C# 类型为'的对象；Xamarin.Forms.ViewCell'；无法转换为类型'；Xamarin.Forms.View'；

我在这行代码的HomeViewCell.xamlg.cs中遇到以下异常（类型为“Xamarin.Forms.ViewCell”的对象无法转换为类型为“Xamarin.Forms.View”）： global:：Xamarin.Forms.Xaml.Extensions.LoadFromXaml（this，typeof（HomeViewCell））

基本上，我有

ViewCell
   ContentView
     ContentView.Content
       Grid
         GridRows
         GridColumns
         ViewCell  // Feature ViewCell
           ViewCell.View
             Label (for testing only)
           ViewCell.View
         ViewCell
         ... (8 More ViewCells, same as above)  // FeedItems ViewCell
         ViewCell. // Other ViewCell
           ViewCell.View
             Label (for testing only)
           ViewCell.View
         ViewCell
       Grid
    ContentView.Content
  ContentView
ViewCell

使用Xamarin表单，我试图创建一个ListView项目模板，其中ListView绑定到包含GroupedFeedItem模型列表的ObservableCollection（GroupedFeedItemList）。其中ListView中的每一行都将显示GroupedFeedItem

GroupedFeedItem
{
    FeatureItem {get; set; }
    FeedList1-8 { get; set; }  // 6 items
    OtherFeedList1-2 { get; set; }  // 2 items
}

ObservableCollection<GroupedFeedItem> GroupedFeedItemList

HomeViewCell.xaml

   <?xml version="1.0" encoding="UTF-8"?>
    <ViewCell xmlns="http://xamarin.com/schemas/2014/forms" 
        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
        x:Class="MyApp.CustomCells.HomeViewCell"
        xmlns:local="clr-namespace:MyApp;assembly=MyApp"
        xmlns:commonConverters="clr-namespace:MyApp.Common.Converters;assembly=MyApp.Common">
        <ContentView>
            <ContentView.Content>

                <Grid x:Name="contentGrid" HorizontalOptions="FillAndExpand" Padding="0" VerticalOptions="FillAndExpand" >

                    <Grid.Resources>
                        <ResourceDictionary>
                            <commonConverters:ImageIsVisibleConverter x:Key="ImageIsVisibleConverter"/>
                            <commonConverters:TimeAgoConverter x:Key="TimeAgoConverter"/>
                            <commonConverters:TextColorConverter x:Key="TextColorConverter"/>
                        </ResourceDictionary>
                    </Grid.Resources>

                    <Grid.GestureRecognizers>
                        <TapGestureRecognizer Tapped="HomeViewCell_OnTap" NumberOfTapsRequired="1" />
                    </Grid.GestureRecognizers>

                    <Grid.RowDefinitions>
                        <RowDefinition x:Name="featureGridRow"/>
                        <RowDefinition x:Name="feedItemOneGridRow"/>
                        <RowDefinition x:Name="feedItemTwoGridRow"/>
                        <RowDefinition x:Name="feedItemThreeGridRow"/>
                        <RowDefinition x:Name="feedItemFourGridRow"/>
                        <RowDefinition x:Name="feedItemFiveGridRow"/>
                        <RowDefinition x:Name="feedItemSixGridRow"/>
                        <RowDefinition x:Name="feedItemSevenGridRow"/>
                        <RowDefinition x:Name="feedItemEightGridRow"/>
                        <RowDefinition x:Name="otherGridRow"/>
                    </Grid.RowDefinitions>

                    <Grid.ColumnDefinitions>
                        <ColumnDefinition x:Name="columnOne" Width="*" />
                        <ColumnDefinition x:Name="columnTwo" Width="*" />
                        <ColumnDefinition x:Name="columnThree" Width="*" />
                        <ColumnDefinition x:Name="columnFour" Width="*" />
                        <ColumnDefinition x:Name="columnFive" Width="*" />
                        <ColumnDefinition x:Name="columnSix" Width="*" />
                    </Grid.ColumnDefinitions>

                    <ViewCell x:Name="featureViewCell">
                        <ViewCell.View>
                            <Label Text="FEATURE CELL HERE" />
                        </ViewCell.View>
                    </ViewCell>

