App development

Drag and Drop Tutorial for iOS [FREE]

Apple launched drag and drop performance in iOS 11, permitting customers to pull objects from one display location to a different. On iPhone, drag and drop is simply obtainable inside an app, whereas on iPads, it’s additionally obtainable throughout apps. That is actually useful for doing issues like rapidly including photographs from Images into an electronic mail.

On this tutorial, you’ll discover drag and drop by constructing upon CacheManager, two apps for managing geocaches:

CacheMaker organizes geocaches in a Kanban board of in-progress and accomplished objects. CacheEditor permits customers to edit the main points of a geocache introduced over from CacheMaker. You’ll implement these administration options by including drag and drop assist to each apps.

Getting Began

Use the Obtain Supplies button on the prime or backside of this tutorial to obtain the starter venture. Open CacheManager.xcworkspace in Xcode and choose CacheMaker because the lively scheme:

Construct and run CacheMaker. You need to see two assortment views with the primary containing geocaches for in-progress work:

Attempt dragging a geocache from the in-progress lane to the finished lane:

Your purpose on this first a part of the tutorial is to get this working. In a while, you’ll unlock the power to pull and drop geocaches to and from the CacheEditor companion app.

Check out the important thing CacheMaker information in Xcode:

CachesDataSource.swift: Represents the information supply for a set view of geocaches.

CachesViewController.swift: Shows the Kanban board for the geocaches.

These are the information you’ll be working with so as to add the specified performance.

Drag and Drop Overview

While you drag objects from a supply app, a drag exercise begins and the system creates a drag session. The supply app units up a drag merchandise to signify the underlying information when the drag exercise begins. Dropping the objects in a vacation spot app ends the drag exercise.

Drag objects are wrapped in an merchandise supplier which describes the information varieties the supply app can ship. When the objects are dropped, the vacation spot app asks for the objects within the format it may well eat.

Apple robotically helps drag and drop in textual content views and textual content fields. It additionally gives specialised APIs for desk views and assortment views. You may add drag and drop to customized views as properly.

On this tutorial, you’ll discover drag and drop in assortment views and customized views.

Including Drag Assist

Go to CachesDataSource.swift and add the next extension to the tip of the file:

extension CachesDataSource

Right here you create an merchandise supplier from the NSString illustration of the geocache title. You then return an array of 1 drag merchandise which wraps this merchandise supplier.

Subsequent, open CachesViewController.swift and add the next to the tip of the file:

extension CachesViewController: UICollectionViewDragDelegate

You undertake UICollectionViewDragDelegate and implement the required methodology that’s referred to as when a drag exercise begins. Your implementation will get the information supply for the gathering view, then returns the corresponding drag objects for the chosen merchandise.

Add the next to viewDidLoad() after the gathering view delegate task:

collectionView.dragDelegate = self

This makes the view controller the drag delegate.

Construct and run the app. Faucet and maintain on a set view cell representing a geocache. The tapped cell ought to stand up permitting you to pull it round:

Word that though you possibly can drag an merchandise round, you possibly can’t drop it anyplace. Trying to take action merely drops it again the place it began.

Open Reminders in Break up View subsequent to CacheMaker. You need to have the ability to drag a geocache and drop it into Reminders:

Reminders can settle for the exported NSString illustration of the geocache title and use it to create a brand new reminder.

Now strive dragging any textual content from Reminders into CacheMaker. Nothing occurs. That’s since you haven’t added drop assist to CacheMaker. You’re going to sort out this subsequent.

Including Drop Assist

Go to CachesDataSource.swift and add the next to the CachesDataSource extension:

func addGeocache(_ newGeocache: Geocache, at index: Int)

This provides a brand new geocache to the information supply.

