I am using a Replace style segue in UISplitViewController's DetailViewController. My question is - when I replace the VC with the "replace segue", where goes the old one, does it get destroyed? If so, how can I re-instantiate the previous VC, the segue doesn't point both ways, does it?
Reason: I am trying to make TWO Detail Views that swap depending on the row clicked in the UITable in the Master View.
So you want to keep the replaced view controller?
Do you ARC? If you do, then keep a strong reference to both view controllers. That should prevent them from being "destroyed".
If you don't then retain both view controller objects. That prevents them from being released until the release count is zero and then being deallocated.
When you re-display the now-not-destroyed view controller, make sure that you really reuse the existing object. Do not create a new one. (Most tutorials etc. should create a new one each time).
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I made an app for my wife to track inventory. it has a couple of view controllers to enter a new item, display all items, search items, and display selected item. After switching through each view a couple of times (no particular order) all of the textfields become disabled (you cannot select them to change the value) across ALL of the view controllers. The buttons still work however. I have it setup so that when the user enters info into a particular cell, it saves it into memory so that if they switch views and then come back, the cells will get the data in the viewdidload method. Please Help!
*edit - I am using storyboard with a bunch of segues (i'm new to programming and self taught, so idk if this is the right way or not)... here is a pic of my storyboard
http://i.imgur.com/aT3PR0i.png
Ok, with a look at your storyboard, I think I see your problem. If your storyboard looks like somebody spilled spaghetti on it, it's not designed correctly. Specifically, it looks like you're going "backwards" (to controllers you've already been to) using segues -- that's not good. SEGUES ALWAYS INSTANTIATE NEW CONTROLLERS! So, if you go around in a circle a few times, you're adding more and more controllers to your project. To go backwards using segues, you need to use an unwind segue -- it's the only one that is an exception to the rule that segues always instantiate new controllers. The other ways to go backwards, without segues, are popping with navigation controllers, and dismissing modal controllers.
I can't really diagnose your immediate problem without a lot more information, but redesigning the storyboard using unwind segues would probably fix your problem.
This might be a very basic question, but I could not find the answer yet.
I have a UITableView that acts as a menu for my app. Each row on the table view, when selected, opens a different subclass of UIViewController.
At the moment my code works the same way used in the UICatlog example from Apple.
In the main view controller (the table view), each menu item is described in a dictionary in an array (menuList). Each dictionary contains an instance of the UIViewController subclass for that screen and other data about the menu item. When the user selects a row, the didSelectRow atIndexPath kicks in and calls the appropriate view controller, stored in the dictionary at that indexPath.row of the menuList array.
It seems to be very wasteful to alloc and init every single view controller when the table view first loads.
My question is: Is there a better way than the one demonstrated in UICatalog to alloc/init my view controller sublasses only when the associated row is tapped?
(I know I can use a complex if..else structure in the didSelectRow, but this results in an extremely long didSelectRow method and breaks encapsulation. I wonder if there is a cleaner way to do this, allocing and initing the appropriate view controller based on data from the dictionaries)
user1349768 try to use Storyboard, but this feature only works in iOs 4 and higher.
Just a suggestion ... put some reference to each view controller into NSArray and then initiate and segue to them when the row gets tapped on (and just get the reference from objectAtIndex:).
Although I could not find a better way to do this, the memory signature of each allocated View Controller is only 288 bytes. Since the solution suggested by apple is a lot more elegant and scalable then using a switch case statement, I left it as it is.
I have two table views and a detail view being managed by a UINavigationController. When a row is selected on the second table, it pops to a detailed view allowing changes specific data represented by the row. I need to be able to switch between the UITableView and the UIViewController without losing any of the data that might have been changed in the UIViewControllers (button selections, text values entered in fields, etc).
Basically, once the UIViewController is presented, one should be able to switch back and forth between the table and detail view without losing any data.
The problem is, when a UIViewController is popped from the navigation controller, that memory is automatically released, and since I'm using ARC, I can't just keep a pointer to that with a retain command in the UITableView.