                    <ViewCell x:Name="feedItemOneViewCell">
                       <ViewCell.View>
                            <Label Text="FEED CELL ONE HERE" />
                        </ViewCell.View>
                    </ViewCell>

                    <ViewCell x:Name="feedItemTwoViewCell">
                        <ViewCell.View>
                            <Label Text="FEED CELL TWO HERE" />
                        </ViewCell.View>
                    </ViewCell>

                    <ViewCell x:Name="feedItemThreeViewCell">
                        <ViewCell.View>
                            <Label Text="FEED CELL THREE HERE" />
                        </ViewCell.View>
                    </ViewCell>

                    <ViewCell x:Name="feedItemFourViewCell">
                        <ViewCell.View>
                            <Label Text="FEED CELL FOUR HERE" />
                        </ViewCell.View>
                    </ViewCell>

                    <ViewCell x:Name="feedItemFiveViewCell">
                        <ViewCell.View>
                            <Label Text="FEED CELL FIVE HERE" />
                        </ViewCell.View>
                    </ViewCell>

                    <ViewCell x:Name="feedItemSixViewCell">
                        <ViewCell.View>
                            <Label Text="FEED CELL SIX HERE" />
                        </ViewCell.View>
                    </ViewCell>

                    <ViewCell x:Name="feedItemSevenViewCell">
                        <ViewCell.View>
                            <Label Text="FEED CELL SEVEN HERE" />
                        </ViewCell.View>
                    </ViewCell>

                    <ViewCell x:Name="feedItemEightViewCell">
                        <ViewCell.View>
                            <Label Text="FEED CELL EIGHT HERE" />
                        </ViewCell.View>
                    </ViewCell>

                    <ViewCell x:Name="otherViewCell">
                        <ViewCell.View>
                            <Label Text="OTHER FEED CELL HERE" />
                        </ViewCell.View>
                    </ViewCell>

                </Grid>

            </ContentView.Content>

        </ContentView>
    </ViewCell>

HomeListItemTemplateSelector.cs

public class HomeListItemTemplateSelector : DataTemplateSelector
{
    private readonly XXX _xxx;

    private readonly DataTemplate _featureTemplate; 
    private readonly DataTemplate _feed1Template;
    private readonly DataTemplate _feed2Template;
    private readonly DataTemplate _feed3Template;
    private readonly DataTemplate _feed4Template;
    private readonly DataTemplate _feed5Template;
    private readonly DataTemplate _homeViewTemplate;
    private readonly DataTemplate _feed6Template;
    private readonly DataTemplate _feed7Template;
    private readonly DataTemplate _otherTemplate;

    public HomeListItemTemplateSelector(XXX xxx)
    {
        _xxx = xxx;

        this._homeViewTemplate = new DataTemplate(() => new HomeViewCell(_xxx));
        this._featureTemplate = new DataTemplate(() => new FeatureViewCell(_xxx));
        this._feed1Template = new DataTemplate(() => new Feed1ViewCell(_xxx));
        this._feed2Template = new DataTemplate(() => new Feed2ViewCell(_xxx));
        this._feed3Template = new DataTemplate(() => new Feed3ViewCell(_xxx));
        this._feed4Template = new DataTemplate(() => new Feed4ViewCell(_xxx));
        this._feed5Template = new DataTemplate(() => new Feed5ViewCell(_xxx));
        this._feed6Template = new DataTemplate(() => new Feed6ViewCell(_xxx));
        this._feed7Template = new DataTemplate(() => new Feed7ViewCell(_xxx));
        this._otherTemplate = new DataTemplate(() => new OtherViewCell(_xxx));
    }

    DataTemplate SelectViewType(ContentTypeEnum contentType)
    {
        switch (contentType)
        {
            case ContentTypeEnum.Home:
                return this._homeViewTemplate;

            case ContentTypeEnum.Feature:
                return this._featureTemplate;

            case ContentTypeEnum.Feed1:
                return this._feed1Template;

            case ContentTypeEnum.Feed2:
                return this._feed2Template;

            case ContentTypeEnum.Feed3:
                return this._feed3Template;

            case ContentTypeEnum.Feed4:
                return this._feed4Template;

            case ContentTypeEnum.Feed5:
                return this._feed5Template;

            case ContentTypeEnum.Feed6:
                return this._feed6Template;

            case ContentTypeEnum.Feed7:
                return this._feed7Template;

            case ContentTypeEnum.OtherFeed:
                return this._otherTemplate;
        }
        throw new NotImplementedException("Content type not implemented");
    }

    protected override DataTemplate OnSelectTemplate(object item, BindableObject container)
    {
        ...
    }
}

