我为RecycleViews构建了一个自定义渲染器。
我遇到过一个问题而且我已经没有可能修复的想法，就在这里。
每当用户滚动RecycleView时，屏幕上显示的下一个项目都会按顺序显示，就好像回收不起作用。
您可以在GitHub中找到我的代码： https://github.com/DanielCauser/XamarinHorizontalList
这是一个视频链接，您可以在底部列表中查看我的问题： https://drive.google.com/open?id=1xuuW4479LNiwene0UTMYWl5BPLfT6CJa
这是我在Xamarin.Forms中的视图：
<local:HorizontalViewNative ItemsSource="{Binding Monkeys}"
Grid.Row="5"
VerticalOptions="Start"
ItemHeight="100"
ItemWidth="100">
<local:HorizontalViewNative.ItemTemplate>
<DataTemplate>
<ViewCell>
<ContentView>
<StackLayout WidthRequest="100"
HeightRequest="100">
<Image Source="{Binding Image}" />
<Label Text="{Binding Name}"
LineBreakMode="MiddleTruncation"
HorizontalTextAlignment="Center"
VerticalTextAlignment="Center"/>
</StackLayout>
</ContentView>
</ViewCell>
</DataTemplate>
</local:HorizontalViewNative.ItemTemplate>
</local:HorizontalViewNative>
这是我在Xamarin.Forms项目中的自定义控件：
public class HorizontalViewNative : View
{
public static readonly BindableProperty ItemsSourceProperty =
BindableProperty.Create("ItemsSource", typeof(IEnumerable), typeof(HorizontalViewNative), default(IEnumerable<object>), BindingMode.TwoWay, propertyChanged: ItemsSourceChanged);
public static readonly BindableProperty ItemTemplateProperty =
BindableProperty.Create("ItemTemplate", typeof(DataTemplate), typeof(HVScrollGridView), default(DataTemplate));
public static readonly BindableProperty ItemHeightProperty =
BindableProperty.Create("ItemHeight", typeof(int), typeof(HVScrollGridView), default(int));
public static readonly BindableProperty ItemWidthProperty =
BindableProperty.Create("ItemWidth", typeof(int), typeof(HVScrollGridView), default(int));
public IEnumerable ItemsSource
{
get { return (IEnumerable)GetValue(ItemsSourceProperty); }
set { SetValue(ItemsSourceProperty, value); }
}
public DataTemplate ItemTemplate
{
get { return (DataTemplate)GetValue(ItemTemplateProperty); }
set { SetValue(ItemTemplateProperty, value); }
}
public int ItemHeight
{
get { return (int)GetValue(ItemHeightProperty); }
set { SetValue(ItemHeightProperty, value); }
}
public int ItemWidth
{
get { return (int)GetValue(ItemWidthProperty); }
set { SetValue(ItemWidthProperty, value); }
}
private static void ItemsSourceChanged(BindableObject bindable, object oldValue, object newValue)
{
var itemsLayout = (HorizontalViewNative)bindable;
}
}
这是Android项目中的自定义渲染（使用ViewHolder，View Adapter和View Renderer）。
[assembly: ExportRenderer(typeof(HorizontalViewNative), typeof(AndroidHorizontalViewRenderer))]
namespace XamarinHorizontalList.Droid
{
public class AndroidHorizontalViewRenderer : ViewRenderer<HorizontalViewNative, RecyclerView>
{
private LinearLayoutManager _horizontalLayoutManager;
protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == nameof(Element.ItemsSource))
{
var dataSource = Element.ItemsSource.Cast<object>().ToList();
var adapter = new RecycleViewAdapter(Forms.Context as Android.App.Activity, Element);
adapter.NotifyDataSetChanged();
Control.SetAdapter(adapter);
}
}
protected override void OnElementChanged(ElementChangedEventArgs<HorizontalViewNative> e)
{
base.OnElementChanged(e);
if (e.NewElement != null)
{
var recyclerView = new RecyclerView(Context);
SetNativeControl(recyclerView);
_horizontalLayoutManager = new LinearLayoutManager(Context, OrientationHelper.Horizontal, false);
recyclerView.SetLayoutManager(_horizontalLayoutManager);
