具有返回值的iOS块 [英] iOS block with return value
问题描述
块：
（块的参数是一个字符串userFBid）
- （NSDictionary *）getMutualFBFriendsWithFBid：（NSString *）fbID {
[ FBRequestConnection startWithGraphPath：[NSString stringWithFormat：@/％@ / mutualfriends /％@，[[PFUser currentUser] objectForKey：kFbID]，userFBid]
参数：nil
HTTPMethod：@GET
completionHandler：^（
FBRequestConnection * connection，
id result，
NSError * error
）{
result =（NSDictionary *）result;
//返回结果;
}];
}
返回值？
我已经尝试google了，但我不能让我的手。
我会感激任何指向正确的方向。
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？
由于方法 startWithGraphPath 是异步的，您无法编码好像它是同步的：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，并且不会等待返回的值。
所以，为了保持这个异步，我假设你想在你自己的函数中使用这个结果，所以在你的 completionHandler 块中调用它：
[FBRequestConnection startWithGraphPath：[NSString stringWithFormat：@/％@ / mutualfriends /％@，[[PFUser currentUser] objectForKey ：kFbID]，userFBid]
参数：nil
HTTPMethod：@GET
completionHandler：^（FBRequestConnection * connection，id result，NSError * error）{
[self myRockinFunction ：结果];
}];
//考虑这个函数
- （void）myRockinFunction：（NSDictionary *）fb_result {
//用fb_result
进行填充
编辑
好的，我明白了修改你的方法接受回调作为一个参数：
- （NSDictionary *）getMutualFBFriendsWithFBid：（NSString *）fbID andCallback :( void（^）（NSDictionary *））callback {
[FBRequestConnection startWithGraphPath：[NSString stringWithFormat：@/％@ / mutualfriends /％@，[[PFUser currentUser] objectForKey：kFbID]，userFBid ]
参数：nil
HTTPMethod：@GET
completionHandler：^（FBRequestConnection * connection，id result，NSError * error）{
//你应该先处理错误
//然后将结果转换为NSDictionary
回调（（NSDictionary *）结果）; //并触发回调结果
}];
}
然后，在其他类中，使用另一个块来对待您的结果： / p>
[YourHelperClass getMutualFBFriendsWithFBid：fbID andCallback：^（NSDictionary * result）{
//使用结果如何希望
//当心，这也是异步的。
}];
注意：您应该在触发回调之前对待错误。
编辑2（来自其他用户的帮助赞赏）
更好的是，您可能会尝试传递所有参数的回调（未测试，而不是确定语法，如果有人可以纠正我，我会感激）：
- （NSDictionary *）getMutualFBFriendsWithFBid：（NSString *）fbID andCallback：（void（^）（FBRequestConnection *，NSDictionary *，NSError *））callback {
[FBRequestConnection startWithGraphPath：[NSString stringWithFormat：@/％@ / mutualfriends /％@ ，[[PFUser currentUser] objectForKey：kFbID]，userFBid]
参数：nil
HTTPMethod：@GET
completionHandler：callback（）]; //不确定在这里
}
[YourHelperClass getMutualFBFriendsWithFBid：fbID andCallback：^（FBRequestConnection * connection，NSDictionary * result，NSError * error）{
//你现在可以处理这里的错误
}];
这是Apple的文档的参考，以便更深入地了解。
I am using a block from Facebook SDK. It returns a dictionary. I want that dictionary as a return value of a method. I am trying to wrap my head around the whole block concept but need a nudge in the right direction.
The block: (the argument for the block is a string 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;
}];
}
How do i get the return value?
I have tried to google it, but i cant get my hand around it.
I would appreciate any pointer in the right direction.
EDIT: The main question is the following: I need to the completion handler to call a method in another class... how to do that?
As the method startWithGraphPath is asynchronous, you can't code as if it was synchronous : it means no return value, because as soon as this method is called, your app will continue to execute to the next line, and won't wait for a returned value.
So, to keep this async, I assume you want to use the result of this in your own function, so call it in your completionHandler block:
[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
}
Edit
OK, I get it. Modify your method to accept a callback as a parameter :
-(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
}];
}
Then, in your other class, use another block to treat your result :
[YourHelperClass getMutualFBFriendsWithFBid:fbID andCallback:^(NSDictionary* result){
//Use result how you wish
//Beware, this is async too.
}];
Note : you should treat the error before triggering your callback.
Edit 2 (Help from other users appreciated)
Even better, you might try to pass a callback taking all the parameters (not tested, and not sure of the syntax. If someone can correct me, I'd appreciate):
-(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
}];
Here's a reference on Apple's docs for deeper understanding.
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