IOS: Pass data back to previous view controller using completion block or closure

Question

From this answer there seems to be a way to pass data back to a prior View Controller using a Swift closure that is way simpler than using delegates.

Given that the Swift closure is similar to using blocks in Objective-C, how can I do this in my Objective-C project? I don't know Swift and delegate approach seems overly complicated to set one property.

Here is the Swift code:

For sending a UIImage back in my case. In ViewControllerA:

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    let cropImageViewController = segue.destinationViewController as! CropImageViewController
    cropImageViewController.choseImage = { image in
        //Do what you want in here!
    }
}
In ViewControllerB:

var choseImage : (UIImage -> Void)?
@IBAction func done(sender: AnyObject) {
    choseImage?(croppedImage)
    self.dismissViewControllerAnimated(true, completion: nil)
}

I can pass data forward using Prepare for Segue in Objective-C but am stumped on how to pass it backwards.

//launch VC
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ([segue.identifier isEqualToString:@"edit"]) {
...
destViewController.contact=contact;
}
//set property in presentingVC--THIS DOES NOT WORK. 

self.presentingViewController.afterSave = YES;
[self dismissViewControllerAnimated:YES completion:nil];

score 0 · Answer 1 · answered Nov 21 '16 at 05:51

Here is what you need to do in you crop view controller:

interface (.h):

@interface CropImageViewController : UIViewController

/// Block that returns void , called 'choseImage' and passes back UIImage.
@property (nonatomic,strong) void(^choseImage)(UIImage *image);

@end

implementation (.m):

@implementation CropImageViewController

-(void)done{

    // Check if block not nil
    if(self.choseImage){
        // Block usage with UIImage
        self.choseImage(croppedImage);
    }

}

@end

and in prepare for segue:

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{

    if ([segue.identifier isEqualToString:@"edit"]) {
        CropImageViewController *cropVC = [segue destinationViewController];
        [cropVC setChoseImage:^(UIImage *image) {
            // Use image
        }];
    }

}

IOS: Pass data back to previous view controller using completion block or closure

1 Answers1