Control.SetAdapter(new RecycleViewAdapter(Forms.Context as Android.App.Activity, e.NewElement));
}
}
}
public class RecycleViewAdapter : RecyclerView.Adapter
{
private readonly Activity Context;
private readonly HorizontalViewNative _view;
private readonly IList _dataSource;
public override long GetItemId(int position)
{
return base.GetItemId(position);
}
public override int ItemCount => (_dataSource != null ? _dataSource.Count : 0);
public RecycleViewAdapter(Activity context, HorizontalViewNative view)
{
Context = context;
_view = view;
_dataSource = view.ItemsSource?.Cast<object>()?.ToList();
HasStableIds = true;
}
public override void OnBindViewHolder(RecyclerView.ViewHolder holder, int position)
{
var item = (RecycleViewHolder)holder;
var dataContext = _dataSource[position];
if (dataContext != null)
{
var dataTemplate = _view.ItemTemplate;
ViewCell viewCell;
var selector = dataTemplate as DataTemplateSelector;
if (selector != null)
{
var template = selector.SelectTemplate(_dataSource[position], _view.Parent);
viewCell = template.CreateContent() as ViewCell;
}
else
{
viewCell = dataTemplate?.CreateContent() as ViewCell;
}
item.UpdateUi(viewCell, dataContext, _view);
}
}
public override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)
{
var contentFrame = new FrameLayout(parent.Context)
{
LayoutParameters = new FrameLayout.LayoutParams(ViewGroup.LayoutParams.MatchParent,
ViewGroup.LayoutParams.MatchParent)
{
Height = (int)(_view.ItemHeight * Resources.System.DisplayMetrics.Density),
Width = (int)(_view.ItemWidth * Resources.System.DisplayMetrics.Density)
}
};
contentFrame.DescendantFocusability = DescendantFocusability.AfterDescendants;
var viewHolder = new RecycleViewHolder(contentFrame);
return viewHolder;
}
}
public class RecycleViewHolder : RecyclerView.ViewHolder
{
public RecycleViewHolder(Android.Views.View itemView) : base(itemView)
{
ItemView = itemView;
}
public void UpdateUi(ViewCell viewCell, object dataContext, HorizontalViewNative view)
{
var contentLayout = (FrameLayout)ItemView;
viewCell.BindingContext = dataContext;
viewCell.Parent = view;
var metrics = Resources.System.DisplayMetrics;
// Layout and Measure Xamarin Forms View
var elementSizeRequest = viewCell.View.Measure(double.PositiveInfinity, double.PositiveInfinity, MeasureFlags.IncludeMargins);
var height = (int)((view.ItemHeight + viewCell.View.Margin.Top + viewCell.View.Margin.Bottom) * metrics.Density);
var width = (int)((view.ItemWidth + viewCell.View.Margin.Left + viewCell.View.Margin.Right) * metrics.Density);
viewCell.View.Layout(new Rectangle(0, 0, view.ItemWidth, view.ItemHeight));
// Layout Android View
var layoutParams = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MatchParent, ViewGroup.LayoutParams.MatchParent)
{
Height = height,
Width = width
};
if (Platform.GetRenderer(viewCell.View) == null)
{
Platform.SetRenderer(viewCell.View, Platform.CreateRenderer(viewCell.View));
}
var renderer = Platform.GetRenderer(viewCell.View);
var viewGroup = renderer.View;
viewGroup.LayoutParameters = layoutParams;
viewGroup.Layout(0, 0, width, height);
contentLayout.RemoveAllViews();
contentLayout.AddView(viewGroup);
}
}
}
答案 0 :(得分：0)
是的，所以我能够解决渲染器的问题。
1 - 我搞乱了适配器调用，我调用了两次，一次在OnElementChanged中，一次在OnElementOnProperty中更改。
2 - 我覆盖了适配器的get item id，使视图正确排序！
3 - 我调整了所有图片的大小，我得到了一个奇怪的内存不足异常，通过缩小所有图片决定显示它们。