---

你不能筑巢。在ViewCell模板中，您需要使用ContentView，而不是额外的ViewCells您不能像@Jason所说的那样嵌套单元格。并建议删除HomeViewCell.xaml上的标记。

public partial class HomeViewCell : ViewCell
{
    private XXX _xxx = null;

    public HomeViewCell(XXX xxx)
    {
        InitializeComponent();

        _xxx = xxx;

        SetGridRowHeight();
        SetViewCellLocationsInGrid();
    }

    bool isLandscape()
    {
        if (this.View.Height > this.View.Width)  // Portrait OR 0
        {
            return false;
        }
        else  // Landscape
        {
            return true;
        }
    }

    void SetGridRowHeight()
    {
        GridLength featureGridRowHeight = (Device.Idiom == TargetIdiom.Phone)
            ? new GridLength(300)
            : new GridLength(500);

        GridLength feedItemGridRowHeight = (Device.Idiom == TargetIdiom.Phone)
            ? new GridLength(150)
            : new GridLength(300);

        featureGridRow.Height = featureGridRowHeight;

        feedItemOneGridRow.Height = feedItemGridRowHeight;
        feedItemTwoGridRow.Height = feedItemGridRowHeight;
        feedItemThreeGridRow.Height = feedItemGridRowHeight;
        feedItemFourGridRow.Height = feedItemGridRowHeight;
        feedItemFiveGridRow.Height = feedItemGridRowHeight;
        feedItemSixGridRow.Height = feedItemGridRowHeight;
        feedItemSevenGridRow.Height = feedItemGridRowHeight;
        feedItemEightGridRow.Height = feedItemGridRowHeight;

        twitterGridRow.Height = (Device.Idiom == TargetIdiom.Phone)
            ? new GridLength(100)
            : new GridLength(200);
    }

    void SetViewCellLocationsInGrid()
    {
        int featureColumnSpan = (Device.Idiom == TargetIdiom.Phone)
            ? 6
            : isLandscape()  // Tablet
                ? 4
                : 6;

        int feedItemColumnSpan = (Device.Idiom == TargetIdiom.Phone)
            ? 6
            : 3;

        // featureViewCell
        Grid.SetRow(featureViewCell, 0);
        Grid.SetRowSpan(featureViewCell, 0);
        Grid.SetColumn(featureViewCell, 0);
        Grid.SetColumnSpan(featureViewCell, featureColumnSpan);

        // feedItemOneViewCell
        Grid.SetRow(feedItemOneViewCell, 1);
        Grid.SetRowSpan(feedItemOneViewCell, 1);
        Grid.SetColumn(feedItemOneViewCell, 0);
        Grid.SetColumnSpan(feedItemOneViewCell, feedItemColumnSpan);

        // feedItemTwoViewCell
        Grid.SetRow(feedItemTwoViewCell, 2);
        Grid.SetRowSpan(feedItemTwoViewCell, 1);
        Grid.SetColumn(feedItemTwoViewCell, 0);
        Grid.SetColumnSpan(feedItemTwoViewCell, feedItemColumnSpan);

        // feedItemThreeViewCell
        Grid.SetRow(feedItemThreeViewCell, 3);
        Grid.SetRowSpan(feedItemThreeViewCell, 1);
        Grid.SetColumn(feedItemThreeViewCell, 0);
        Grid.SetColumnSpan(feedItemThreeViewCell, feedItemColumnSpan);

        // feedItemFourViewCell
        Grid.SetRow(feedItemFourViewCell, 4);
        Grid.SetRowSpan(feedItemFourViewCell, 1);
        Grid.SetColumn(feedItemFourViewCell, 0);
        Grid.SetColumnSpan(feedItemFourViewCell, feedItemColumnSpan);

        // feedItemFiveViewCell
        Grid.SetRow(feedItemFiveViewCell, 5);
        Grid.SetRowSpan(feedItemFiveViewCell, 1);
        Grid.SetColumn(feedItemFiveViewCell, 0);
        Grid.SetColumnSpan(feedItemFiveViewCell, feedItemColumnSpan);

