UWP VirtualizedVariableSizedGridView 支持可虚拟化可变大小Item的View

Posted 2020-07-24 法的空间

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上篇UWP VirtualizedVariableSizedGridView 支持可虚拟化可变大小Item的View（一）讲到该控件的需要和设计过程。

这篇讲讲开发过程中一些重要问题解决。

1.支持ISupportIncrementalLoading，实现HasMoreItems属性和LoadMoreItemsAsync方法

因为我们上篇里面讲过，需要把源数据分成一个一个的Group作为GirdView的源，

所以LoadMoreItemsAsync方法里面我做了以下的实现：

        public IAsyncOperation<LoadMoreItemsResult> LoadMoreItemsAsync(uint count)
        {
            IAsyncOperation<LoadMoreItemsResult> result = rowAdapter.LoadMoreItemsAsync(count);
            if (rowAdapter.Count > 0)
            {
                for (int i = this.Count; i < rowAdapter.Count; i++)
                {
                    if (rowAdapter.SourceList.Count / rowAdapter.rowItemsCount > i)
                    {
                        var item = this.ElementAtOrDefault(i);
                        if (item == null)
                        {
                            this.Insert(i, rowAdapter[i]);
                        }
                    }
                }
            }

            return result;
        }

应该还是比较清楚的，当源数据里面的个数超过了RowItemsCount的时候，我们才插入Item。

也就是说。当满15个Item的时候我们才插入第1个Row Item，当满30个Item的时候我们插入第2个Row Item......

可能有人会说，如果源数据不是15个整数，那怎么办呢？？嗯，我也遇到了这个问题，当然，HasMoreItems属性也需要作相应的实现

        public bool HasMoreItems
        {
            get
            {
                var hasMoreItems = rowAdapter.HasMoreItems;
   
                if (!hasMoreItems)
                {
                    if (rowAdapter.Count > 0 && this.Count < rowAdapter.Count)
                    {
                        for (int i = this.Count; i < rowAdapter.Count; i++)
                        {
                            //sometime it will miss some indexs in LoadMoreItemsAsync method,
                            //if hasMoreItems is false, that means not more items,
                            //so at that monment we should add the missed items.
                            //if (rowAdapter.SourceList.Count / rowAdapter.rowItemsCount <= i)
                            {
                                var item = this.ElementAtOrDefault(i);
                                if (item == null)
                                {
                                    this.Insert(i, rowAdapter[i]);
                                }
                            }
                        }
                    }
                }
                return hasMoreItems;
            }
        }

当HasMoreItems为false的时候，就是说这个源不会有更多的数据了，所以这时候我们应该把剩余的Item都加入到下一个Row Item里面去。

2.当Window size 改变的时候，实现不同的可变大小结构。

public class ResizeableItems : List<ResizeableItem>

每一种结构，我用一个ResizeableItem来表示。

比如window 最小的时候这种结构。

                list = new List<Resizable>();
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });

                var c1 = new ResizeableItem() { Columns = 2, Items = list,               Min = windowMinwidth + +1, Max = windowMinwidth + rangwidth * 1 };
                _resizeableItems.Add(c1);

设置GirdView里面的每个Item的宽高比2：1，设置ResizeableItem的最小和最大值，这个意思就是当window 到达MIn和Max的这个区间的时候就使用这个结构。

然后也设置出其它的结构样式。（PS:我这里还没找到Get 最小window 宽度的办法，好像只能设置，如果有办法的朋友请留言一下）

                 _resizeableItems = new ResizeableItems();

                //ApplicationView.GetForCurrentView().SetPreferredMinSize(new Windows.Foundation.Size(200, 200));

                double windowMinwidth = 500;
                double windowMaxwidth = DeviceInfo.DeviceScreenSize.Width;
                double rangwidth = (windowMaxwidth - windowMinwidth) / 4.0;