Change over to CachesViewController.swift and add the next protocol extension to the tip:

extension CachesViewController: UICollectionViewDropDelegate {
func collectionView(
_ collectionView: UICollectionView,
performDropWith coordinator: UICollectionViewDropCoordinator) {
// 1
let dataSource = dataSourceForCollectionView(collectionView)
// 2
let destinationIndexPath =
IndexPath(merchandise: collectionView.numberOfItems(inSection: zero), part: zero)
// three
let merchandise = coordinator.objects[0]
// four
change coordinator.proposal.operation

}
}

Right here you undertake the UICollectionViewDropDelegate protocol. You then implement the required methodology that’s referred to as when the consumer ends a drag exercise. Your implementation:

Will get the information supply for the gathering view.
Units the tip of the gathering view because the merchandise drop vacation spot.
Selects the primary drag merchandise.
Checks how you plan to deal with the drop.
Asynchronously fetches the dragged merchandise’s information.
Creates a brand new geocache with a reputation primarily based on the incoming string information.
Provides the brand new geocache to the information supply.
Inserts the brand new merchandise within the assortment view. You invoke this on the principle thread for the reason that information fetching completion block runs on an inside queue.

Responding to Drops

Add the next to the tip of the UICollectionViewDropDelegate extension:

func collectionView(
_ collectionView: UICollectionView,
dropSessionDidUpdate session: UIDropSession,
withDestinationIndexPath destinationIndexPath: IndexPath?
) -> UICollectionViewDropProposal

You specify the response to an merchandise being dragged. This consists of offering visible suggestions to the consumer.

The code right here forbids drag-and-drops inside the app. It proposes copy operations for objects dropped from one other app.

Add the next to viewDidLoad() after the drag delegate is assigned:

collectionView.dropDelegate = self

This units the view controller because the drop delegate.

Construct and run the app. With Reminders in Break up View, confirm that you may drag a reminder into the in-progress assortment view:

For those who attempt to drop into the center of the checklist, you’ll see it solely provides to the tip of the checklist. You’ll enhance this later.

Attempt dragging and dropping a geocache contained in the app. Confirm that you just get a visible cue that that is disallowed:

That isn’t superb, so that you’ll work on it subsequent.

Drag and Drop within the Identical App

Nonetheless in CachesViewController.swift, go to collectionView(_:dropSessionDidUpdate:withDestinationIndexPath:) and change the forbidden return assertion with this code:

guard session.objects.depend == 1 else
return UICollectionViewDropProposal(operation: .cancel)

if collectionView.hasActiveDrag else

If a couple of merchandise is chosen, the code cancels the drop. For the only drop merchandise you plan a transfer for those who’re inside the similar assortment view. In any other case, you plan a replica.

In CachesDataSource.swift, add the next methodology to the extension:

func moveGeocache(at sourceIndex: Int, to destinationIndex: Int)

This repositions a geocache within the information supply.

Head again to CachesViewController.swift and in collectionView(_:performDropWith:) change the destinationIndexPath task with the next:

let destinationIndexPath: IndexPath
if let indexPath = coordinator.destinationIndexPath
destinationIndexPath = indexPath
else

Right here, you verify for an index path specifying the place to insert the merchandise. If none is discovered, the merchandise inserts on the finish of the gathering view.

Add the next proper earlier than the .copy case:

case .transfer:
print(“Shifting…”)
// 1
if let sourceIndexPath = merchandise.sourceIndexPath

This block of code:

Will get the supply index path which it is best to have entry to for drag and drops inside the similar assortment view.
Performs batch updates to maneuver the geocache within the information supply and assortment view.
Animates the insertion of the dragged geocache within the assortment view.

Comply with My Strikes

Construct and run the app. Confirm that dragging and dropping a geocache throughout assortment views creates a replica and logs the copy message:

Take a look at that you may additionally transfer a geocache inside the similar assortment view and see the transfer message logged:

You might need seen some inefficiencies when dragging and dropping throughout assortment views. You’re working in the identical app but you’re making a low constancy copy of the thing. To not point out, you’re creating a replica!

Absolutely, you are able to do higher.