        // feedItemSixViewCell
        Grid.SetRow(feedItemSixViewCell, 6);
        Grid.SetRowSpan(feedItemSixViewCell, 1);
        Grid.SetColumn(feedItemSixViewCell, 0);
        Grid.SetColumnSpan(feedItemSixViewCell, feedItemColumnSpan);

        // feedItemSevenViewCell
        Grid.SetRow(feedItemSevenViewCell, 7);
        Grid.SetRowSpan(feedItemSevenViewCell, 1);
        Grid.SetColumn(feedItemSevenViewCell, 0);
        Grid.SetColumnSpan(feedItemSevenViewCell, feedItemColumnSpan);

        // feedItemEightViewCell
        Grid.SetRow(feedItemEightViewCell, 8);
        Grid.SetRowSpan(feedItemEightViewCell, 1);
        Grid.SetColumn(feedItemEightViewCell, 0);
        Grid.SetColumnSpan(feedItemEightViewCell, feedItemColumnSpan);

        // otherViewCell
        Grid.SetRow(otherViewCell, 9);
        Grid.SetRowSpan(otherViewCell, 1);
        Grid.SetColumn(otherViewCell, 0);
        Grid.SetColumnSpan(otherViewCell, 6);
    }

    protected override void OnBindingContextChanged()
    {
        base.OnBindingContextChanged();
    }

    public void HomeViewCell_OnTap(object sender, System.EventArgs e)
    {

    }
}

public class HomeListItemTemplateSelector : DataTemplateSelector
{
    private readonly XXX _xxx;

    private readonly DataTemplate _featureTemplate; 
    private readonly DataTemplate _feed1Template;
    private readonly DataTemplate _feed2Template;
    private readonly DataTemplate _feed3Template;
    private readonly DataTemplate _feed4Template;
    private readonly DataTemplate _feed5Template;
    private readonly DataTemplate _homeViewTemplate;
    private readonly DataTemplate _feed6Template;
    private readonly DataTemplate _feed7Template;
    private readonly DataTemplate _otherTemplate;

    public HomeListItemTemplateSelector(XXX xxx)
    {
        _xxx = xxx;

        this._homeViewTemplate = new DataTemplate(() => new HomeViewCell(_xxx));
        this._featureTemplate = new DataTemplate(() => new FeatureViewCell(_xxx));
        this._feed1Template = new DataTemplate(() => new Feed1ViewCell(_xxx));
        this._feed2Template = new DataTemplate(() => new Feed2ViewCell(_xxx));
        this._feed3Template = new DataTemplate(() => new Feed3ViewCell(_xxx));
        this._feed4Template = new DataTemplate(() => new Feed4ViewCell(_xxx));
        this._feed5Template = new DataTemplate(() => new Feed5ViewCell(_xxx));
        this._feed6Template = new DataTemplate(() => new Feed6ViewCell(_xxx));
        this._feed7Template = new DataTemplate(() => new Feed7ViewCell(_xxx));
        this._otherTemplate = new DataTemplate(() => new OtherViewCell(_xxx));
    }

    DataTemplate SelectViewType(ContentTypeEnum contentType)
    {
        switch (contentType)
        {
            case ContentTypeEnum.Home:
                return this._homeViewTemplate;

            case ContentTypeEnum.Feature:
                return this._featureTemplate;

            case ContentTypeEnum.Feed1:
                return this._feed1Template;

            case ContentTypeEnum.Feed2:
                return this._feed2Template;

            case ContentTypeEnum.Feed3:
                return this._feed3Template;

            case ContentTypeEnum.Feed4:
                return this._feed4Template;

            case ContentTypeEnum.Feed5:
                return this._feed5Template;

            case ContentTypeEnum.Feed6:
                return this._feed6Template;

            case ContentTypeEnum.Feed7:
                return this._feed7Template;

            case ContentTypeEnum.OtherFeed:
                return this._otherTemplate;
        }
        throw new NotImplementedException("Content type not implemented");
    }

    protected override DataTemplate OnSelectTemplate(object item, BindableObject container)
    {
        ...
    }
}