I'm writing a custom render for Xamarins UITableView that allows drag and drop.
I implemented the UITableViewDragDelegate and DropDelegate.
When I use UIDropOperation.Copy in the DropSessionDidUpdate function all is working fine as PerformDrop is called afterwards. The problem is Copy adds this nasty + icon to the cell while dragging which I don't want to have.
If I return UIDropOperation.Move then the + icon is gone. However PerformDrop is not called then anymore.
I found several hints to what could be wrong, for example do a clean:
UIDropInteractionDelegate performDrop not called?
In the same post one answer explains that Move can only be used if session.allowsMove is true.
So I implemented the CanMoveRow in my DataSource:
public override bool CanMoveRow(UITableView tableView, NSIndexPath indexPath)
{
return true;
}
but that didn't fix the issue. At least I can confirm that session.allowsMove is always true now.
In another thread (where I lost the link) for MacOS it was said that perform drop doesn't work if NSItemProvider of the UIDragItem doesn't have an object associated to. So I Implemented a wrapper for my Forms object and assigned it to the NSItemProvider:
public override UIDragItem[] GetItemsForBeginningDragSession(UITableView tableView, IUIDragSession session, NSIndexPath indexPath)
{
if (list.ItemsSource is IList source) //List is the instance of the Xamarin Forms ListView
{ //Check is always fulfilled
var item = NSObjectWrapper.Wrap(source[indexPath.Row]);
var itemProvider = new NSItemProvider(item, item.GetType().ToString());
var dragItem = new UIDragItem(itemProvider);
dragItem.LocalObject = item;
return new UIDragItem[] { dragItem };
}
return null;
}
but, still no change.
What am I doing wrong, how can I get move to perform a drop or how can I get rid of the + icon in the copy view?
Thank you!
Related
How can I stop a diffable data source scrolling the view to the top after applying the snapshot. I currently have this...
fileprivate func configureDataSource() {
self.datasource = UICollectionViewDiffableDataSource<Section, PostDetail>(collectionView: self.collectionView) {
(collectionView: UICollectionView, indexPath: IndexPath, userComment: PostDetail) -> UICollectionViewCell? in
guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: PostDetailCell.reuseIdentifier, for: indexPath) as? PostDetailCell else { fatalError("Cannot create cell")}
cell.user = self.user
cell.postDetail = userComment
cell.likeCommentDelegate = self
return cell
}
var snapshot = NSDiffableDataSourceSnapshot<Section, PostDetail>()
snapshot.appendSections([.main])
snapshot.appendItems(self.userComments)
self.datasource.apply(snapshot, animatingDifferences: true)
}
fileprivate func applySnapshot() {
//let contentOffset = self.collectionView.contentOffset
var snapshot = NSDiffableDataSourceSnapshot<Section, PostDetail>()
snapshot.appendSections([.main])
snapshot.appendItems(self.userComments)
self.datasource.apply(snapshot, animatingDifferences: false)
//self.collectionView.contentOffset = contentOffset
}
store the offset, then reapply it. Sometimes it works perfectly and sometimes the view jumps. Is there a better way of doing this?
The source of this problem is probably your Item identifier type - the UserComment.
Diffable data source uses the hash of your item identifier type to detect if it is a new instance or an old one which is represented currently.
If you implement Hashable protocol manually, and you use a UUID which is generated whenever a new instance of the type is initialized, this misguides the Diffable data source and tells it this is a new instance of item identifier. So the previous ones must be deleted and the new ones should be represented. This causes the table or collection view to scroll after applying snapshot.
To solve that replace the uuid with one of the properties of the type that you know is unique or more generally use a technique to generate the same hash value for identical instances.
So to summarize, the general idea is to pass instances of the item identifiers with the same hash values to the snapshot to tell the Diffable data source that these items are not new and there is no need to delete previous ones and insert these ones. In this case you will not encounter unnecessary scrolls.
Starting from iOS 15
dataSource.applySnapshotUsingReloadData(snapshot, completion: nil)
Resets the UI to reflect the state of the data in the snapshot without computing a diff or animating the changes
First up: in most cases #Amirrezas answer will be the correct reason for the problem. In my case it was not the item, but the section identifier that caused the problem. That was Hashable and Identifiable with correct values, but it was a class, and therefore the hash functions were never called. Took me a while to spot that problem. Changing to a struct (and therefore adopting some things ;) ) helped in my case.
