how to return a function in objective-C

Question

I have several ViewControllers ,and a "networkClient" subclass of NSObject which offer functions of get/post data.

if "networkClient" occur an error when get/post data,the functions will return an error info for the ViewControllers who call get/post functions.

I found I always have lots of same code in different ViewControllers, such as:

- (void)showAlertWithString:(NSString *)string{
    SIAlertView *alertView = [[SIAlertView alloc]initWithTitle:@"Error" andMessage:string];
    [alertView addButtonWithTitle:@"OK" 
    type:SIAlertViewButtonTypeDestructive handler:^(SIAlertView *alertView){
    }];
    [alertView show];
}

since I don't want to include the 3rd party library "SIAlertView" and write the code -(void)showAlertViewWithString in every ViewControllers.

I'm wondering is there a way to include the library and write the code only in "networkClient" and return this -(void)showAlertViewWithString to the ViewControllers and let them execute it in the ViewControllers when the error happened?

update: thanks for the answers, as I'm a beginner of iOS development I just know there's a method called 'block' and after I tried, it seemed work.

below is the code which I tried to use block instead delegate to call "show alert" in ViewControllers.

AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
NSDictionary *parameters = @{@"action" : @"create_user",
                             @"email" : email,
                             @"password" :password,
                             @"user_name" :name,
                             @"mobile": number
                             };
[manager POST:kLoginURL
   parameters:parameters
      success:^(AFHTTPRequestOperation *operation, id responseObject) {
          SIAlertView *alertView = [[SIAlertView alloc]initWithTitle:@"Alert" andMessage:@"Success"];
          [alertView addButtonWithTitle:@"ok" type:SIAlertViewButtonTypeDestructive handler:^(SIAlertView *alertView){

          }];
          [alertView show];
      }
//              [self.delegate createAccountResult:(responseObject)];
      failure:^(AFHTTPRequestOperation *operation, NSError *error) {
          NSLog(@"Error: %@", error);
      }];
}

Try to subclass the UIViewController with your networkClient in it so you can handle the success/error blocks. — SleepNot
– SleepNot, Commented Feb 10, 2015 at 1:57
I have read some articles about using a block, I found that I could just write the function I want to execute in the block and it will execute in the ViewControllers which call the "networkClient"method. — Don Chen
– Don Chen, Commented Feb 10, 2015 at 2:50

Duncan C · Accepted Answer · 2015-02-10 01:57:51Z

1

So create a custom subclass of UIViewController, and implement that method in the class. Then make all your view controllers inherit from your custom class.

Alternately you could create a category of UIViewController.

answered Feb 10, 2015 at 1:57

Duncan C

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2 Comments

Don Chen Over a year ago

yes~! that's a good idea I used to try this, it is very useful when several ViewControllers use same functions. I also heard about "block" maybe it is a better choice when I have already created the ViewControllers....>_<.... I should learn about how to use block...

Duncan C Over a year ago

Blocks are very useful, but I'm not sure how they would apply here.

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