                #region 4
                var list = new List<Resizable>();
                list.Add(new Resizable() { Width = 2, Height = 2 });
                list.Add(new Resizable() { Width = 1, Height = 2 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 2 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });

                var c4 = new ResizeableItem() { Columns = 4, Items = list, Min = windowMinwidth + rangwidth * 3 + 1, Max = double.PositiveInfinity };
                _resizeableItems.Add(c4);
                #endregion

                #region 3
                list = new List<Resizable>();
                list.Add(new Resizable() { Width = 2, Height = 2 });
                list.Add(new Resizable() { Width = 1, Height = 2 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 2 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });

                var c3 = new ResizeableItem() { Columns = 3, Items = list, Min = windowMinwidth + rangwidth * 2 + 1, Max = windowMinwidth + rangwidth * 3 };
                _resizeableItems.Add(c3);
                #endregion

                #region 2
                list = new List<Resizable>();
                list.Add(new Resizable() { Width = 2, Height = 2 });
                list.Add(new Resizable() { Width = 1, Height = 2 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 2 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });
                list.Add(new Resizable() { Width = 1, Height = 1 });

                var c2 = new ResizeableItem() { Columns = 2, Items = list, Min = windowMinwidth + rangwidth * 1 + 1, Max = windowMinwidth + rangwidth * 2 };
                _resizeableItems.Add(c2);
                #endregion

                #region 1
                list = new List<Resizable>();
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });
                list.Add(new Resizable() { Width = 2, Height = 1 });

                var c1 = new ResizeableItem() { Columns = 2, Items = list, Min = windowMinwidth + +1, Max = windowMinwidth + rangwidth * 1 };
                _resizeableItems.Add(c1);
                #endregion

View Code

这样我们就设置好了，到达多少size的时候使用什么结构模板了。。

最后我们只需要在控件的MeasureOverrid中去设置，GridView的Item的样式就好了.

        protected override Size MeasureOverride(Size availableSize)
        {
            if (!PlatformIndependent.IsWindowsPhoneDevice)
            {
                OnMeasureOverride(availableSize);
            }
            return base.MeasureOverride(availableSize);
        }
        
         private void OnMeasureOverride(Size availableSize)
        {
            if (ItemsSource != null && ItemsSource is IResizeableItems && availableSize != Size.Empty)
            {
                var resizeableItem = ResizeableItems.GetItem(availableSize.Width);

                if (resizeableItem != null)
                {
                    resizeableItem.ItemWidth = (int)(availableSize.Width / resizeableItem.Columns - 7);

                    foreach (var item in this.Items)
                    {
                        var gridviewItem = this.ContainerFromItem(item) as ListViewItem;
                        //not null, it\'s in viewport, so it need to update.
                        if (gridviewItem != null && gridviewItem.ContentTemplateRoot != null)
                        {
                            var gridview = gridviewItem.ContentTemplateRoot as VariableSizedGridView;
                            gridview.ResizeableItem = null;
                            gridview.ResizeableItem = resizeableItem;

                        }
                    }
                }

            }
        }

3.ListViewItem默认模板的修改
在使用这个的时候因为其实是个ListView,所以当你点击到GridView外面的时候就点击到了ListLViewItem上面，会有些你不想要的效果，比如PointerDown。

第一次用VS拿到ListViewItem的模板的时候发现没地方可能修改这个动画呢？？？

再查了下MSDN,发现原来，ListViewItem是有2套模板的，

Default style

When the ListView\'s ItemsPanel is an ItemsStackPanel (the default) or ItemsWrapGrid, this template is used to show the data items. This template uses aListViewItemPresenter instead of a UIElement tree to improve grid performance.

