我正在尝试在Xamarin Forms中创建一个自定义视图，以将其转换为IOS中的UICollectionView。
这第一件事很容易做到：
视图：
public class CollectionView : View
{
}
渲染器：
public class CollectionViewRenderer : ViewRenderer<CollectionView, UICollectionView>
{
protected override void OnElementChanged(ElementChangedEventArgs<CollectionView> e)
{
base.OnElementChanged(e);
if (Control == null)
{
SetNativeControl(new UICollectionView(new CGRect(0, 0, 200, 200), new UICollectionViewFlowLayout()));
}
if (e.NewElement != null)
{
...
Control.Source = new CollectionViewSource(a, this);
Control.ReloadData();
}
}
}
现在，我想用DataTemplates（从DataTemplateSelector）提供此CollectionView。但是我找不到注册类的方法：
在模板中，您可以执行以下操作：
Template.CreateContent();
获取UI元素。
但是我如何在collectionView中注册它以便在CollectionSource中出队
例如：
CollectionView.RegisterClassForCell(typeof(????), "CellId");
希望对您有帮助！！！
using System;
using CoreGraphics;
using Foundation;
using UIKit;
namespace MyApp.Forms.Controls
{
public class GridCollectionView : UICollectionView
{
public GridCollectionView () : this (default(CGRect))
{
}
public GridCollectionView(CGRect frm)
: base(frm, new UICollectionViewFlowLayout())
{
AutoresizingMask = UIViewAutoresizing.All;
ContentMode = UIViewContentMode.ScaleToFill;
RegisterClassForCell(typeof(GridViewCell), new NSString (GridViewCell.Key));
}
public bool SelectionEnable
{
get;
set;
}
public double RowSpacing
{
get
{
return ((UICollectionViewFlowLayout)this.CollectionViewLayout).MinimumLineSpacing;
}
set
{
((UICollectionViewFlowLayout)this.CollectionViewLayout).MinimumLineSpacing = (nfloat)value;
}
}
public double ColumnSpacing
{
get
{
return ((UICollectionViewFlowLayout)this.CollectionViewLayout).MinimumInteritemSpacing;
}
set
{
((UICollectionViewFlowLayout)this.CollectionViewLayout).MinimumInteritemSpacing = (nfloat)value;
}
}
public CGSize ItemSize
{
get
{
return ((UICollectionViewFlowLayout)this.CollectionViewLayout).ItemSize;
}
set
{
((UICollectionViewFlowLayout)this.CollectionViewLayout).ItemSize = value;
}
}
public override UICollectionViewCell CellForItem(NSIndexPath indexPath)
{
if (indexPath == null)
{
//calling base.CellForItem(indexPath) when indexPath is null causes an exception.
//indexPath could be null in the following scenario:
// - GridView is configured to show 2 cells per row and there are 3 items in ItemsSource collection
// - you're trying to drag 4th cell (empty) like you're trying to scroll
return null;
}
return base.CellForItem(indexPath);
}
public override void Draw (CGRect rect)
{
this.CollectionViewLayout.InvalidateLayout ();
base.Draw (rect);
}
public override CGSize SizeThatFits(CGSize size)
{
return ItemSize;
}
}
}
using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Linq;
using Foundation;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
using MyApp.Controls;
using System.Collections.Generic;
[assembly: ExportRenderer (typeof(GridView), typeof(GridViewRenderer))]
namespace MyApp.Controls
{
public class GridViewRenderer: ViewRenderer<GridView,GridCollectionView>
{
private GridDataSource _dataSource;
public GridViewRenderer ()
{
}
public int RowsInSection(UICollectionView collectionView, nint section)
{
return ((ICollection) this.Element.ItemsSource).Count;
}
public void ItemSelected(UICollectionView tableView, NSIndexPath indexPath)
{
var item = this.Element.ItemsSource.Cast<object>().ElementAt(indexPath.Row);
this.Element.InvokeItemSelectedEvent(this, item);
}
public UICollectionViewCell GetCell(UICollectionView collectionView, NSIndexPath indexPath)
{
var item = this.Element.ItemsSource.Cast<object>().ElementAt(indexPath.Row);
var viewCellBinded = (this.Element.ItemTemplate.CreateContent() as ViewCell);
if (viewCellBinded == null) return null;
viewCellBinded.BindingContext = item;
return this.GetCell(collectionView, viewCellBinded, indexPath);
}
protected virtual UICollectionViewCell GetCell(UICollectionView collectionView, ViewCell item, NSIndexPath indexPath)
{
var collectionCell = collectionView.DequeueReusableCell(new NSString(GridViewCell.Key), indexPath) as GridViewCell;
if (collectionCell == null) return null;
collectionCell.ViewCell = item;
return collectionCell;
}
