android - RecycleView 回收无法正常工作

Question

我已经为 RecycleViews 构建了一个自定义渲染器。

我一直遇到一个问题，我想不出可能的解决办法，就在这里。

每当用户滚动 RecycleView 时，屏幕上显示的下一个项目就会乱序显示，就好像 Recycle 不工作一样。

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，您可以在其中确切地看到底部列表中我的问题是什么: https://drive.google.com/open?id=1xuuW4479LNiwene0UTMYWl5BPLfT6CJa

这是我在 Xamarin.Forms 中的 View :

<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;
        }
    }

这是我在 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);
            }
        }
    }

Answer 1

是的，所以我能够解决渲染器的问题。

1 - 我弄乱了适配器调用，我调用了两次，一次是在 OnElementChanged 中，一次是在 OnElementOnProperty changed 中。

2 - 我重写了适配器的获取项目 ID，使 View 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，通过缩小它们决定显示所有图片。