For reference here's a link to the topic on the Apple-Dev forums: https://developer.apple.com/forums/thread/657499
Hope my answer helps somebody :)
You'd think that any of these methods would work:
https://developer.apple.com/documentation/uikit/uicollectionviewdelegate/1618007-collectionview
https://developer.apple.com/documentation/uikit/uicollectionviewlayout/1617724-targetcontentoffset
But (in my case) they did not. You might get more mileage out of them, I am doing some crazy stuff with a custom UICollectionViewCompositionalLayout
What I did get to work is manually setting the offset in my custom layout class:
override func finalizeCollectionViewUpdates() {
if let offset = collectionView?.contentOffset {
collectionView?.contentOffset = targetContentOffset(forProposedContentOffset: offset)
}
super.finalizeCollectionViewUpdates()
}
where I have targetContentOffset also overridden and defined (I tried that first, didn't work, figured it was cleanest to just use that here. I suspect if you define targetContentOffset on the delegate without overriding it in the layout the above will also work, but you already need a custom layout to get this far so it's all the same.)
As I said in other questions I am very newbie in .Net technologies. Now I am starting with an exercise using the Xamarin Crossplatform (Xamarin.IOS for the moment). But I have a problem with this code, it's working, but the method ForceUpdateSize() crashes the application if I have more than 6 elements in the table?. When I remove the method the app works fine, but then the text is overlapped.
This is the method that is filling my table:
public sealed class AutoViewCellRenderer : ViewCellRenderer
{
public override UITableViewCell GetCell(Cell item, UITableViewCell reusableCell, UITableView tv)
{
ViewCell vc = item as ViewCell;
if (vc != null)
{
var sr = vc.View.Measure(tv.Frame.Width, double.PositiveInfinity, MeasureFlags.IncludeMargins);
if (vc.Height != sr.Request.Height)
{
sr = vc.View.Measure(tv.Frame.Width, double.PositiveInfinity, MeasureFlags.IncludeMargins);
vc.Height = sr.Request.Height;
//vc.ForceUpdateSize(); --> Text ovelpping effect if I remove this method, but the app doesn't crash
}
}
return GetCell(item, reusableCell, tv);
}
}
Can someone help me to understand what I am doing wrong?
Thanks in advance to everybody!
Try this:
//vc.ForceUpdateSize(); --> Text ovelpping effect if I remove this method, but the app doesn't crash
tv.BeginUpdates();
tv.EndUpdates();
I have found this in an older post, but sadly I can't find it anymore.
Also take a look at this: https://github.com/xamarin/Xamarin.Forms/issues/4012
I think the Xamarin Community knows well about this and is addressing it in this Thread.
I'm looking for any possible way of passing the result of an networking update to a button in a UITableViewCell as a closure.
I have some UITableViewCells that are products. In these cells, I have an 'Add to Cart' button. I set a buttonTap closure in my UITableViewCell cellforRowAtIndexPath method, setup a touch handler within the cell for the button, and when that handler is called, execute the buttonTap closure. I handle my cart updating on a cart object which lives on the main controller.
The result of the cart update action returns true if they can add more items to their cart. Then, I update the button accordingly. I like this approach because I don't have to deal with delegates and I can keep all of the cart logic itself far far away from the cell; the cell just knows how to make a button enabled/disabled/loading/etc.
/// Buttom tap callback callback.
public typealias Selection = () -> Bool
class MealTableViewCell: UITableViewCell {
var buttonTap: Selection?
// Runs when tapping the button
func didTapAdd() {
if let buttonBlock = buttonTap {
self.button.isLoading = true
// Simulate loading
DispatchQueue.main.asyncAfter(deadline: .now() + 0.4) {
self.button.enabled = buttonBlock()
self.button.isLoading = false
}
}
}
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = .... (fetch cell)
cell.buttonTap = {
// returns true if the user can add more items to their cart
return self.cart.update(product: product, quantity: 1)
}
}
My question is that currently, my cart is all local with no API calls. I'm currently switching the cart over to an API driven one, with network calls to add and remove items. That means I can no longer return a BOOL, or return at all, from my cart.update(product:,quantity:) method as it is now an async call.
So, I can do something like rewrite that method signature to be
self.cart.update(product: product, quantity: 1, success: { canAddMore in
// API call succeeded
}, failure: { error in
// fall failed
})
The question is that how can I pass canAddMore to the tableViewCell? If I redefine what Selection means to take in a block that takes a bool as a param, I can't pass that param in from the controller as it would only be passed in when the block is executed on the cell itself.
How can I do something like
cell.buttonTap = {
cell.buttonTap = {
self.cart.update(product: product, quantity: 1), success: { canAddMore in
// !!!! What can I call here to pass canAddMore to the cell.
}, failure: { error in
}
}
}
canAddMore can be any value really, a BOOL is just this example. My big goal is to avoid coupling any knowledge of the cell's loading and buttons to the controller itself. If I use delegates, I would have to have a two way delegate makes the cell a delegate of the controller, and I've always felt that's the sort of wrong direction to approach this. I'm not positive it's really possible to pass the result of a closure back to the cell, but I am hoping there is!
EDIT: The big question I'm really trying to answer is if it is at all possible to pass data back to the cell (or any object) that originally called closure through that closure. There's a million ways to do data modifications in a table view, but that's sort of the main thing I'm trying to address.