protected override void OnElementChanged (ElementChangedEventArgs<GridView> e)
{
base.OnElementChanged (e);
if (e.OldElement != null)
{
Unbind (e.OldElement);
}
if (e.NewElement != null)
{
if (Control == null)
{
var collectionView = new GridCollectionView() {
AllowsMultipleSelection = false,
SelectionEnable = e.NewElement.SelectionEnabled,
ContentInset = new UIEdgeInsets ((float)this.Element.Padding.Top, (float)this.Element.Padding.Left, (float)this.Element.Padding.Bottom, (float)this.Element.Padding.Right),
BackgroundColor = this.Element.BackgroundColor.ToUIColor (),
ItemSize = new CoreGraphics.CGSize ((float)this.Element.ItemWidth, (float)this.Element.ItemHeight),
RowSpacing = this.Element.RowSpacing,
ColumnSpacing = this.Element.ColumnSpacing
};
Bind (e.NewElement);
collectionView.Source = this.DataSource;
//collectionView.Delegate = this.GridViewDelegate;
SetNativeControl (collectionView);
}
}
}
private void Unbind (GridView oldElement)
{
if (oldElement == null) return;
oldElement.PropertyChanging -= this.ElementPropertyChanging;
oldElement.PropertyChanged -= this.ElementPropertyChanged;
var itemsSource = oldElement.ItemsSource as INotifyCollectionChanged;
if (itemsSource != null)
{
itemsSource.CollectionChanged -= this.DataCollectionChanged;
}
}
private void Bind (GridView newElement)
{
if (newElement == null) return;
newElement.PropertyChanging += this.ElementPropertyChanging;
newElement.PropertyChanged += this.ElementPropertyChanged;
var source = newElement.ItemsSource as INotifyCollectionChanged;
if (source != null)
{
source.CollectionChanged += this.DataCollectionChanged;
}
}
private void ElementPropertyChanged (object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
if (e.PropertyName == GridView.ItemsSourceProperty.PropertyName)
{
var newItemsSource = this.Element.ItemsSource as INotifyCollectionChanged;
if (newItemsSource != null)
{
newItemsSource.CollectionChanged += DataCollectionChanged;
this.Control.ReloadData();
}
}
else if(e.PropertyName == "ItemWidth" || e.PropertyName == "ItemHeight")
{
this.Control.ItemSize = new CoreGraphics.CGSize ((float)this.Element.ItemWidth, (float)this.Element.ItemHeight);
}
}
private void ElementPropertyChanging (object sender, PropertyChangingEventArgs e)
{
if (e.PropertyName == "ItemsSource")
{
var oldItemsSource = this.Element.ItemsSource as INotifyCollectionChanged;
if (oldItemsSource != null)
{
oldItemsSource.CollectionChanged -= DataCollectionChanged;
}
}
}
private void DataCollectionChanged (object sender, NotifyCollectionChangedEventArgs e)
{
InvokeOnMainThread (()=> {
try
{
if(this.Control == null)
return;
this.Control.ReloadData();
// TODO: try to handle add or remove operations gracefully, just reload the whole collection for other changes
// InsertItems, DeleteItems or ReloadItems can cause
// *** Assertion failure in -[XLabs_Forms_Controls_GridCollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:],
// BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit_Sim/UIKit-3512.30.14/UICollectionView.m:4324
// var indexes = new List<NSIndexPath>();
// switch (e.Action) {
// case NotifyCollectionChangedAction.Add:
// for (int i = 0; i < e.NewItems.Count; i++) {
// indexes.Add(NSIndexPath.FromRowSection((nint)(e.NewStartingIndex + i),0));
// }
// this.Control.InsertItems(indexes.ToArray());
// break;
// case NotifyCollectionChangedAction.Remove:
// for (int i = 0; i< e.OldItems.Count; i++) {
// indexes.Add(NSIndexPath.FromRowSection((nint)(e.OldStartingIndex + i),0));
// }
// this.Control.DeleteItems(indexes.ToArray());
// break;
// default:
// this.Control.ReloadData();
// break;
// }
}
catch { } // todo: determine why we are hiding a possible exception here
});
}
private GridDataSource DataSource
{
get
{
return _dataSource ?? (_dataSource = new GridDataSource (GetCell, RowsInSection,ItemSelected));
}
}
protected override void Dispose (bool disposing)
{
base.Dispose (disposing);
if (disposing && _dataSource != null)
{
Unbind (Element);
_dataSource.Dispose ();
_dataSource = null;
}
}
}
}
有关更多信息，请单击此处获取自定义类，并单击此处获取渲染器类
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