Optimizing the Drop Expertise

You may make just a few optimizations to enhance the drop implementation and expertise.

Utilizing In-Reminiscence Knowledge

You need to benefit from your entry to the total geocache construction in the identical app.

Go to CachesDataSource.swift. Add the next to dragItems(for:), instantly earlier than the return assertion:

dragItem.localObject = geocache

You assign the geocache to the drag merchandise property. This permits sooner merchandise retrieval later.

Go to CachesViewController.swift. In collectionView(_:performDropWith:), change the code contained in the .copy case with the next:

if let geocache = merchandise.dragItem.localObject as? Geocache else

Right here, the code that handles objects dropped from a special app hasn’t modified. For objects copied from the identical app, you get the saved geocache from localObject and use it to create a brand new geocache.

Construct and run the app. Confirm that dragging and dropping throughout collections views now replicates the geocache construction:

Shifting Gadgets Throughout Assortment Views

You now have a greater illustration of the geocache. That’s nice, however you actually ought to transfer the geocache throughout assortment views as an alternative of copying it.

Nonetheless in CachesViewController.swift, change the collectionView(_:dropSessionDidUpdate:withDestinationIndexPath:) implementation with the next:

guard session.localDragSession != nil else
guard session.objects.depend == 1 else
return UICollectionViewDropProposal(operation: .cancel)

return UICollectionViewDropProposal(
operation: .transfer,
intent: .insertAtDestinationIndexPath)

You now deal with drops inside the similar app as transfer operations.

Go to File ▸ New ▸ File… and select the iOS ▸ Supply ▸ Swift File template. Click on Subsequent. Title the file CacheDragCoordinator.swift and click on Create.

Add the next on the finish of the file:

class CacheDragCoordinator

You’ve created a category to coordinate drag-and-drops inside the similar app. Right here you arrange properties to trace:

The place the drag begins.
When it’s accomplished.
If the gathering view objects ought to be reordered after the drop.

 

Change to CachesDataSource.swift and add the next methodology to the extension:

func deleteGeocache(at index: Int)

This methodology removes a geocache on the specified index. You’ll use this helper methodology when reordering assortment view objects.

Go to CachesViewController.swift. Add the next to collectionView(_:itemsForBeginning:at), instantly earlier than the return assertion:

let dragCoordinator = CacheDragCoordinator(sourceIndexPath: indexPath)
session.localContext = dragCoordinator

Right here, you initialize a drag coordinator with the beginning index path. You then add this object to the drag session property that shops customized information. This information is simply seen to apps the place the drag exercise begins.

Are You My App?

Discover collectionView(_:performDropWith:). Exchange the code contained in the .copy case with the next:

print(“Copying from completely different app…”)
let itemProvider = merchandise.dragItem.itemProvider
itemProvider.loadObject(ofClass: NSString.self) string, error in
if let string = string as? String
let geocache = Geocache(
title: string, abstract: “Unknown”, latitude: zero.zero, longitude: zero.zero)
dataSource.addGeocache(geocache, at: destinationIndexPath.merchandise)
DispatchQueue.predominant.async
collectionView.insertItems(at: [destinationIndexPath])

You’ve simplified the copy path to solely deal with drops from a special app.

Exchange the code contained in the .transfer case with the next:

// 1
guard let dragCoordinator =
coordinator.session.localDragSession?.localContext as? CacheDragCoordinator
else return
// 2
if let sourceIndexPath = merchandise.sourceIndexPath
print(“Shifting inside the similar assortment view…”)
// three
dragCoordinator.isReordering = true
// four
collectionView.performBatchUpdates(
dataSource.moveGeocache(at: sourceIndexPath.merchandise, to: destinationIndexPath.merchandise)
collectionView.deleteItems(at: [sourceIndexPath])
collectionView.insertItems(at: [destinationIndexPath])
)
else
// 7
dragCoordinator.dragCompleted = true
// eight
coordinator.drop(merchandise.dragItem, toItemAt: destinationIndexPath)

