how to call tab bar view controller by click button function in swift

Question

I have one common tab bar view controller .And i have connected 3 other view controllers with navigation bar and i connect this 3 view controllers with the main tab bar view controller .So now i have 3 tab bar items with 3 view controller.

that is 1.Home 2. Cart 3. feedback

This is fine !!

And now my first view controller (That is my first tab bar view controller ) have some table view data and with detail view controller .And in my detail view controller i have one button called " Go to cart ".

So the actual flows is when user press Go to cart .It have to move to cart` view controller.Now its moving.

But the problem is .I was not able to see my tab bar items and other items .But if i go normal to each tab bar items its showing all tab bar items.

When i go from my Detail view button click to my Cart tab bar view controller..Then no tab bar items are showing down.

I did all this like demo prototype.Like i drag from button to cart tab bar view controller navigation bar.

But its not showing tab bar why.Please help me out.I don't have any single solution to solve this.I am using swift 2.2.

Thanks.

Updated :

So i need to code some thing like this Right?.But i don't know how to handle this code:

 let barViewControllers = sender.destinationViewController as! UITabBarController

    let nav = barViewControllers.viewControllers![1] as! UINavigationController

    let destinationViewController = nav.topViewController as! CartVC

But i am getting crash in first line :

fatal error: unexpectedly found nil while unwrapping an Optional value
(lldb) 

Please help me out

Answer 1

Here is storyboard similar to yours.

Now remove segue from button "go to cart" which is similar to "show second tab" button in my storyboard

Instead provide action to it as follows,

 @IBAction func showSecondTab(sender: AnyObject) {
            let  navController = self.tabBarController?.viewControllers![1] as! UINavigationController
            ///secondviewcontroller in your case is cart
            let secondViewController = navController.viewControllers[0] as! SecondViewController
            //set values you want to pass
            //lets say I want to pass name to secondVC
            secondViewController.name = "ABCD"

            self.tabBarController?.selectedIndex = 1
    }

you can print and check values in viewDidLoad of secondVC(CartVC).