Passing value from table view controller to view controller

I tried to pass the value of the cell that the user clicks on to another view controller.

Here is my code.

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    productDisplayed = currentProductList[indexPath.row] as? Product
    performSegue(withIdentifier: "ProductDetailSegue", sender: self)
}


override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if ( segue.identifier == "AddProductSegue"){
        let controller: AddProductViewController = segue.destination as! AddProductViewController
        controller.delegate = self
    }

    if ( segue.identifier == "ProductDetailSegue"){

        let controller: ProductDetailsViewController = segue.destination as! ProductDetailsViewController
        controller.currentProduct = productDisplayed
    }
}

Firstly, I didn’t write “performSegue()”. The issue I met is that the screen will be transferred firstly rather than assign the value to “productDisplayed”, which means the object “currentProduct” in the second VC is nil.

Then I added “performSegue()”. It still didn’t work. The thing is the second screen was displayed twice. The first time is same with the picture above. And the second time is correct.

But when I tried to click the back button on the left top. It returned to the nil page rather than the ProductDetail page. The screenshot is as follows.

It seems like "prepare" method always being called first then the tableView. How to change the order? If can, this should be fixed I think.

Hope to get your help. Thank you.