Xamarin: UICollection Image reorder Issue - ios

Question

I am using UICollectionView to store images and I can reorder them by overriding CanMove And MoveItem.
But the items inside the UICollection only reorder when cell size is large like if cell size is around 106 height and width, then they can be reordered if they are smaller in size, they are cannot be reordered.
View:
public override void ViewDidLoad()
{
base.ViewDidLoad();
//ImageCv is the name of UiCollectionView
var collectionLayout = new PostImageFlowLayout(3, 0.85f);
var allCollectionSource = new PostImageColectionSource(ImageCv, (ViewModel as NewPostDetailViewModel));
ImageCv.RegisterNibForCell(PostImageCell.Nib, PostImageCell.Key);
ImageCv.RegisterClassForSupplementaryView(typeof(CollectionHeader), UICollectionElementKindSection.Header, new NSString("headerId"));
ImageCv.BackgroundColor = UIColor.Clear;
ImageCv.Hidden = false;
ImageCv.DataSource = allCollectionSource;
ImageCv.Delegate = collectionLayout;
var longPressGesture = new UILongPressGestureRecognizer(gesture =>
{
// Take action based on state
switch (gesture.State)
{
case UIGestureRecognizerState.Began:
var selectedIndexPath = ImageCv.IndexPathForItemAtPoint(gesture.LocationInView(View));
if (selectedIndexPath != null)
ImageCv.BeginInteractiveMovementForItem(selectedIndexPath);
Debug.WriteLine("Gesture Recognition: Activated");
break;
case UIGestureRecognizerState.Changed:
ImageCv.UpdateInteractiveMovement(gesture.LocationInView(View));
Debug.WriteLine("Gesture activated: Item location is changed");
break;
case UIGestureRecognizerState.Ended:
ImageCv.EndInteractiveMovement();
Debug.WriteLine("Gesture activation: complete");
break;
default:
ImageCv.CancelInteractiveMovement();
Debug.WriteLine("Gesture activation: Terminate");
break;
}
});
// Add the custom recognizer to the collection view
ImageCv.AddGestureRecognizer(longPressGesture);
}
UICollectionViewDelegateFlowLayout
using System;
using System.Windows.Input;
using CoreGraphics;
using UIKit;
namespace Sources.CollectionSources
{
public class PostImageFlowLayout : UICollectionViewDelegateFlowLayout
{
private float headerHeight;
private int noOfItems;
private bool isLoading;
public PostImageFlowLayout(int noOfItems, float headerHeight = 0f)
{
this.noOfItems = noOfItems;
this.headerHeight = headerHeight;
}
public override CGSize GetSizeForItem(UICollectionView collectionView, UICollectionViewLayout layout, Foundation.NSIndexPath indexPath)
{
return GetPostCellSize();
}
public override CGSize GetReferenceSizeForHeader(UICollectionView collectionView, UICollectionViewLayout layout, nint section)
{
return new CGSize(collectionView.Frame.Width, headerHeight);
}
public override UIEdgeInsets GetInsetForSection(UICollectionView collectionView, UICollectionViewLayout layout, nint section)
{
return new UIEdgeInsets(0, 0, 0, 0);
}
private CGSize GetPostCellSize()
{
var relativeWidth = (UIScreen.MainScreen.Bounds.Width - 2) / this.noOfItems;
return new CGSize(relativeWidth, relativeWidth);
//return new CGSize(55, 55);
}
}
}
Source
public class PostImageColectionSource : MvxCollectionViewSource
{
private NewPostDetailViewModel newPostDetailViewModel;
private string type;
static NSString animalCellId = new NSString("PostImageCell");
static NSString headerId = new NSString("Header");
List<IAnimal> animals;
protected override NSString DefaultCellIdentifier
{
get
{
return PostImageCell.Key;
}
}
public override System.Collections.IEnumerable ItemsSource
{
get
{
return base.ItemsSource;
}
set
{
base.ItemsSource = value;
CollectionView.ReloadData();
}
}
public PostImageColectionSource(UICollectionView collectionView, NewPostDetailViewModel newPostDetailViewModel) : base(collectionView)
{
this.newPostDetailViewModel = newPostDetailViewModel;
animals = new List<IAnimal>();
for (int i = 0; i < 20; i++)
{
animals.Add(new Monkey(i));
}
}
public override nint NumberOfSections(UICollectionView collectionView)
{
return 1;
}
public override nint GetItemsCount(UICollectionView collectionView, nint section)
{
return 5;// animals.Count;
}
public override UICollectionViewCell GetCell(UICollectionView collectionView, NSIndexPath indexPath)
{
var cell = (PostImageCell)collectionView.DequeueReusableCell(animalCellId, indexPath);
var animal = animals[indexPath.Row];
cell.Result(indexPath.Row);
return cell;
}
public override bool CanMoveItem(UICollectionView collectionView, NSIndexPath indexPath)
{
Debug.WriteLine("Ready to move images");
//System.Diagnostics.Debug.WriteLine("Checking if it can move the item");
return true;
}
public override void MoveItem(UICollectionView collectionView, NSIndexPath sourceIndexPath, NSIndexPath destinationIndexPath)
{
//base.MoveItem(collectionView, sourceIndexPath, destinationIndexPath);
Debug.WriteLine("Start moving images to reorder");
var item = animals[(int)sourceIndexPath.Item];
animals.RemoveAt((int)sourceIndexPath.Item);
animals.Insert((int)destinationIndexPath.Item, item);
}
}
When the GetPostCellSize in PostImageFlowLayout has width and height of around 100, the CanMove and MoveItem in PostImageColectionSource are being called and items are being reordered. But if the GetPostCellSize has width and height of around 50 or 70, even though the gestures are activated, CanMove and MoveItem in PostImageColectionSource are not being called hence cannot be moved.
Can anyone hope me with reordering the images in UICollectionView when the cell size is small like around width and height of 70.
Thank you.
I am tagging swift and objective-C as this issue is related to IOS in general and not xamarin specific

Answer 1

Main issue here is that you need to pass in the collection view to the gesture.LocationInView(View) call instead of the main View. In ViewDidLoad in the UILongPressGestureRecognizer change:
var selectedIndexPath = ImageCv.IndexPathForItemAtPoint(gesture.LocationInView(View));
and
ImageCv.UpdateInteractiveMovement(gesture.LocationInView(View));
to
var selectedIndexPath = ImageCv.IndexPathForItemAtPoint(gesture.LocationInView(ImageCv)); // <-- pass in ImageCV instead of View. (where ImageCV is the collection view)
and
ImageCv.UpdateInteractiveMovement(gesture.LocationInView(ImageCv)); // <-- pass in ImageCV instead of View.
Another thing to note, but not a huge deal, is that PostImageColectionSource is ultimately derived from UICollectionViewSource, which is a combo of UICollectionViewDelegate and UICollectionViewDataSource in one class, but is being assigned to the DataSource property of the collection view. All this means is that though you can implement methods for UICollectionViewDelegate in PostImageColectionSource the delegate methods will not be called on that class since the Delegate property of the collection view is set to the PostImageFlowLayout, which derives ultimately from UICollectionViewDelegate via UICollectionViewDelegateFlowLayout.