Right here’s a step-by-step breakdown of the what’s occurring:

Get the drag coordinator.
Verify if the supply index path for the drag merchandise is ready. This implies the drag and drop is in the identical assortment view.
Inform the drag coordinator that the gathering view shall be reordered.
Carry out batch updates to maneuver the geocache within the information supply and within the assortment view.
Word that the gathering view just isn’t going to be reordered.
Retrieve the domestically saved geocache. Add it to the information supply and insert it into the gathering view.
Let the drag coordinator know that the drag completed.
Animate the insertion of the dragged geocache within the assortment view.

Add the next methodology to your UICollectionViewDragDelegate extension:

func collectionView(_ collectionView: UICollectionView,
dragSessionDidEnd session: UIDragSession)

This methodology is named when both the drag is aborted or the merchandise is dropped. Right here’s what the code does:

Verify the drag coordinator. If the drop is full and the gathering view isn’t being reordered, it proceeds.
Get the information supply and supply index path to organize for the updates.
Carry out batch updates to delete the geocache from the information supply and the gathering view. Recall that you just beforehand added the identical geocache to the drop vacation spot. This takes care of eradicating it from the drag supply.

Construct and run the app. Confirm that shifting throughout assortment views really strikes the merchandise and prints Shifting between assortment views… within the console:

Including a Placeholder

Fetching objects from an exterior app and loading them within the vacation spot app may take time. It’s good apply to supply visible suggestions to the consumer comparable to exhibiting a placeholder.

Exchange the .copy case in collectionView(_:performDropWith:) with the next:

print(“Copying from completely different app…”)
// 1
let placeholder = UICollectionViewDropPlaceholder(
insertionIndexPath: destinationIndexPath, reuseIdentifier: “CacheCell”)
// 2
placeholder.cellUpdateHandler =
// three
let context = coordinator.drop(merchandise.dragItem, to: placeholder)
let itemProvider = merchandise.dragItem.itemProvider
itemProvider.loadObject(ofClass: NSString.self) { string, error in
if let string = string as? String
}

That is what’s occurring:

Create a placeholder cell for the brand new content material.
Outline the block that configures the placeholder cell.
Insert the placeholder into the gathering view.
Commit the insertion to trade the placeholder with the ultimate cell.

Construct and run the app. Drag and drop an merchandise from Reminders. Word the transient look of the placeholder textual content as you drop the merchandise into a set view:

A number of Knowledge Representations

You may configure the varieties of information that you may ship to a vacation spot app or eat from a supply app.

While you create an merchandise supplier utilizing init(object:), the thing you cross in should conform to NSItemProviderWriting. Adopting the protocol consists of specifying the uniform kind identifiers (UTIs) for the information you possibly can export and dealing with the export for every information illustration.

For instance, you might need to export a string illustration of your geocache for apps that solely absorb strings. Otherwise you would possibly need to export a picture illustration for photograph apps. For apps underneath your management that use geocaches, you might need to export the total information mannequin.

To correctly eat dropped objects and switch them into geocaches, your information mannequin ought to undertake NSItemProviderReading. You then implement protocol strategies to specify which information representations you possibly can eat. You’ll additionally implement them to specify the best way to coerce the incoming information primarily based on what the supply app sends.

To this point, you’ve labored with strings when dragging and dropping geocaches between apps. NSString robotically helps NSItemProviderWriting and NSItemProviderReading so that you didn’t have to write down any particular code.

To deal with a number of information varieties, you’ll change the geocache information mannequin. You’ll discover this within the Geocache venture, which is a part of the Xcode workspace you might have open..

Within the Geocache venture, open Geocache.swift and add the next after the Basis import:

import MobileCoreServices

You want this framework to make use of predefined UTIs comparable to these representing PNGs.

Add the next proper after your final import:

public let geocacheTypeId = “com.razeware.geocache”

You create a customized string identifier that can signify a geocache.

