How to get the previous viewcontroller that pushed my current view

Question

The home page of my app has UIButtons, btnIncome and btnExpense. Pressing on this buttons pushes IncomeVC and ExpenseVC respectevely,which are two UIViewControllers with UITabBar added via xib. The tabBar have 4 items. Selecting on each tab item adds same four view controllers(which contains UITableViews) as the subview of IncomeVC and ExpenseVC,like for eg, DailyVC,WeeklyVC,MonthlyVC,YearlyVC.(ie,for Income ,there is daily,weekly etc and same for Expense) (I have done like that because the IncomeVC and ExpenseVC have a UIButton and a UIView which is common for all tabs).

So the problem is that, if click the btnIncome I have to populate those tableviews with the arrays related to Income and vice versa for Expense. How can I find from which viewController I selected the different tabs(I need to get it from the 4 Views I added as the subview of IncomeVC and ExpenseVC). Do I have to make 8 different views 4 each for Income and expense ? Thanx.

Solution 1

If the reason for needing access to the previous view controller is to know what data to get, I would suggest that you instead give the new view controller the data before you push it on the stack. Or at least enough data so that the view controller know how to get the right data, e.g. a enum or constant or something.

This could be done with a custom initializer, or a property. Take a look at this blog post for an example: "Passing Data Between View Controllers"

If you are using a storyboard, you can use prepareForSegue:sender to pass the right data. A good tutorial on that can be found here: Beginning Storyboards in iOS 5 Part 2

Solution 2

In Swift 3,

if let navController = self.navigationController, navController.viewControllers.count >= 2 {
     let viewController = navController.viewControllers[navController.viewControllers.count - 2]
}

Solution 3

You can get the previous viewController like following code,

NSLog(@"%@",[self.navigationController.viewControllers objectAtIndex:self.navigationController.viewControllers.count-2]);

This will displays the previous viewController name...

Solution 4

In Swift:

let n: Int! = self.navigationController?.viewControllers?.count
let myUIViewController = self.navigationController?.viewControllers[n-2] as! UIViewController

Solution 5

Swift 3

Here is a mashup of the previous answers that can be put into an extension:

extension UIViewController{
   var previousViewController:UIViewController?{
        if let controllersOnNavStack = self.navigationController?.viewControllers, controllersOnNavStack.count >= 2 {
            let n = controllersOnNavStack.count
            return controllersOnNavStack[n - 2]
        }
        return nil
    }
}

Edit:

When fetching the previousViewController of a given view controller, call it VC1, in viewWillDisappear, VC1 is already popped of the Navigation Controller Stack. So in this scenario, the above code does not end up fetching the View controller directly above VC1(call it VC2), but the view controller above VC2 (if it exists).

To avoid this problem I just check if VC1 is still on the stack when previousViewController is requested. Here is the updated code:

extension UIViewController{
    var previousViewController:UIViewController?{
        if let controllersOnNavStack = self.navigationController?.viewControllers{
            let n = controllersOnNavStack.count
            //if self is still on Navigation stack
            if controllersOnNavStack.last === self, n > 1{
                return controllersOnNavStack[n - 2]
            }else if n > 0{
                return controllersOnNavStack[n - 1]
            }
        }
        return nil
    }
}

This code assumes that view controller you are sending the previousViewController message to will either be at the top of the navigation stack or not at all.

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Comments

[Cyprian]

@Erik count property is always greater by 1 then the index so to get the UIViewController before the current UIViewController you must subtract 2 from the count

[baquiax]

It's unsafe access directly n-2 because if you are the first VC you will have an error. Maybe you can use an previous validation.

[J.beenie]

Is it possible to have a situation in which the view controller being viewed is not on the top of the navigation stack?

[RubenVot]

Potential crash due to array out of bounds

[RubenVot]

I obviously know and that's the reason why I downvoted. You should fix your code or add the comment warning other people that your code is insecure. btw, I upvoted you answer for Swift 3