/// <summary>
/// 添加或移除一个元素布局
/// </summary>
private void LayoutItem(UIElement item)
{
//开始布局
StackLayoutContext minStack = layoutContext.First(c => c.Lenght == layoutContext.Min(s => s.Lenght));
if (Orientation == Orientation.Vertical)
{
Size availableSize = new Size(minStack.Width, double.PositiveInfinity);
Point coordinate = new Point(minStack.Offset, minStack.Lenght);
item.Measure(availableSize);
SetArrange(item, new Rect(coordinate, item.DesiredSize));
minStack.Lenght += item.DesiredSize.Height + ItemsSpacing;
}
else
{
Size availableSize = new Size(double.PositiveInfinity, minStack.Width);
Point coordinate = new Point(minStack.Lenght, minStack.Offset);
item.Measure(availableSize);
SetArrange(item, new Rect(coordinate, item.DesiredSize));
minStack.Lenght += item.DesiredSize.Width + ItemsSpacing;
}
if (item is IVirtualizingItem)
{
if (ShouldBeVirtualized(item))
{
(item as IVirtualizingItem).Virtualize();
}
else
{
if (minStack.FirstRealizedItemIndex == -1)
{
minStack.FirstRealizedItemIndex = minStack.Elements.Count;
}
minStack.RealizedItemCount++;
(item as IVirtualizingItem).Realize();
}
}
minStack.Elements.Add(item);
//完成一个子项布局,布局请求递减
layoutRequest--;
}
/// <summary>
/// 布局初始化,初始化所有子项的布局
/// </summary>
private void LayoutInitialize(Size availableSize)
{
//清除布局上下文数据
layoutContext.Clear();
double availableWidth = availableSize.Width - Padding.Left - Padding.Right;
double availableHeight = availableSize.Height - Padding.Top - Padding.Bottom;
//计算子项固定边大小
_columnWidth = Math.Min(DesiredColumnWidth, availableWidth);
int numColumns = Math.Max(1, (int)Math.Floor(availableWidth / _columnWidth));
double totalWidth = _columnWidth + ((numColumns - 1) * (_columnWidth + ColumnSpacing));
if (totalWidth > availableWidth)
{
numColumns--;
}
else if (double.IsInfinity(availableWidth))
{
availableWidth = totalWidth;
}
if (HorizontalAlignment == HorizontalAlignment.Stretch)
{
availableWidth = availableWidth - ((numColumns - 1) * ColumnSpacing);
_columnWidth = availableWidth / numColumns;
}
double offset = ((Orientation == Orientation.Vertical ? availableWidth : availableHeight) - (numColumns * ColumnSpacing)) / numColumns;
//为每个栈生成布局上下文数据
for (int i = 0; i < numColumns; i++)
{
layoutContext.Add(new StackLayoutContext()
{
//每个栈的子项的固定偏移,纵向排版就为 X 坐标,横向就为 Y 坐标
Offset = (offset + ColumnSpacing) * i,
Width = offset
});
}
//遍历子项为每个子项进行测量
foreach (var item in this.Children)
{
//寻找长度最短的栈
StackLayoutContext minStack = layoutContext.First(c => c.Lenght == layoutContext.Min(s => s.Lenght));
//根据不同的布局方向进行布局
if (Orientation == Orientation.Vertical)
{
//栈的固定长度,纵向排版为宽,横向为高
availableSize.Width = offset;
//子项的坐标,栈的目前长度与栈的固定偏移
Point coordinate = new Point(minStack.Offset, minStack.Lenght);
//测量子项所需尺寸
item.Measure(availableSize);
//将测量结果保存在附加属性 Arrange 中,以便布局时使用
SetArrange(item, new Rect(coordinate, item.DesiredSize));
//将最短栈加上当前子项的长度与子项间距
minStack.Lenght += item.DesiredSize.Height + ItemsSpacing;
}
else
{
availableSize.Height = offset;
Point coordinate = new Point(minStack.Lenght, minStack.Offset);
item.Measure(availableSize);
SetArrange(item, new Rect(coordinate, item.DesiredSize));
minStack.Lenght += item.DesiredSize.Width + ItemsSpacing;
}
//判断子项是否实现 IVirtualizingItem 接口
if (item is IVirtualizingItem)
{
//判断子项是否应该被虚拟化
if (ShouldBeVirtualized(item))
{
(item as IVirtualizingItem).Virtualize();
}
else
{
if (minStack.FirstRealizedItemIndex == -1)
{
minStack.FirstRealizedItemIndex = minStack.Elements.Count;
}
minStack.RealizedItemCount++;
(item as IVirtualizingItem).Realize();
}
}
//添加子项到最短栈的结尾
minStack.Elements.Add(item);
}
layoutRequest = 0;
}
