Question

在ListView中，我想绑定一个网格columnSpan，然后在ItemSource对象中设置它。这是我试图实现这一点的方式，但我得到：，对象引用没有设置为对象的实例“。我想知道什么是正确的方法，如果需要使用任何ValueConverter来设置span属性。 “标题”文本属性目前并不重要。

ViewCell：

class CustomPerformanceCell : ViewCell
{
    public CustomPerformanceCell()
    {

        var titleLabel = new Label();
        titleLabel.SetBinding(Label.TextProperty , "Title");

        var resultGrid = new Grid
        {
            HorizontalOptions = LayoutOptions.FillAndExpand
        };
        resultGrid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) });
        resultGrid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) });
        resultGrid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) });

        resultGrid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });
        resultGrid.BackgroundColor = Color.DarkGray;

        var ColorBox = new BoxView();
        ColorBox.SetBinding(VisualElement.BackgroundColorProperty, "BackgroundColor", BindingMode.Default, new BackgroundConverter(), null);
        resultGrid.Children.Add(ColorBox ,0,0);
        ColorBox.SetBinding(Grid.ColumnSpanProperty, "Performance");

    }
}

PerformanceCell：

public class PerformanceCellItem
{
    public string Title { get; set; }
    public int Performance { get; set; }
    public string BackgroundColor { get; set; }

    public PerformanceCellItem(string title, int performance ,string backgroundColor)
    {
        Title = title;
        Performance = performance;
        BackgroundColor = backgroundColor;
    }
}

创建它的功能：

 public void PreparePerformanceStack()
    {
        PerformanceList = new ListView
        {
            ItemTemplate = new DataTemplate(typeof(CustomPerformanceCell))
        };
        ObservableCollection<PerformanceCellItem> cellItems = new ObservableCollection<PerformanceCellItem>
        {
            new PerformanceCellItem("test 1", 2,"#00AA00"),
            new PerformanceCellItem("test 2",  2,"#00AA00"),
            new PerformanceCellItem("test 3",  2,"#00AA00")
        };
        PerformanceList.ItemsSource = cellItems;
    }

Answer 1

ColumnSpan除非有父网格，否则无法设置为Grid;如果您想将其设置为BoxView - 请使用colorBox.SetBinding(Grid.ColumnSpanProperty, "Performance")。

另外，请确保Performance的值为＆gt; = 1（否则coerce condition将引发异常）。只要源类型为int或parse-able string，您就不需要值转换器。

编辑1 - 根据问题编辑

您需要在自定义视图单元格中指定View属性

this.View = resultGrid;

在您的构造函数CustomPerformanceCell()

中

在ListView中绑定网格ColumnSpan

1 个答案: