I understand that with my page control I can get the current view controller with "pageControl.currentPage".
Let's say I have a total of 3 view controllers, but the second view controller is being re-used.
So the order is [1stViewController, 2ndViewController, 2ndViewController]
From 2ndViewController, how can I determine if it's the 1st or 2nd index in the order?
I would like to be able to check in the viewDidLoad method before I update the UI of the view controller.
Check out this little project I threw together:
https://github.com/PJayRushton/PageViewControllerReferences
Basically I just created an array of view controllers used in the PageViewController DataSource and in the reused ViewController I check which view controller from the stored array it is.
Related
I'm using a Master Detail View Controller with Swift.
When I click on a master cell, I see a collection view containing a list of pictures.
Each picture represent data stored inside Core Data.
Each picture data has also a timestamp and all picture taken the same day are stored in the same Master cell.
[Date of the day 1]
[pic1]
[pic2]
[Date of the day 2]
[pic3]
[pic4]
What I want to achieve is:
When I click on a picture, another ViewController is displayed (through a segue) and this new VC allows me to edit the picture and change its date.
The thing is I have multiple things happening here when I change the day or a picture:
if the pic was alone in the collection, then I also have to remove the Master Day cell too.
if the pic was not alone, I just need to update the detail collection view
In any cases, if I have to create a new Day, I need to create a new Master Cell and update the view and if I need to delete a Day, I have to also update the Master view.
If you edit the collection items, you can simply do a:
self.collectionView performBatchUpdates:
and then update the model, and notify the collection view of your action...
but I don't see how I can do that from another UIViewController.
Currently, in the Edit View Controller, I update the model and then dismiss the View controller. And I get a crash because the collectionView tries to display an Item that is not part of the current collection anymore...
To solve this issue, maybe I can use a protocol in order to inform the detail view from the edit view but If I do that, I need to give the IndexPath of the Edit Cell to the edit view and then give it back to the detail view through the protocol... Why not. but not that clean in my opinion.
Another problem is, the app seems to also crash in the master view when I delete a Day. Because, the master view doesn't know that I deleted a day from the edit view.
My main problem is that I don't see how to tell my Master View Controller that I made some model changes... especially when I don't have any IndexPath information from within the edit view.
Technically, I could use the notificationCenter to notify both Views, I guess... but still, I would need to pass both IndexPath from the Master view to the Detail view and then to the Edit view.
Ugly.
Several ways by which this can be achieved:
1) Delegation: The view controller containing collection view will act as a delegate of Edit View Controller and when editing is done it will callback a method to 'The view controller containing collection view'
2) Notification: EditingFinished
3) blocks
Using protocol is good solution but can be painful since you have to manage edited items using their indexPaths. A simpler solution, since you are using CoreData, is to fetch entries using a computed property and just call collectionView.reloadData() on viewWillAppear method from the controller that contains collectionView. This way calling reload data will recompute Core Data entries and will place each item in correct position. Also viewWillAppear will get called after dismissing controller that stands on top of collection view controller
I found an interesting article addressing my problem.
It was not indeed a trivial problem...
http://www.objc.io/issues/4-core-data/full-core-data-application/#using-a-collection-view
I am implementing a scroll style page view controller for my app, based on the page based application template.
In the data source class, I am storing the list of view controllers in a dictionary (could also use array I guess) so that I can reuse them if the user swipes back to a view controller they already viewed. There are about 15 total view controllers in the page view controller.
I wonder if this is a good idea compared to calling the story board instantiateViewControllerWithIdentifier each time. (I understand the pageviewcontroller itself stores its own array of view controllers anyway.)
I could instead just store the model object in the dictionary or array and instantiate the view controller and pass in the model object after calling instantiateViewControllerWithIdentifier.
I am interested in what is likely to be the better approach.
I have a basic modal view system.
My app loads the UI base in which there are 2 buttons presenting 2 other views.
In those views, a dismiss button.
Everything works fine.
BUT, in one of the 2 modal views, I have a bunch of UISlider & UISwitch.
