I am working on an application where I need to pass an array of values from a click of tableview cell in my tableviewcontroller which is the initial view controller to a contentview view controller with page curl transition.
Each of the page will have a textview which will be populated with value passed from the initial view controller and can be edited by the user.
My issue is, I am not able to update the array with the new value and pass it back to the initial view controller
I tried the following:
I implemented pageviewcontroller methods in my initialview controller to create instances of the ContentViewController with page curl transition and was able to pass values to each of the pages when the page curl was done. But I am trying to figure out a way to pass back the updated value to the tableviewcontroller from where I instantiated the object.
I tried Segue from tableview to the contentViewcontroller, but it does not work.
Appreciate if somebody can help me.
Use the delegate pattern.
Define a protocol within ContentViewController :
protocol UpdateModelDelegate {
func didDismissContentViewController(controller:ContentViewController)
}
Establish a delegate variable within ContentViewController :
var delegate: UpdateModelDelegate?
When you dismiss ContentViewController call delegate?.didDismissContentViewController(self) which will send the data back to your UITableViewController.
Have the UITableViewController conform to this protocol.
class MyTableViewControllerSubclass: UITableviewController, UpdateModelDelegate
When presenting the ContentViewController set your UITableViewSubclass as the delegate.
override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
var contentViewController: ContentViewController()
//After you pass the necessary data to contentViewController...
contentViewController.delegate? = self
}
finally, implement the delegate function within your UITableviewController subclass.
func didDismissContentViewController(controller:ContentViewController) {
//You're passed in the contentViewController here, use relevant data to update your model.
}
Related
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."
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.
I am neither an iOS developer, nor a swift developer, but please bear with me:
I am currently trying to implement a simple iOS app but I have difficulties understanding how exactly I am supposed to set up custom UIViews and ViewControllers for those UIViews.
I am using a UIScrollView that is containing items a little bit more complex than just images, thats what I use custom views for.
What I did was:
I created a .xib file, the view itself. I added some elements (here it is only a textfield, for simplicity's sake).
I created a cocoa touch class "CustomView" that inherits from UIView and set my view up to be of that class (inside the class I just set up elements and such).
Now I want a ViewController that controls the class whenever it is rendered (for example reacting to the changing textField).
I cant manage everything from my main ViewController, because it would get too big (e.g. 3 scrollViews * 5 subviews that need to be managed).
I want a solution that uses ViewControllers for each subview (in case they themselves will have subviews, too).
How do I do that?
Do I need to add some sort of childViewController?
I really am at loss, most of the blog posts and SO examples simply do not work and/or are outdated and I am unsure about whether or not I got the whole View - ViewController pattern wrong.
Let's say you have two view controllers, MainViewController and TableViewController. TableVC's main view is to be a subview of MainVC's main view. In addition, you wish to pass back to MainVC which cell was selected in TableVC.
A solution is (a) make TableVC be a child to MainVC and (b) make MainVC be a delegate for TableVC.
TableViewController:
protocol TableVCDelegate {
func cellSelected(sender: TableViewController)
}
class TableViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
// please note that you can do delegation differently,
// this way results in crashes if delegate is nil!
var delegate:TableVCDelegate! = nil
var someValue = ""
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
// set someValue to contents in the selected cell or it's data source
someValue = "Hello World!"
delegate.cellSelected(sender: self)
}
}
MainViewController:
class MainViewController: UIViewController, TableVCDelegate {
let tableVC = TableViewController()
override func viewDidLoad() {
// make tableVC be a child of this VC
addChild(tableVC)
tableVC.didMove(toParent: self)
tableVC.delegate = self
// position tableVC.view
tableVC.view.translatesAutoresizingMaskIntoConstraints = false
}
func cellSelected(sender: TableViewController) {
print(sender.someValue) // this should send "Hello World!" to the console
}
}
This is obviously untested code, but it is based on product code. This is meant to be a shell to help you get started.
In VC#1, I have a UITableView. When I tap on a cell, I am brought to VC#2 where information about that cell is displayed.
I want to be able to press a button in VC#2 which changes the title of the cell it corresponds with in VC#1, but I am confused on how to do this?
Should I create a variable in VC#2 to save the indexPath for the cell that was tapped, and then call a function in VC#1 from VC#2 that uses that indexPath to update the cell? If I did this, wouldn't VC#1 need to be static so I know I'm modifying the right instance of VC#1? I'm using a push segue and a navigation controller to go back, so creating a new instance of VC#1 wouldn't reference the same VC im trying to modify as I believe?
Is there an easier way to do this?
You should use the delegate pattern.
VC1 should know what cell that VC2 is showing. You should have an IndexPath property in VC1 that stores what cell is VC2 currently displaying, right?
Now, create a protocol called VC2Delegate:
protocol VC2Delegate : class {
func titleDidChange(_ vc2: VC2, to title: String)
}
Now, add this property in VC2:
weak var delegate: VC2Delegate?
Now, when you think the title of the cell should change, call the delegate:
delegate?.titleDidChange(self, to: "Some Title")
That's all for VC2.
Make VC1 conform to VC2Delegate:
extension VC1: VC2Delegate {
func titleDidChange(_ vc2: VC2, to title: String) {
// set the text of the table cell here...
}
}
Now, when you are passing data to VC2 from VC1, probably in the prepareForSegue method, do
vc2.delegate = self
Learn more about delegates here.
You can pass every data you want through view controllers using delegates
First create a protocol whatever you want
protocol ViewControllerDelegate {
func getSelected(value:Int)
}
Create a variable from your ViewController you want pass the data
var delegate: ViewControllerDelegate?