这个模板跟我从VS里面拿到的是一样的。

<!-- Default style for Windows.UI.Xaml.Controls.ListViewItem -->
<Style TargetType="ListViewItem">
    <Setter Property="FontFamily" Value="{ThemeResource ContentControlThemeFontFamily}" />
    <Setter Property="FontSize" Value="{ThemeResource ControlContentThemeFontSize}" />
    <Setter Property="Background" Value="Transparent"/>
    <Setter Property="TabNavigation" Value="Local"/>
    <Setter Property="IsHoldingEnabled" Value="True"/>
    <Setter Property="Margin" Value="0,0,18,2"/>
    <Setter Property="HorizontalContentAlignment" Value="Left"/>
    <Setter Property="VerticalContentAlignment" Value="Top"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="ListViewItem">
                <ListViewItemPresenter
                    ContentTransitions="{TemplateBinding ContentTransitions}"
                    Padding="{TemplateBinding Padding}"
                    SelectionCheckMarkVisualEnabled="True"
                    CheckHintBrush="{ThemeResource ListViewItemCheckHintThemeBrush}"
                    CheckSelectingBrush="{ThemeResource ListViewItemCheckSelectingThemeBrush}"
                    CheckBrush="{ThemeResource ListViewItemCheckThemeBrush}"
                    DragBackground="{ThemeResource ListViewItemDragBackgroundThemeBrush}"
                    DragForeground="{ThemeResource ListViewItemDragForegroundThemeBrush}"
                    FocusBorderBrush="{ThemeResource ListViewItemFocusBorderThemeBrush}"
                    PlaceholderBackground="{ThemeResource ListViewItemPlaceholderBackgroundThemeBrush}"
                    PointerOverBackground="{ThemeResource ListViewItemPointerOverBackgroundThemeBrush}"
                    SelectedBorderThickness="{ThemeResource ListViewItemCompactSelectedBorderThemeThickness}"
                    SelectedBackground="{ThemeResource ListViewItemSelectedBackgroundThemeBrush}"
                    SelectedForeground="{ThemeResource ListViewItemSelectedForegroundThemeBrush}"
                    SelectedPointerOverBackground="{ThemeResource ListViewItemSelectedPointerOverBackgroundThemeBrush}"
                    SelectedPointerOverBorderBrush="{ThemeResource ListViewItemSelectedPointerOverBorderThemeBrush}"
                    DisabledOpacity="{ThemeResource ListViewItemDisabledThemeOpacity}"
                    DragOpacity="{ThemeResource ListViewItemDragThemeOpacity}"
                    ReorderHintOffset="{ThemeResource ListViewItemReorderHintThemeOffset}"
                    HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                    VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
                    PointerOverBackgroundMargin="1"
                    ContentMargin="4" />
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

When the ListView\'s ItemsPanel is not an ItemsStackPanel (the default) or ItemsWrapGrid, this template is used to show the data items. This template uses aUIElement tree and visual states instead of a ListViewItemPresenter.

这个模板我就不贴了，比较多，MSDN地址

总结：

虽然说这个控件已经满足了Boss的需求，但是我还是觉得有一些需要改进的。

1.UI Virtualized

如果说GridView里面的Item个数被用户设置的很多，这个必定是很占用内存的。

实际Debug，也发现，Live Visual Tree里面有3个ListViewItem.

感觉内存中不需要这么多个ListViewItem 来循环回收利用，我的猜想是微软做了上下各一个Item的缓存来提高Scrolling的流畅。

但对于这个控件来说，内存里面的UI Item 会有3*15个，因为我们知道VariableSizedWrapGrid是不支持UI虚拟化的。

2.没有对Insert，Delete进行处理。

这个控件还有一个限制，就是源是一个固定个数或者是ISupportIncrementalLoading，如果在过程中add，insert，delete的话，暂时没有进行处理。

只对Reset这种情况进行了处理。

        private void ObservableRowAapter_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            switch (e.Action)
            {
                case NotifyCollectionChangedAction.Add:
                    break;
                case NotifyCollectionChangedAction.Move:
                    break;
                case NotifyCollectionChangedAction.Remove:
                    break;
                case NotifyCollectionChangedAction.Replace:
                    break;
                case NotifyCollectionChangedAction.Reset:
                    if (this.Count>0)
                    {
                        this.Clear();
                    }
                    break;
                default:
                    break;
            }
        }

希望有好想法的童鞋能留言，大家讨论共同进步。。

为了部落！

开源有益，GitHub源代码地址

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