UWP中实现大爆炸效果（二）

public sealed class BigbangView : ListView
{
    public BigbangView()
    {
        this.DefaultStyleKey = typeof(BigbangView);
    }
}

public BigbangView()
{
    this.DefaultStyleKey = typeof(BigbangView);
    this.Loaded += BigbangView_Loaded;
    this.Unloaded += BigbangView_Unloaded;
    this.SelectionChanged += BigbangView_SelectionChanged;

    PointerPressedHandler = new PointerEventHandler(_PointerPressed);
    PointerReleasedHandler = new PointerEventHandler(_PointerReleased);
    PointerMovedHandler = new PointerEventHandler(_PointerMoved);
}

protected override void OnApplyTemplate()
{
    base.OnApplyTemplate();
    RootBorder = GetTemplateChild("RootBorder") as Border;
    ItemsGrid = GetTemplateChild("ItemsGrid") as Grid;
    ScrollViewer = GetTemplateChild("ScrollViewer") as ScrollViewer;

    ScrollViewer.AddHandler(UIElement.PointerPressedEvent, PointerPressedHandler, true);
    ScrollViewer.AddHandler(UIElement.PointerReleasedEvent, PointerReleasedHandler, true);
    ScrollViewer.AddHandler(UIElement.PointerCanceledEvent, PointerReleasedHandler, true);
    ScrollViewer.AddHandler(UIElement.PointerExitedEvent, PointerReleasedHandler, true);
    ScrollViewer.ViewChanging += _ScrollViewer_ViewChanging;
}

private Dictionary<UIElement, Rect> _ChildrenRects;

public Dictionary<UIElement, Rect> ChildrenRects
{
    get
    {
        if (_ChildrenRects == null) _ChildrenRects = new Dictionary<UIElement, Rect>();
        return _ChildrenRects;
    }
    set => _ChildrenRects = value;
}

var rect = new Rect(x, y, Children[i].DesiredSize.Width, Children[i].DesiredSize.Height);
Children[i].Arrange(rect);
ChildrenRects[Children[i]] = rect;

//从Item获取在Panel中的布局信息
private Rect? GetItemRect(object Item)
{
    var itemContainer = base.ContainerFromItem(Item) as UIElement;
    if (itemContainer != null && _Panel != null)
    {
        if (_Panel.ChildrenRects.ContainsKey(itemContainer))
        {
            return _Panel.ChildrenRects[itemContainer];
        }
    }
    return null;
}

//从容器获取Item和Index
private int GetIndexFromContainer(UIElement Container, out object Item, IList<object> SourceList = null)
{
    Item = ItemFromContainer(Container);
    if (Item != null)
    {
        if (SourceList == null) SourceList = GetSourceList();
        return SourceList.IndexOf(Item);
    }
    return -1;
}

//获取坐标位置的Item和Index
private int GetIndexFromPosition(Point Position, out object Item)
{
    var sourceList = GetSourceList();

    for (int i = 0; i < sourceList.Count; i++)
    {
        var rect = GetItemRect(sourceList[i]);
        if (!rect.HasValue) break;

        if (rect.Value.Contains(Position))
        {
            Item = sourceList[i];
            return i;
        }
    }
    Item = null;
    return -1;
}

//获取源列表
private IList<object> GetSourceList()
{
    if (ItemsSource == null) return Items.ToList();
    else
    {
        var tmp = new List<object>();
        foreach (var item in (IEnumerable)ItemsSource)
        {
            tmp.Add(item);
        }
        return tmp;
    }
}

int StartIndex = -1;    //本次选择开始的位置
int EndIndex = -1;    //本次选择结束的位置
bool? IsFirstItemHadSelected;    //本次选择是选中后续还是取消选中后续
Point? StartPoint;    //选中开始的坐标
UIElement StartContainer;    //选择开始时的容器

private void OnSelectionStarted(Point Position)
{
    var tmpIndex = GetIndexFromPosition(Position, out var item);
    if (tmpIndex == -1)
    {
        return;
    }
    if (StartIndex < 0)
    {
        StartIndex = tmpIndex;
        IsFirstItemHadSelected = SelectedItems.Contains(item);
        StartContainer = ContainerFromItem(item) as UIElement;
    }
}

private void OnSelecting(UIElement Container)
{
    if (IsFirstItemHadSelected.HasValue)
    {
        var sourceList = GetSourceList();
        var tmpIndex = GetIndexFromContainer(Container, out var item, sourceList);
        if (tmpIndex == -1) return;
        if (StartIndex < 0)
        {
            StartIndex = tmpIndex;
            return;
        }
        else
        {
            EndIndex = tmpIndex;
            if (EndIndex >= 0)
            {
                for (int i = Math.Min(StartIndex, EndIndex); i <= Math.Max(StartIndex, EndIndex); i++)
                {
                    if (IsFirstItemHadSelected.Value)
                    {
                        if (SelectedItems.Contains(sourceList[i])) SelectedItems.Remove(sourceList[i]);
                    }
                    else
                    {
                        if (!SelectedItems.Contains(sourceList[i])) SelectedItems.Add(sourceList[i]);
                    }

                }
            }

        }
    }

}

private void OnSelectionComplated()
{
    StartIndex = -1;
    EndIndex = -1;
    IsFirstItemHadSelected = null;
    StartPoint = null;
    StartContainer = null;
}

private void Container_PointerEntered(object sender, PointerRoutedEventArgs e)
{
    if (IsFirstItemHadSelected.HasValue)
    {
        if (sender is UIElement ele && ele != StartContainer)
        {
            if (StartContainer == null)
            {
                StartContainer = ele;
                StartIndex = GetIndexFromContainer(StartContainer, out var item);
            }
            else
            {
                OnSelecting(ele);
            }
        }
    }
}

private void _PointerPressed(object sender, PointerRoutedEventArgs e)
{
    StartPoint = e.GetCurrentPoint(ItemsGrid).Position;
    OnSelectionStarted(StartPoint.Value);
    IsSwipeEnable = true;
}

private void _PointerReleased(object sender, PointerRoutedEventArgs e)
{
    if (IsSwipeEnable.HasValue)
    {
        OnSelectionComplated();
    }
}