I want them to retain their values but the dismiss loses them: as soon as I trigger the button to show the view containing the UI elements, this view is shown with all values for all elements as I put initially in the xib.
should I store all values in variables, then in viewWillAppear I could "recall" them ?
would you advice me another strategy ?
Yes, your proposed approach is exactly the right sort of thing. But be careful; viewWillAppear can be called for many reasons; make sure you're only doing this when the view controller is coming into existence and showing the view for the first time.
NSUserDefaults can be an excellent place to store globally needed info like this. In viewWillDisappear, store the desired state info (values of the sliders and switches) in defaults. Then retrieve them the next time the view is about to appear.
When you create the modal view you are creating a new instance of the modalViewController an the modalView. This new instance knows nothing about any other instance. There are a few ways you can retain the information from previous iterations of these modal view controllers.
How I would do it:
Set up place holders in your main view and pass the values that the user selects back to the main view via a protocol and delegate setup. Then when you segue to the modal view you can load those variables in before displaying the modal view.
So let's say you have a dictionary with all of the values: {slider = YES, someValue=10,...} Create that dictionary in the main view controller, the first one that opens, and place some default values in it.
In your modal view controllers create the same dictionary as a property.
Create a protocol in your modal view controller with a method that is something like
- (void) doneEditing:(NSDictionary *)values
Set up your first view as the delegate for the modal view controller and in the implementation of doneEditing copy the values to the dictionary that is present in the first view before popping the modal view.
When the first view is ready to present the modal view again, copy the values to the dictionary property of the modal view before presenting it.
I hope this gets you headed in the right direction. It's important to remember that each time you segue or create and present a modal view you are creating a brand new instance of that view, it knows nothing about the previous instance at all unless you tell it something about it.
My root view is a grouped tableview. When the user selects a row, i want to be able to retain which row was selected to give to the detailcontroller for loading the correct data.
All the navigation is working fine, I just don't want to have to create a global variable to just retain the index. Is there a built in method for the navcontroller or something?
You can either set a property in you detail view controller before it is pushed giving info about the row selected so it can influence the behaviour of the detail view controller, or it is possible to access the parent view controller directly from the detail view controller with:
#property(nonatomic, readonly) UIViewController *parentViewController
I prefer the first option - you can write a custom init... method, to supply the data for the detail view controller when it's created.
There isn't a builtin way as such, you should try and make the view controllers de-coupled as possible so they can be re-used and are resistent to changes elsewhere in the app.
This is a useful quote from the View Controller Programming Guide for iOS:
With the exception of view controllers managing leaf data, each custom view controller must provide a way for the user to navigate to the next level of the data hierarchy. A view controller that displays a list of items can use taps in a given table cell to display the next level of data. For example, when a user selects a photo album from the top-level list, the Photos application creates a new photo album view controller. The new view controller is initialized with enough information about the album for it to present the relevant photos.
I wanted to follow up with how I ended up coding this. I'm still somewhat new to Obj-C, so some concepts I haven't dealt with or come across, so if this is old hat, sorry.
You can create your data element in the child controller and pass the data 1 for 1 directly to that element by accessing its property.
ParentController.h
NSDictionary *myData;
ChildController.h
NSDictionary *childData;
// This would get called in the parent controller where appropriate
// but before the child controller is presented
ChildController.childData = myData;
This is obviously very stripped down, but the idea works. Just take your data and pass it to the property before calling it and it will be there once the child view is presented. Hope this helps.
I'd like to understand what's going on here. Basically I have a NumberOneViewController which owns a table view and is showing up on the details view controller on a split view based app.
When a user selects an entry on the NumberOneViewController tableview row, i assign the table view to RootViewController's tableView member like so:
self.tableView = numberOneViewController.tableView;
So the table view on the detail view controller is now gone - which brings me to my first question, what exactly happened here?
Now, I want number one view controller's table view again to show up on the details view controller, but how?
Maybe you need to reload/refresh the table view after you assign it. Just throwing out something off the top off my head since there are no other answers. Good Luck.