Send message from swift ViewController to objective c ViewController

Question

I have a ViewController in objective c (PhotoEditViewController) that instantiates a ViewController in swift (ColorPickerViewController):

- (IBAction)colorButtonPress:(id)sender {
    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:
                                @"Main" bundle:[NSBundle mainBundle]];
    UIViewController *colorController = [storyboard instantiateViewControllerWithIdentifier:@"colorPickerPopover"];
    colorController.modalPresentationStyle = UIModalPresentationPopover;
    colorController.preferredContentSize = CGSizeMake(284, 446);

    // Get the popover presentation controller and configure it.
    UIPopoverPresentationController *presentationController = [colorController popoverPresentationController];
    presentationController.sourceView = sender;
    presentationController.sourceRect = CGRectMake(0, 0, 85, 30);
    presentationController.permittedArrowDirections = UIPopoverArrowDirectionAny;
    presentationController.delegate = self;

    [self presentViewController:colorController animated:YES completion:nil];

}

This is what the ColorPickerViewController looks like:

import UIKit

class ColorPickerViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

// Global variables
var tag: Int = 0
var color: UIColor = UIColor.gray
var delegate: PhotoEditViewController? = nil

// This function converts from HTML colors (hex strings of the form '#ffffff') to UIColors
func hexStringToUIColor (_ hex:String) -> UIColor {
    var cString:String = hex.trimmingCharacters(in: .whitespacesAndNewlines).uppercased()

    if (cString.hasPrefix("#")) {
        cString.remove(at: cString.startIndex)
    }

    if (cString.characters.count != 6) {
        return UIColor.gray
    }

    var rgbValue:UInt32 = 0
    Scanner(string: cString).scanHexInt32(&rgbValue)

    return UIColor(
        red: CGFloat((rgbValue & 0xFF0000) >> 16) / 255.0,
        green: CGFloat((rgbValue & 0x00FF00) >> 8) / 255.0,
        blue: CGFloat(rgbValue & 0x0000FF) / 255.0,
        alpha: CGFloat(1.0)
    )
}

// UICollectionViewDataSource Protocol:
// Returns the number of rows in collection view
internal func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 10
}
// UICollectionViewDataSource Protocol:
// Returns the number of columns in collection view
internal func numberOfSections(in collectionView: UICollectionView) -> Int {
    return 16
}
// UICollectionViewDataSource Protocol:
// Inilitializes the collection view cells
internal func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) 
    cell.backgroundColor = UIColor.clear
    cell.tag = tag
    tag = tag + 1

    return cell
}

    // Recognizes and handles when a collection view cell has been selected
    internal func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {

        var colorPalette: Array<String>

        // Get colorPalette array from plist file
        let path = Bundle.main.path(forResource: "colorPalette", ofType: "plist")
        let pListArray = NSArray(contentsOfFile: path!)

        if let colorPalettePlistFile = pListArray {
            colorPalette = colorPalettePlistFile as! [String]

            var cell: UICollectionViewCell  = collectionView.cellForItem(at: indexPath)! as UICollectionViewCell
            var hexString = colorPalette[cell.tag]
            color = hexStringToUIColor(hexString)
            self.view.backgroundColor = color
            NSLog("Send delegate message")
            delegate?.setButtonColor(color) // THIS IS WHAT ISN'T BEING CALLED
        }
    }
}

The problem I am having is that the method .setButtonColor() isn't being called. I have declared this method in the PhotoEditViewController.h:

- (void)setButtonColor:(UIColor*) color;

and I also have it in the PhotoEditViewController.mm file:

- (void)setButtonColor:(UIColor*) color {
    NSLog(@"color");
}

Answer 1

You have to cast the colorController as ColorPickerViewController. When you're trying to set the colorController.delegate = self PhotoEditViewController thinks that colorController is generic UIViewController class and it doesn't know that it has a delegate variable.

instead of

UIViewController *colorController = [storyboard instantiateViewControllerWithIdentifier:@"colorPickerPopover"];

you need to do

ColorPickerViewController *colorController = [storyboard instantiateViewControllerWithIdentifier:@"colorPickerPopover"];

This lets PhotoEditViewController know that colorController is type of ColorPickerViewController and it has all those stored variables and delegates.

Answer 2

Change the implementation of you colorButtonPressed: action to this:

- (IBAction)colorButtonPress:(id)sender {
    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:
                            @"Main" bundle:[NSBundle mainBundle]];

    // Change the class of from UIViewController to ColorPickerViewController while instantiating
    ColorPickerViewController *colorController = [storyboard instantiateViewControllerWithIdentifier:@"colorPickerPopover"];

    // Set the delegate
    colorController.delegate = self;
    colorController.modalPresentationStyle = UIModalPresentationPopover;
    colorController.preferredContentSize = CGSizeMake(284, 446);

    // Get the popover presentation controller and configure it.
    UIPopoverPresentationController *presentationController = [colorController popoverPresentationController];
    presentationController.sourceView = sender;
    presentationController.sourceRect = CGRectMake(0, 0, 85, 30);
    presentationController.permittedArrowDirections = UIPopoverArrowDirectionAny;
    presentationController.delegate = self;

    [self presentViewController:colorController animated:YES completion:nil];
}