    parameters:nil
                             HTTPMethod:@"GET"
                      completionHandler:^(
                                          FBRequestConnection *connection,
                                          id result,
                                          NSError *error
                                          ) {
                          result = (NSDictionary*)result;

//return result;                              
       }];

}

我如何获得返回值？

我试图谷歌它,但我无法抓住它.

我会很感激任何指针在正确的方向.

编辑: 主要问题如下:我需要完成处理程序来调用另一个类中的方法...如何做到这一点？

Answer 1

由于该方法startWithGraphPath是异步的,您不能将其编码为同步:它意味着没有返回值,因为一旦调用此方法,您的应用程序将继续执行到下一行,并且不会等待返回值.

所以,为了保持这种异步,我假设你想在你自己的函数中使用它的结果,所以在你的completionHandler块中调用它:

[FBRequestConnection startWithGraphPath:[NSString stringWithFormat:@"/%@/mutualfriends/%@", [[PFUser currentUser] objectForKey:kFbID],userFBid]
                             parameters:nil
                             HTTPMethod:@"GET"
                      completionHandler:^(FBRequestConnection *connection, id result, NSError *error) {
                          [self myRockinFunction:result];
       }];

//Considering this function 
-(void)myRockinFunction:(NSDictionary*) fb_result{
    //Do stuff with fb_result
}

编辑

好的我明白了.修改您的方法以接受回调作为参数:

-(NSDictionary*) getMutualFBFriendsWithFBid:(NSString*)fbID andCallback:(void (^)(NSDictionary *))callback {

    [FBRequestConnection startWithGraphPath:[NSString stringWithFormat:@"/%@/mutualfriends/%@", [[PFUser currentUser] objectForKey:kFbID],userFBid]
                    parameters:nil
                             HTTPMethod:@"GET"
                      completionHandler:^(FBRequestConnection *connection,id result,NSError *error) {
         //You should treat errors first
         //Then cast the result to an NSDictionary
         callback((NSDictionary*) result); //And trigger the callback with the result
    }];
}

然后,在您的其他类中,使用另一个块来处理您的结果:

[YourHelperClass getMutualFBFriendsWithFBid:fbID andCallback:^(NSDictionary* result){
    //Use result how you wish
    //Beware, this is async too.
}];

注意:您应该在触发回调之前处理错误.

编辑2(其他用户的帮助表示赞赏)

更好的是,你可能会尝试传递一个带有所有参数的回调(没有经过测试,也不确定语法.如果有人可以纠正我,我会很感激):

-(NSDictionary*) getMutualFBFriendsWithFBid:(NSString*)fbID andCallback:(void (^)(FBRequestConnection *,NSDictionary *,NSError *))callback {

    [FBRequestConnection startWithGraphPath:[NSString stringWithFormat:@"/%@/mutualfriends/%@", [[PFUser currentUser] objectForKey:kFbID],userFBid]
                    parameters:nil
                             HTTPMethod:@"GET"
                      completionHandler:callback()]; //Not sure here!
}

[YourHelperClass getMutualFBFriendsWithFBid:fbID andCallback:^(FBRequestConnection *connection,NSDictionary * result,NSError *error){
     //You could deal with errors here now
}];

以下是有关Apple更深入理解的文档的参考资料.