Interface should be changed before time-consuming task starts in Swift-CodePudding

I'm trying to implement the following behaviour of collectionView cell: by tapping on the cell the appearance of the cell should be changed first! And AFTER that, a time-consuming process should start:

@objc private func addItemsToBasket(_ button: UIButton) {
         button.setTitleColor(.clear, for: .normal)
         Basket.addItems(keys: planner.currentDayKeys())
}

but unfortunately, the cell changes appearance only after the time-consuming block is finished. If I comment "Basket.addItems(keys: planner.currentDayKeys())" the cell changes its appearance prompt.

I have already tried different options in GCD, nothing helped. But actually, if I don't define a Queue the code should run line by line. Right?

It should be a very common case. Thank you in advance for any ideas.

CodePudding user response：

Like mentioned in the comments, you should not perform time consuming tasks on the main queue. GCD will definitely help you in this case. Have you tried something like this:

@objc private func addItemsToBasket(_ button: UIButton) {
    button.setTitleColor(.clear, for: .normal)
    DispatchQueue.global.async {
        Basket.addItems(keys: self.planner.currentDayKeys())
    }
}

But you need to make sure that if you do some UI changes in your Basket.addItems, you need to dispatch them back to main by wrapping them inside a DispatchQueue.main.async closure.