c# - Wpf 数据网格 : how to detect the set of visible cells?

Question

我有一个 Wpf DataGrid，用户可以通过单击任何标题进行排序，然后滚动。有些单元格需要显示图像，但我想避免在填充 DataGrid 时加载所有图像。相反，我希望仅在图像进入视野时才加载图像。当单元格进入 View 时如何通知我，以及如何获取其绑定(bind)项？

Answer 1

我最终得到了这个解决方案:监听 DataGrid 的 ScrollViewer.ScrollChanged 事件:

<DataGrid ScrollViewer.ScrollChanged="DataGrid_ScrollChanged">

然后，使用 scrollviewer 属性检测可见行；最后使用 DataGrid 的 ItemContainerGenerator 来获取与感兴趣的每一行关联的项目。

    private static T GetChildOfType<T>(DependencyObject depObj)
        where T : DependencyObject
    {
        if (depObj == null) return null;

        for (int i = 0; i < VisualTreeHelper.GetChildrenCount(depObj); i++)
        {
            var child = VisualTreeHelper.GetChild(depObj, i);

            var result = (child as T) ?? GetChildOfType<T>(child);
            if (result != null) return result;
        }
        return null;
    }

    private void DataGrid_ScrollChanged(object sender, ScrollChangedEventArgs e)
    {
        var scroll = GetChildOfType<ScrollViewer>((DependencyObject)sender);
        int firstRow = (int)scroll.VerticalOffset;
        int lastRow = (int)scroll.VerticalOffset + (int)scroll.ViewportHeight + 1;
        DataGrid datagrid = sender as DataGrid;
        for (int i = firstRow; i < lastRow; i++)
        {
            var row = datagrid.ItemContainerGenerator.ContainerFromIndex(i) as DataGridRow;
            if (row != null)
            {
                var item = row.DataContext;
                ItemViewModel viewModel = item as ItemViewModel;
                if (viewModel != null)
                {
                    viewModel.LoadImages().ContinueWith(t => { });
                }
            }
        }
    }