I know that I could manually rebuild the view each time its corresponding table row is selected, but I feel that might be a messy solution. Another option I've thought of is keeping an array of pushed UIViewControllers and checking if the selected table row corresponds with an existing value before a new one is created, but that might also get messy.
Any suggestions?
Your final wish in this back and forth of view is what you stated in your question: you want to switch between view controllers without losing any information of the actions performed in these controllers.
But if you think at how MVC pattern works, you should consider a view controller as the glue logic between the view and the model. The view is not persistent, that's why it is legitimate for ARC to get rid of the owning view controller when the view is no more needed. Instead what you should persist while your app is working is the model data only: the model data will be shared between the involved view controllers, the view controllers will be recreated each time and the corresponding views will be updated based on the model data. The only reason why the view controller should be kept alive is when its alloc-init-loadView takes too much (e.g.: the view is OpenGL backed) but in such case I would suggest you to keep a strong reference to it in the AppDelegate and ask it to refresh the content when the model data is replaced.
So basically what you should do is:
- select the table
- extract the model data associated to the table, including all information relevant for the view controller
- push the view controller; save all view modifications to the model
- when the view controller is popped, the model data will be returned only
- next time, when you push the view controller again, you will restore the model and re-init the view controller.
This approach is not complicated and gives you the possibility to structure the app in a clean way. Tomorrow you can change your view controller structure (that its view and the logic) without any impact in the communication with the other view controllers as this managed by the model passing only.
There are a couple of solutions to this, just like you suggested.
The array solution is highly inefficient because of memory issues.
The second solution you proposed is a lot more elegant. Just write your own init method in that view controller and init the view controller with data from a plist file
If I'm reading the question correctly, you've got a tableView and a detailView that are driven by the same model data. When changes to the model data are made in the detail view, you want those changes to persist.
If you update the model based on the state of the controls when the detail view is popped, then those changes will persist and the changes will be visible the next time you drill back down into the detail view.
You don't mention what form the table data takes, but let's assume it's an NSArray of NSMutableDictionaries. When you tap the row, the didSelectRowAtIndexPath: method will need to hand the dictionary from that array index to the detail view controller through a property on the detail controller. The detail view controller will update the dictionary values in the method that dismisses it.
The way to think of this is using the model-view-controller pattern. The table and detail view data is stored in the model; the views present the data; and the controllers are responsible for updating the model and navigating between views.
Essentially I have a view controller where the user picks from three choices. Once the user chooses something, the view segues away to another view controller that displays some information regarding their choice for about 5 seconds and then segues back to original view controller automatically where the User must make more choices... (its basically a loop until something is accomplished).
The problem I am having is when the User touches their option, it seems to just segue back to itself without ever displaying the intermediary screen. I added a sleep(5); to the viewDidLoad but all that causes it to do is pause on the original choice screen for 5 seconds before segueing to itself. I also put in an NSLog in just to make sure it was actually using the new controller, which it is indeed.
I didn't include code since its so trivial. viewDidLoad on the new controller, has sleep(5) and the call to segue back to the original view controller.
I solved the problem by moving the code to viewDidAppear. Should have done that from the beginning honestly, just didn't think it through enough I guess.
Quite possibly I'm missing something obvious, but I have a very simple requirement and neither of these two seems to meet it.
I have an application with 3 distinct views, however for reasons I won't go into here (essentially views may or may not be valid depending in what is done in other views), using persistant tabs as navigation will not work. I also want each view to be created as needed and UITabBarController creates all its views upfront. However I still want some of the functionality of UITabBarController - being able to pass it in an Array of UIViewControllers.
UINavigationController offers the chance to have it create its views as needed, but there is no way for me to pass a list of views to it up front, so I end up with ViewControllers creating and pushing other (sibling) ViewControllers which is nasty.
So here are my requirements:
I want to be able to add ViewControllers upfront
I want to be able to navigate between the view controllers
I want each ViewController to be created as needed and destroyed when navigated away from
Is there anything that fits the bill?
I would use the AppDelegate to create a hash of viewcontrollers upfront and create a navigation controller.
Once you click the button to navigate to a new viewcontroller you can go to the hash and look for that specific view controller. If it is not created you can create it there. If you want to destroy that view controller just release it and remove from the hash.