我可以制作一个考虑到 ListView 单元格大小变化的事件处理程序。这是它:
<ListView ItemsSource="{Binding Items}"
VerticalOptions="Start"
HasUnevenRows="true"
CachingStrategy="RecycleElement"
SelectionMode="None"
SizeChanged="ListView_OnSizeChanged">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell >
<Frame Padding="10,0" SizeChanged="VisualElement_OnSizeChanged">
Frame 可以通过 Grid、StackLayout 等进行更改。xaml.cs:
static readonly Dictionary<ListView, Dictionary<VisualElement, int>> _listViewHeightDictionary = new Dictionary<ListView, Dictionary<VisualElement, int>>();
private void VisualElement_OnSizeChanged(object sender, EventArgs e)
{
var frame = (VisualElement) sender;
var listView = (ListView)frame.Parent.Parent;
var height = (int) frame.Measure(1000, 1000, MeasureFlags.IncludeMargins).Minimum.Height;
if (!_listViewHeightDictionary.ContainsKey(listView))
{
_listViewHeightDictionary[listView] = new Dictionary<VisualElement, int>();
}
if (!_listViewHeightDictionary[listView].TryGetValue(frame, out var oldHeight) || oldHeight != height)
{
_listViewHeightDictionary[listView][frame] = height;
var fullHeight = _listViewHeightDictionary[listView].Values.Sum();
if ((int) listView.HeightRequest != fullHeight
&& listView.ItemsSource.Cast<object>().Count() == _listViewHeightDictionary[listView].Count
)
{
listView.HeightRequest = fullHeight;
listView.Layout(new Rectangle(listView.X, listView.Y, listView.Width, fullHeight));
}
}
}
private void ListView_OnSizeChanged(object sender, EventArgs e)
{
var listView = (ListView)sender;
if (listView.ItemsSource == null || listView.ItemsSource.Cast<object>().Count() == 0)
{
listView.HeightRequest = 0;
}
}
当 Frame 显示时(ListView.ItemTemplate 正在应用),frame 的大小发生变化。我们通过 Measure() 方法获取它的实际高度并将其放入 Dictionary 中,它知道当前 ListView 并保存 Frame 的高度。当显示最后一帧时,我们将所有高度相加。如果没有项目,ListView_OnSizeChanged() 将 listView.HeightRequest 设置为 0。