如何从另一个视图 controller 保存数据并重新加载 tableview？

Question

I'm making an expense tracking app. I have added a table view in the main view controller, and added an "add" button in the navigation controller. On clicking this, it shows a view controller in which you type in the data. On clicking add at the end, it should save the entered data through coreData, and then be presented in the tableView, but my app crashes saying that a nil value was found, even though I have integrated the "??" safe guard. "

Answer 1

You tableview in startingViewController is nil this is the problem. When you call the MainVC.getAllItems() your tabview is not initialized. Probably you are re creating startingViewController on your second controller to reach it getAllItems function but it is a wrong approach. You need to update previous viewController datas with protocols or notifications.

First you need to create a protocol like below

protocol AddViewControllerDelegate {
func updateTableView() 
}

After that you need to define a variable in your addViewcontroller with this protocol type and call protocol's function when user adds new expense.

class AddViewController: UIViewController {

var delegate: AddViewControllerDelegate?

func callUpdateTableView() {
    delegate?.updateTableView()
}
}

In your StartingViewController must conform this protocol. So you need to add updateTableView function. Also you need to say the delegate of your second class is your first class in where you show your addViewController.

class StartingViewController: UIViewController, AddViewControllerDelegate {

func goToAddViewController() {
    let vc = AddViewController()
    vc.delegate = self
    show(vc, sender: nil)
}

func updateTableView() {
    // Reload Tableview
}
}

So basically, when you call the protocol function from your secondViewController, your firstViewController's updateTableView function called and you can reload your tableview in this function.