Studying and Writing Geocaches

Add the next extension to the tip of the file:

extension Geocache: NSItemProviderWriting {
// 1
public static var writableTypeIdentifiersForItemProvider: [String]
// 2
public func loadData(
withTypeIdentifier typeIdentifier: String,
forItemProviderCompletionHandler completionHandler:
@escaping (Knowledge?, Error?) -> Void)
-> Progress?
}

Right here you conform to NSItemProviderWriting and do the next:

Specify the information representations you possibly can ship to the vacation spot app. You need to return a string array ordered from the best constancy model of the thing to the bottom.
Implement the tactic for delivering information to the vacation spot app when requested. The system calls this when an merchandise is dropped and passes within the acceptable kind identifier.
Return the geocache’s picture within the completion handler if a PNG identifier is handed in.
Return the geocache’s title within the completion handler if a textual content identifier is handed in.
If the customized geocache kind identifier is handed in, return a knowledge object akin to the complete geocache.

Now, add the next enum proper after geocacheTypeId is assigned:

enum EncodingError: Error
case invalidData

You’ll use this to return an error code when there are issues studying in information.

Subsequent, add the next to the tip of the file:

extension Geocache: NSItemProviderReading {
// 1
public static var readableTypeIdentifiersForItemProvider: [String]
// 2
public static func object(withItemProviderData information: Knowledge,
typeIdentifier: String) throws -> Self
if typeIdentifier == kUTTypePlainText as String
// three
guard let title = String(information: information, encoding: .utf8) else
throw EncodingError.invalidData

return self.init(
title: title,
abstract: “Unknown”,
latitude: zero.zero,
longitude: zero.zero)
else if typeIdentifier == geocacheTypeId else
throw EncodingError.invalidData

}

Right here you conform to NSItemProviderReading to specify the best way to deal with incoming information. That is what’s occurring:

Specify the varieties of incoming information the mannequin can eat. The UTIs listed right here signify a geocache and textual content.
Implement the required protocol methodology for importing information given a sort identifier.
For a textual content identifier, create a brand new geocache with the title primarily based on the incoming textual content and placeholder info.
For the geocache identifier, decode the incoming information and use it to create a full geocache mannequin.

Errors or unrecognized kind identifiers throw the error you outlined earlier than.

Again to My App

Change the lively scheme to Geocache and construct the venture. Then change the lively scheme again to CacheMaker.

In CacheMaker, go to CachesDataSource.swift and inside dragItems(for:) change the itemProvider task to:

let itemProvider = NSItemProvider(object: geocache)

Right here you possibly can initialize your merchandise supplier with a geocache since your mannequin adopts NSItemProviderWriting to correctly export information.

Open CachesViewController.swift and discover collectionView(_:performDropWith:). Within the .copy case, change the merchandise supplier’s loadObject name with the next:

itemProvider.loadObject(ofClass: Geocache.self) { geocache, _ in
if let geocache = geocache as? Geocache
}

You’ve modified the drop handler to load objects of kind Geocache. The completion block now returns a geocache that you should use instantly.

Construct and run the app. Place Reminders in Break up View if obligatory. Verify that dragging and dropping objects between Reminders and CacheMaker works as earlier than:

Carry Images in Break up View to interchange Reminders. Drag a geocache out of your in-progress lane and drop it into Images to confirm that you may export a picture illustration of the geocache:

You may check the total information mannequin export path with a brief hack. Go to CachesViewController.swift and in collectionView(_:dropSessionDidUpdate:withDestinationIndexPath:) change the road that returns the transfer operation with the next:

return UICollectionViewDropProposal(
operation: .copy,
intent: .insertAtDestinationIndexPath)

You’re configuring drag-and-drops inside the similar app as copy operations. This triggers the code that ought to export and import the total information mannequin.