On didSelectRowAt method you will do
if delegate != nil {
delegate.getSelected(value: indexPath.row)
}
self.navigationController?.popViewController(animated: true)
On ViewController that will receive data you have to do this
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let vc = segue.destination as? SecondViewController {
vc.delegate = self
}
}
extension YourViewController: ViewControllerDelegate {
fun getSelected(value:Int) {
// Get value from another view controller and manage it
}
}
This code is in Swift 4
If you don't understand something let me know
It's wrong approach you are pursuing. You must separate your data layer from your presentation layer. So in VC#2 you edit your visualized data, then VC#1 reloads the data to update its view.
Short answer: You should not do that at all.
View controllers should not modify other view controller's views.
You should modify the data model in VC2, then send a message back to VC1 telling it to update the cell.
(In the push segue you can set up VC1 to be VC2's delegate, then define a protocol that VC2 uses to notify VC1 about the indexPath's of the data model that need to be updated.)
Im new to programming and trying to build my own app, I wonder how Im I supposed to link the info I get from the addTask viewcontroller to the tableview cell? At the moment Im just trying to get the text from the textfield and Im going to add the other features later.
What Im trying to do
Refer This :-
Create a global array add remove element from that array on click of your button
You can pass data from one view controller to another using Delegates. Check my ans here. You can set your table view class as delegate of your task view controller. Implement the protocol methods of task view controller get the data and reload table.
Hope it helps.
Happyy Coding!!
You can pass data using Delegation .
In Second ViewController
import UIKit
protocol secondViewDelegate: class {
func passData(arrData : [Any])
}
class SecondViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
weak var delegate: secondViewDelegate? = nil
#IBAction func clickOnButton(_ sender: Any) {
self.delegate.passData([]) // replace your array here
}
}
In FirstViewController
class FirstViewController: UIViewController, UITableViewDataSource, secondViewDelegate
let objectSecondVC: SecondViewController? = storyboard?.instantiateViewController(withIdentifier: "secondVCID") as! SecondViewController?
objectSecondVC?.delegate = self
navigationController?.pushViewController(objectSecondVC?, animated: true)
Second ViewController Delegate Method in FirstViewController
func passData(arrData : [Any]){
// append to your main array
}
It seems like your add task view controller is connected with your table view controller though a segue. So when you moving back from add task view controller, you can use unwind to pass data back. Here is a detailed tutorial with simple instructions and pictures.
In a detail view controller, I've a 'featureImage' in the top left, and a thin horizontal strip of images below this. The strip of images is an embedded container view managed by a custom CollectionViewController, which shows an array of images. The initial featureImage is the first image in an array of images[0], and the same array is passed to the collection view.
I'd like the featureImage to update to the same image if a cell in the container view is selected / tapped.
I guess I need to call the delegate method didSelectItemAtIndexPath, which will give me the indexPath. Right? But then how do I pass the indexPath, which is already from a delegate, back to the detail view controller.
EDITED - The code shows code overlap and differences between Responder Chain AND delegate approaches. Uncommented in the didSelectItemAtIndex path, the Responder Chain approach works, while the delegate approach does not.
Protocol defined and included at top of DetailViewController (I doesn't seem to matter which file the protocol is in, and is only typed to class to allow the delegate property to be 'weak'). Needed for both approaches.
protocol FeatureImageController: class {
func featureImageSelected(indexPath: NSIndexPath)
}
class DetailViewController: UIViewController, FeatureImageController {
Delegate property declared in the custom UICollectionViewController class. Only needed for delegate approach.
weak var delegate: FeatureImageController?
Delegate property initiated in the DetailViewController. Only needed for delegate approach.
override func viewDidLoad() {
super.viewDidLoad()
let photoCollectionVC = PhotoCollectionVC()
photoCollectionVC.delegate = self as FeatureImageController ... }
The Responder Chain (active) OR the delegate approach (commented out) within the collection view controllers didSelectItemAtIndexPath method.
override func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath)
{
if let imageSelector = targetForAction("featureImageSelected:", withSender: self) as? FeatureImageController {
imageSelector.featureImageSelected(indexPath)
}
// self.delegate?.featureImageSelected(indexPath)
}
Delegate method in DetailViewController. Needed for both.
func featureImageSelected(indexPath: NSIndexPath) {
record?.featureImage = record?.images[indexPath.row]
self.configureView()
}
The communication of data selection between View Controllers in my experience can best be achieved in two ways- the delegation or responder chain route. Either way the first step would be creating a protocol that your DetailViewController will adhere to. Something like:
protocol FeatureImageController: class {
func featureImageSelected(image: UIImage)
}
Your DetailViewController would then implement this function and use it to change the 'feature image'. How this is communicated then depends on whether you use delegation or the responder chain.
Delegation
If you prefer to use delegation then declare a delegate property on your CollectionViewController like so:
weak var delegate: FeatureImageController?
then in didSelectItemAtIndexPath you would determine the selected image using the provided indexPath and pass it to your delegate:
delegate?.featureImageSelected(selectedImage)
where selectedImage is the image selected from the collection view.
Responder Chain
If you decide to use the responder chain then you need not declare a delegate property. Instead you would ask for the first target that responds to your protocol method. So inside didSelectItemAtIndexPath you would say:
if let imageController = targetForAction("featureImageSelected:", withSender: self) as? FeatureImageController {
imageController.featureImageSelected(selectedImage)
}
Both methods (delegation or responder chain) allow the collection view controller to pass its selection to the detail controller. The delegation route is more common in the Framework but I find as we use containers within containers more often it becomes pretty nasty to properly manage the chain of delegates without an amount of 'coupling' I'm not comfortable with. The responder chain, on the other hand, is already provided by the framework to 'dig' into the hierarchy of controllers to find one willing to handle your action.