I'm also "looking" to avoid storing the canAddMore state (e.g. the quantity remaining for that product) in the main 'products' array that powers the tableview. The initial state is set there, returned from a /products endpoint, but after that, inventory being available or not is returned by the carts API action.
I don't think you want to do what you think you want to do :)
In a nutshell, instead of trying to "talk back" to the cell that called the closure, you probably want to track the "canAddMore" state of each product in your Products data array, and then update the table row(s) when the state changes. So...
User taps "Add to Cart"
Give visual feedback in that row to show that you are processing the tap (gray out the button, or show a spinner, whatever looks good)
Call back to the closure to start the Add-to-cart API call
When the API call returns, update your local Products data to indicate the "canAddMore" state
reload the row(s) in the table to update the Button (make it active, inactive, change the title, whatever)
You almost certainly need to be doing something similar anyway, so the Buttons in each row will be updated when the user scrolls and the cells are reused.
A general approach is to update the cell's content with tableView.reloadRows(at: [indexPath], with: true) in your callback. This will call func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell for the specified cell. Don't forget that this has to be done in the main queue.
I have read many tutorial out there for UICollectionView for both iOS and Xamarin.iOS
Everybody has shown same sample tutorial with one image inside UICollectionViewCell
Desired output
UICollectionViewCell with custom design
What I have done
This is what I have achieved so far.. please ignore the bad design :P
Problem
When I Click on Book button, it triggers the event multiple times. The weird thing is that its not consistent, sometimes it will trigger only once some time twice or some time three times or whatever...
Code Snippet
List<MeetingRoom> data = new List<MeetingRoom>();
async public override void ViewDidLoad()
{
base.ViewDidLoad();
data = await DashboardServices.getMeetingRooms(DateTime.Now);
MeetingRoomCollection.WeakDataSource = this;
}
public nint GetItemsCount(UICollectionView collectionView, nint section)
{
var count = data.Count;
return count;
}
public UICollectionViewCell GetCell(UICollectionView collectionView, NSIndexPath indexPath)
{
var cell = (MeetingRoomCell)collectionView.DequeueReusableCell("cell", indexPath);
cell.RoomName.Text = data[indexPath.Row].Room_Name;
cell.Status.Text = data[indexPath.Row].Availability;
cell.BookButton.Tag = indexPath.Row;
cell.BookButton.TouchUpInside += Cell_BookButton_TouchUpInside;
return cell;
}
void Cell_BookButton_TouchUpInside(object sender, EventArgs e)
{
var x = sender as UIButton;
Debug.WriteLine("index : {0}, status : {1}", (int)x.Tag, data[(int)x.Tag].Availability);
this.PerformSegue("segue_bookRoom", this);
}
Please suggest what needs to be done to fix this issue, any reference to available tutorial would be appreciated. It will be great if Xamarin.iOS hint is there..
One possible way to solve this issue is to unsubscribe from event before subscribing it, this way it will prevent multiple calls especially if this item is recycled in list.
cell.BookButton.TouchUpInside -= Cell_BookButton_TouchUpInside;
cell.BookButton.TouchUpInside += Cell_BookButton_TouchUpInside;
I'm using MvvmCross with UICollectionView.
Bindings work perfectly, I have all my data properly displayed, and even if I select an item in CollectionView it gets properly set in my ViewModel.
For SelectedItem I use the following binding:
set.Bind(_collectionViewSource).For(x => x.SelectedItem).To(vm => vm.SelectedMachine);
The only problem I have is that I want a first CollectionViewItem to be selected initially.
As the sources of MvvmCross say that's not supported currently (in the setter for SelectedItem):
// note that we only expect this to be called from the control/Table
// we don't have any multi-select or any scroll into view functionality here
So, what's the best way to perform initial pre-selection of an item? What's the place I can call _collectionView.SelectItem from?
I tried calling it when collection changes, but that doesn't seem to work.
If you need this functionality, you should be able to inherit from MvxCollectionViewSource and to add a property something like
public event EventHandler SelectedItemExChanged;
public object SelectedItemEx
{
get { return base.SelectedItem; }
set
{
base.SelectedItem = value;
var index = FindIndexPath(value); // find the NSIndexPath of value in the collection
if (index != null)
_collectionView.SelectItem(index, true, UICollectionViewScrollPosition.CenteredHorizontally);
var handler = SelectedItemExChanged;
if (handler != null)
handler(this, EventArgs.Empty);
}
}
That can then be bound instead of SelectedItem
What's the place I can call _collectionView.SelectItem from? I tried calling it when collection changes, but that doesn't seem to work.
If that doesn't work, then I'm not sure - you are probably heading into animation timing problems - see questions like uicollectionview select an item immediately after reloaddata? - maybe try editing your question to post a bit more of your code - something that people can more easily hope with debugging.