c# - NaN 不是有效的宽度值

Question

在 Xamarin.Forms 2.3.4.192-pre2 中，我创建了一个自定义 ViewCell，它使用 Xamarin.Forms.ListView 的 DataTemplate 的网格.

加载ListView时，它会抛出System.ArgumentException:NaN不是有效的宽度值。

我找到了error in the Xamarin.Forms source code ，但我不明白为什么宽度会是 NaN

错误

System.ArgumentException: NaN is not a valid value for width

Xamarin.Forms.Size.Size(double width, double height) Xamarin.Forms.VisualElement.GetSizeRequest(double widthConstraint, double heightConstraint) Xamarin.Forms.VisualElement.Measure(double widthConstraint, double heightConstraint, MeasureFlags flags) Xamarin.Forms.StackLayout.CompressHorizontalLayout(StackLayout.LayoutInformation layout, double widthConstraint, double heightConstraint) Xamarin.Forms.StackLayout.CompressNaiveLayout(StackLayout.LayoutInformation layout, StackOrientation orientation, double widthConstraint, double heightConstraint) Xamarin.Forms.StackLayout.CalculateLayout(StackLayout.LayoutInformation layout, double x, double y, double widthConstraint, double heightConstraint, bool processExpanders) Xamarin.Forms.StackLayout.LayoutChildren(double x, double y, double width, double height) Xamarin.Forms.Layout.UpdateChildrenLayout() Xamarin.Forms.Layout.OnSizeAllocated(double width, double height) Xamarin.Forms.VisualElement.SizeAllocated(double width, double height) Xamarin.Forms.VisualElement.SetSize(double width, double height) Xamarin.Forms.VisualElement.set_Bounds(Rectangle value) Xamarin.Forms.VisualElement.Layout(Rectangle bounds) Xamarin.Forms.Layout.LayoutChildIntoBoundingRegion(VisualElement child, Rectangle region) Xamarin.Forms.Grid.LayoutChildren(double x, double y, double width, double height) Xamarin.Forms.Layout.UpdateChildrenLayout() Xamarin.Forms.Layout.OnSizeAllocated(double width, double height) Xamarin.Forms.VisualElement.SizeAllocated(double width, double height) Xamarin.Forms.VisualElement.SetSize(double width, double height) Xamarin.Forms.VisualElement.set_Bounds(Rectangle value) Xamarin.Forms.VisualElement.Layout(Rectangle bounds) Xamarin.Forms.Layout.LayoutChildIntoBoundingRegion(VisualElement child, Rectangle region) Xamarin.Forms.Platform.iOS.ViewCellRenderer.ViewTableCell.LayoutSubviews() Xamarin.Forms.Platform.iOS.CellTableViewCell.GetNativeCell(UITableView tableView, Cell cell, bool recycleCells, string templateId) Xamarin.Forms.Platform.iOS.ListViewRenderer.ListViewDataSource.GetCell(UITableView tableView, NSIndexPath indexPath) UIKit.UIApplication.UIApplicationMain(int, string[], intptr, intptr)(wrapper managed-to-native) UIKit.UIApplication.Main(string[] args, IntPtr principal, IntPtr delegate)UIApplication.cs:79 UIKit.UIApplication.Main(string[] args, string principalClassName, string delegateClassName)UIApplication.cs:63 MondayPundayApp.iOS.Application.Main(string[] args)Main.cs:17

代码

我在 GitHub 上的这个存储库中整理了一个复制品: https://github.com/brminnick/Xamarin.Forms-NaN-is-not-a-valid-value-for-width-reproduction

ListView

var listView = new ListView(ListViewCachingStrategy.RecycleElement)
{
    BackgroundColor = Color.White,
    RowHeight = 200,
    ItemTemplate = new DataTemplate(typeof(PuzzleCellCardView)),
    SeparatorColor = Color.Transparent
};

ViewCell

public class PuzzleCellCardView : ViewCell
{
    Image _puzzleImage;
    Label _punNumberValueLabel;
    Image _questionMarkImage;
    Image _checkImage;

    public PuzzleCellCardView()
    {
        var puzzleImage = new Image
        {
            HeightRequest = 150,
            BackgroundColor = Color.White
        };

        var punNumberTextLabel = new Label
        {
            Text = " Pun Number",
            Style = StyleConstants.LabelStyle
        };

        _punNumberValueLabel = new Label
        {
            Style = StyleConstants.LabelStyle
        };

        var puzzleNumberStackLayout = new StackLayout
        {
            Children = {
                punNumberTextLabel,
                _punNumberValueLabel
            },
            Orientation = StackOrientation.Horizontal,
            BackgroundColor = Color.White
        };

        _questionMarkImage = new Image
        {
            Source = App.ImageConstants.QuestionMark,
            MinimumHeightRequest = 100,
            BackgroundColor = Color.White
        };

        _checkImage = new Image
        {
            Source = App.ImageConstants.Check,
            MinimumHeightRequest = 100,
            BackgroundColor = Color.White
        };

        var whitePuzzleNumberBackgroundBoxView = new BoxView
        {
            BackgroundColor = Color.White
        };

        var cellGridLayout = new Grid
        {
            BackgroundColor = Color.Black,
            Padding = new Thickness(2),
            RowSpacing = 2,
            ColumnSpacing = 1,
            VerticalOptions = LayoutOptions.Fill,

            RowDefinitions = {
                new RowDefinition{ Height = new GridLength (20, GridUnitType.Absolute) },
                new RowDefinition{ Height = new GridLength (150, GridUnitType.Absolute) }
            },
            ColumnDefinitions = {
                new ColumnDefinition{ Width = new GridLength (1, GridUnitType.Star) },
                new ColumnDefinition{ Width = new GridLength (1, GridUnitType.Star) }
            }
        };
        cellGridLayout.Children.Add(whitePuzzleNumberBackgroundBoxView, 0, 0);
        Grid.SetColumnSpan(whitePuzzleNumberBackgroundBoxView, 2);

        cellGridLayout.Children.Add(puzzleNumberStackLayout, 0, 0);
        Grid.SetColumnSpan(puzzleNumberStackLayout, 2);

        cellGridLayout.Children.Add(_puzzleImage, 0, 1);

        cellGridLayout.Children.Add(_checkImage, 1, 1);
        cellGridLayout.Children.Add(_questionMarkImage, 1, 1);

        if (Device.OS == TargetPlatform.Android)
            _puzzleImage.InputTransparent = true;

        View = cellGridLayout;
    }
}

Answer 1

这似乎是 Xamarin.Forms v2.3.4.192-pre2 的回归。

使用 Xamarin.Forms v2.3.3.180 时不会引发异常。

我通过 Bugzilla 向 Xamarin.Forms 团队提交了错误:https://bugzilla.xamarin.com/show_bug.cgi?id=52533

更新:此错误已在 Xamarin.Forms 2.3.4.214-pre5 中修复