Construct and run the app. Take a look at that shifting an merchandise inside the app makes a correct copy of the geocache:

Revert your short-term hack in collectionView(_:dropSessionDidUpdate:withDestinationIndexPath:) in order that in-app drag-and-drops executes a transfer operation:

return UICollectionViewDropProposal(
operation: .transfer,
intent: .insertAtDestinationIndexPath)

Construct and run the app to get again to pre-hack situations.

Including Drag Assist to a Customized View

You’ve seen the best way to add drag and drop assist to assortment views. Including this assist to desk views follows an analogous course of.

You can too add drag and drop performance to customized views. The essential steps contain:

Including an interplay object to the customized view.
Implementing the protocol strategies within the interplay delegate to supply or to eat information.

It’s time to introduce CacheEditor, your companion app for enhancing geocaches. Change the lively scheme to CacheEditor. Construct and run the app then rotate the system to panorama mode:

View CacheMaker in Break up View, inserting it to the left of CacheEditor. Resize the Break up View so each apps take up about half the width:

Attempt dragging a geocache from CacheEditor into CacheMaker. You’re in for a irritating expertise, my pal.

You’ll be working with one key file in CacheEditor, CacheDetailViewController.swift, which shows geocache particulars. Open that file and add the next code to the tip:

// MARK: – UIDragInteractionDelegate
extension CacheDetailViewController: UIDragInteractionDelegate
func dragInteraction(
_ interplay: UIDragInteraction,
itemsForBeginning session: UIDragSession)
-> [UIDragItem]

Right here, you undertake UIDragInteractionDelegate and implement the tactic that’s referred to as when a drag exercise begins. The code ought to look just like what you’ve seen in CacheMaker. You come drag objects with a geocache because the merchandise supplier.

Add the next to viewDidLoad() proper after the decision to tremendous:

view.addInteraction(UIDragInteraction(delegate: self))

Right here, you create a drag interplay with the view controller because the delegate. You then add the interplay to the view.

Construct and run CacheEditor. Confirm that you may now drag a geocache from CacheEditor and drop it into CacheMaker:

Attempt dragging a geocache from CacheMaker into CacheEditor. Whereas the drag begins, it doesn’t drop. That’s your subsequent mission.

Including Drop Assist to a Customized View

Nonetheless in CacheDetailViewController.swift, add the next to the tip of the file:

// MARK: – UIDropInteractionDelegate
extension CacheDetailViewController : UIDropInteractionDelegate

Right here, you undertake UIDropInteractionDelegate and implement the elective strategies to trace and correctly deal with drops.

The primary methodology restricts drops to apps that cross in a Geocache object.

The second methodology returns a replica operation because the proposed methodology to deal with drops. This methodology is named when the consumer drags an merchandise over the drop interplay’s view. Although this protocol methodology is elective, that you must implement it to simply accept drops.

The final protocol methodology is named when the drop gesture is accomplished. You seize the merchandise supplier from the session and begin the information fetch. Then, you load within the first geocache and replace the view.

Subsequent, add this code to viewDidLoad() after the drag interplay setup:

view.addInteraction(UIDropInteraction(delegate: self))

With this, you create a drop interplay and set the view controller because the delegate. You then add the interplay to the view.

Construct and run the app. Confirm that you may drop a geocache into CacheEditor:

With only a few traces of code, you’ve added drag and drop assist to a customized view.

The place to Go From Right here?

Congratulations! You’ve used drag and drop to make the geocache administration pattern apps useful.

Use the Obtain Supplies button on the prime or backside of this tutorial to obtain the ultimate venture.

You need to now have the ability to add drag and drop to supercharge many in-app and cross-app experiences. Take a look at the Drag and Drop in Desk and Assortment Views and Drag and Drop with A number of Knowledge Representations and Customized Views video tutorials for extra suggestions and to see the best way to add this performance to desk views.

I hope you loved this tutorial. In case you have any feedback or questions, please be a part of the discussion board dialogue beneath!

asubhan
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